### Produced by The COMET® Program

### Introduction

### Introduction » Challenges of Enroute Icing

Ask pilots which weather condition is most challenging for flying, and many will say icing. Ice accumulation increases aircraft weight and degrades its aerodynamics. Icing impacts depend on aircraft size, wing orientation, and the availability of onboard deicing equipment.

Over the years, aircraft icing has resulted in numerous accidents, some fatal. Often pilots were unaware that icing was imminent, as were the aviation forecasters providing guidance to the air traffic controllers (ATCs). Insufficient awareness was cited as an ongoing problem by the U.S. National Transportation Safety Board (NTSB) in a 2014 report on improving general aviation safety.

### Introduction » About the Lesson

This lesson presents a process for forecasting enroute aviation icing in the context of a case over the CONUS. It focuses on the icing forecast procedure up to the point of issuing products. This involves gaining situational awareness of areas with icing potential, making first forecasts of their locations and flight levels, and comparing them to NWP forecasts, adjusting as needed.

After completing the lesson, users should be able to:

- Identify data products that are useful for identifying and forecasting icing
- Describe associated temperature and moisture profiles that can lead to organized types of icing
- Use observational data and NWP analyses to determine if icing is present
- Develop an icing “first forecast,” identifying expected areas, flight levels, and severity of icing based on initial conditions
- Use the Numerical Weather Prediction (NWP) forecast to modify the first forecast as appropriate

Learners should be familiar with the following before taking this lesson:

- Aircraft icing, including conditions conducive to its formation, such as air temperature, moisture, cloud microphysics, and the formation of supercooled cloud droplets
- Pilot reporting systems (PIREPs) and icing advisories issued as locally required to warn pilots of hazardous flight conditions
- Model products used in aviation forecasting

### Case Study: Overview

In this case study, you’ll examine a weather situation in the U.S. Midwest, concentrating on the service area covered by the Chicago CWSU on 26 to 27 February 2011. The Chicago CWSU area includes southern Wisconsin, southwestern Michigan, northern Indiana, Illinois, and eastern Iowa, as shown below. To see how the Chicago CWSU fits into a larger CONUS context, access the map on an Aviation Weather Center webpage.

In forecasting the risk for icing, we will use the following procedure.

- Diagnose the locations and future evolution of icing: Use observational data and NWP analyses to determine areas and levels of icing across your forecast area, and make a “first forecast” of icing, including severity.
- Adjust forecast of future icing locations, using NWP icing forecast tools to adjust the "first forecast" as needed.

Recall that icing occurs in the presence of supercooled liquid water - in clouds and/or precipitation in regions of sub-freezing temperatures often associated with upward motion near low pressure systems. These layers appear on atmospheric soundings as moist layers with temperatures in the 0°C to -22°C range. While the -22°C is often used as the lower temperature limit for supercooled cloud water, it can be observed at lower temperatures, especially in mountain wave and convective clouds.

NOTE: In this lesson, we will use "flight level" or "FL" for all elevations. In some jurisdictions, including the United States, the standard notation for levels below FL180 is 000'-179' or zero feet to 17900 feet.

### Step 1: Diagnosing Locations of Icing

### Step 1: Diagnosing Locations of Icing » Introduction

Without observational data and NWP analyses, aviation forecasters would be flying blind! NWP analyses fill in gaps between observations, which are often hundreds of miles apart. Observations, in turn, are used to validate NWP analyses and provide confidence in the NWP guidance used to produce the final icing forecast.

In this first step, you will use observational data and NWP analyses to determine areas and levels of icing across your forecast area. Then you’ll make a “first forecast” of icing, including severity. This first forecast is a short-term forecast based on current conditions.

On the next pages, you’ll explore the data, looking for any icing threats. Then you will consolidate your findings and make the first forecast.

### Step 1: Diagnosing Locations of Icing » Surface Chart

Over the central U.S., there is a large high pressure system with cold air near the surface. To its south and west is a stationary front. Light, spotty snow and freezing precipitation are present between the stationary front and the high pressure system.

### Step 1: Diagnosing Locations of Icing » PIREPs and AIREPs

### Step 1: Diagnosing Locations of Icing » PIREPs and AIREPs » Description

Pilot Reports (PIREPs) and Aircraft or Air Reports (AIREPs) are arguably the most important indicators of current conditions. Forecasters use them with other observations to verify NWP analyses.

There are some limitations to be aware of in regard to these data. SInce aircraft tend to avoid areas with icing, there may not be enough reports where they are most needed along flight routes. Note, though, that icing cannot be avoided by commercial aircraft using high volume airports such as Chicago O’Hare (ORD) Thus, their icing reports can be used as a proxy for similar conditions in nearby smaller volume (General Aviation) airports.

Another common problem is that there are few to no PIREPS during the late night and early morning hours when few flights occur. As a result, the icing picture can change when the first PIREPs of the day come in.

PIREPs and AIREPs contain the following:

- Location of PIREP (relative to airports or other identifiers)
- Flight level of PIREP (in hundreds of feet above MSL, for example, FL180 is 18000 feet)
- Ambient temperature in degrees C at the PIREP location
- Type of aircraft
- Pilot-observed icing intensity (NIL, Trace, Light, Moderate, Heavy, or Severe) where heavy and severe icing have the same serious impacts on commercial aircraft

To encourage icing reports, CWSU service area forecasters prompt Air Traffic Controllers (ATC or TRAFCON) to request them from pilots where and when light or greater icing exists or is forecast. When the reports are received or come in unsolicited, the Air Route Traffic Control Center (ARTCC) enters them into the Aeronautical Information System Replacement (AIS-R). The icing reports are used by flight data personnel and the CWSU, and are available from the AIS-R, Flight Service Specialists, and Aviation Weather Center (AWC).

PIREPs and AIREPs are quality controlled before a CWSU issues a Center Weather Advisory (CWA), or a Meteorological Watch Office (MWO) issues an AIRMET or SIGMET. This is done by checking consistency with other observations and analyses. For example, moderate or severe reports in close proximity to similar reports are given more weight than those near nil, trace, or light icing reports. AIREPs and PIREPs from areas determined to be without clouds or precipitation are totally discounted.

Consideration is also given to the type of reporting aircraft and the length of its flight path through potential icing regions. Smaller aircraft often report more severe icing than commercial aircraft because they accumulate ice more readily and do not have icing equipment. Longer flight paths and extended holding periods in icing conditions result in more ice accumulation on all types of aircraft.

### Step 1: Diagnosing Locations of Icing » PIREPs and AIREPs » Data

These PIREPs go from 1000 through 1300 UTC 26 February 2011, with the red lines marking the boundaries of the service area. Green represents light icing, and gold indicates moderate icing. The number adjacent to the report gives the observation flight level in hundreds of feet.

#### Question

Based on the information plotted, what conclusions can you draw about the validity of this icing data in and upstream of the Chicago CWSU service area?

a) The PIREPs are valid because they are similar in intensity to each other
b) The PIREPs are suspect because they are similar in intensity but dissimilar in flight level
c) The PIREPs are valid because they are at similar flight levels
d) The PIREPs are suspect because they are similar in flight level but dissimilar in intensity

The correct answers are a, c.

All PIREPs for icing near the service area indicate light to mostly moderate icing between flight levels 016 and 075.

Please make a selection.

### Step 1: Diagnosing Locations of Icing » Skew-T/Log-P

### Step 1: Diagnosing Locations of Icing » Skew-T/Log-P » Description

Skew-T/Log-P (Skew-T) diagrams provide vertical profiles of temperature and dewpoint from radiosonde launch sites usually every 12 hours, or from NWP model analyses and forecasts. They are used to find saturated or near-saturated layers with temperatures from 0° to about -22°C. The following general rules apply:

- Thicker, moist sub-freezing layers have higher moderate or greater icing risk. If a Skew-T shows a zero dewpoint depression, expect at least moderate icing.
- If the top of a moist layer is colder than -22°C, ice crystals or snowflakes may reduce the amount of supercooled water, reducing the icing risk.
  - Abundant moisture and upward motion located within the snowflake growth zone (Dendritic Zone, between temps -12°C to -18°C) can actually eliminate the amount of supercooled liquid below and thus reduce the potential for aircraft icing. This process is called scrubbing or the seeder/feeder process. Such is the case for some heavy snow storms.
  - Rarely, a separate moist layer above one producing snow may result in icing above the dendritic growth zone.
- Trace or light icing is still possible at temperatures as low as -40°C according to most jet aircraft manuals, particularly in convective clouds.
- Look for multiple layers with icing potential, especially in advance of warm fronts.
- Steep (equal to or greater than moist adiabatic) lapse rates in moist layers can increase icing severity. This results from convective motion embedded in stratiform clouds, resulting in the formation of supercooled large drops. If, however, convective motion becomes vigorous, chances increase for ice crystal formation and the subsequent “scrubbing” of supercooled water from clouds.
- Use Skew-Ts to supplement satellite data in areas of cirrostratus or altostratus. A smaller temperature-dew point spread indicates a greater threat for light to moderate icing.

The flowchart below, taken from the DoD Defense Technical Information Center Technical Note “Meteorological Techniques (2006),” is for use with observed or model soundings. It shows the expected icing type and severity for different temperature and dew point spread thresholds. The two predominant icing situations associated with synoptic scale low pressure systems are enclosed in the red dash. The flowchart for non-frontal or orographic situations, above the red dash box, can be used for situations that do not neatly fit such synoptic-scale situations. Note that moderate to severe clear or mixed icing is generally associated with freezing rain and freezing drizzle (usually found in advance of surface warm fronts), and with stratocumulus and cumulus in cold advection or near deep low pressure areas.

Mouse over the image below to zoom in

### Step 1: Diagnosing Locations of Icing » Skew-T/Log-P » Advantages and Limitations

Skew-T/Log-P diagrams plotting data from radiosondes have the following advantages. They are highly accurate and let you see multiple layers with a high risk for icing. In addition, they can be used to determine if moist layers colder than about -22°C are present, which will produce ice crystals that remove supercooled water. Finally, radiosonde data can be used with satellite and surface data to better specify icing levels.

But data from radiosondes have limitations. The data are sparse and usually taken only every 12 hours. In addition, they only represent a small area around the launch site. In fact, they may not be representative at all if the balloon rises through a local phenomenon, such as a convective cell.

### Step 1: Diagnosing Locations of Icing » Skew-T/Log-P » Data

#### Question

Here’s the Skew-T sounding for Davenport, IA for 12 UTC 26 February 2011. Review it, looking for layers that may contain supercooled water and features that may indicate enhance chances of severe icing. Then use the drawing tools to outline the areas that are at risk for icing. (Click if you'd like to review the Icing Flowchart.)

Use the black pen to circle any layers that may contain supercooled water. Use the red pen to circle any features that may indicate enhanced chances of moderate to severe icing.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The entire layer from 720 hPa to the surface has temperatures from about -13°C to -8°C, and dew point depressions from 0° to 2°C. This layer, circled in black, has conditions that are favorable for icing throughout its 280 hPa depth. Within this deep layer is a conditionally unstable layer between about 730 and 780 hPa circled in red (between FL070 to FL090), in which icing could be further enhanced by convective motion.

Also note the west to west-southwest winds from 800 to 350 hPa in the sounding (FL065 to FL260). These conditions are being advected eastward from Iowa into the service area.

### Step 1: Diagnosing Locations of Icing » Satellite Data

### Step 1: Diagnosing Locations of Icing » Satellite Data » Overview

The satellite channels and products that are useful for determining icing potential include visible (VIS), shortwave IR (SW IR), longwave IR (LW IR), the Cloud Phase and Icing Potential RGB, and water vapor (WV).

Animated imagery from one or more of them lets you see the following:

- The evolution of the atmospheric flow up to the present, allowing the forecaster to make a “first forecast” projection into the future
- The past movement, current location, and possible future movement of moisture, clouds, and potential areas of icing
- The phase of cloud water (supercooled liquid, ice, or above freezing) at the cloud top

#### Question

Although each type of satellite imagery provides unique information about icing, they all share a common limitation. They cannot be used to determine:

a) The existence of supercooled water
b) Cloud top temperature
c) Nighttime cloudiness
d) Multiple cloud layers

The correct answer is d.

Visible and IR satellite data let us see the radiating or reflecting cloud top surface; cloud layers below are obscured. This means that forecasters must use additional tools to assess which flight levels have an icing risk within an area of moisture and clouds.

Option A is incorrect. Individual and multiple IR satellite channels can be used to find potential supercooled water. Option B is incorrect because the cloud top temperature can be determined from the amount of radiation emitted from the cloud top to the satellite. Finally, option C is incorrect because SW IR and LW IR satellite data can be used to find clouds at night.

Please make a selection.

On the next set of pages, we’ll discuss the characteristics that determine how each type of imagery is used in icing diagnosis, and the guidance that imagery can provide. Then we’ll look at the animations for the case. Note that we’ll only show imagery that’s practical for interpreting icing locations.

As you view the animations, look for areas of icing risk, how they are moving, and how they are changing in area coverage. Then on one culminating page, you’ll identify where icing is possible in the service area based on all of the imagery that you have seen.

An important caveat: Satellite imagery only tells part of the story. Forecast soundings, time height diagrams, and other analyses and forecast guidance are needed to refine icing flight levels and severity.

### Step 1: Diagnosing Locations of Icing » Satellite Data » Visible

Visible imagery shows daytime cloud coverage. It can help with icing forecasts by showing:

- Cloud brightness, which increases with cloud opacity, water content, and RH
- Clear to cloudy and cloudy to clear transitions near the front and back edges of icing areas
- Potential convection that looks like “lumpy” cloud areas

When using visible imagery with temperature data from Skew-T diagrams and other sources, we can see where there may be supercooled water. If you can see through a cloud layer to the surface, the icing threat is likely to be minimal.

An obvious limitation to using conventional visible imagery is that it’s only available during daytime. It’s also hard to distinguish visible cloud from snow, although other satellite channels or products can help with this.

Here’s the VIS image from 13:03 UTC 26 February 2011. The sun is just rising in the Chicago CWSU service area, but we can still see suggestions of visible cloud.

### Step 1: Diagnosing Locations of Icing » Satellite Data » SW IR

The shortwave IR channel lets you identify areas of day- and nighttime cloudiness along with cloud water phase during daylight. The reflected amount shows whether the cloud water is in solid or liquid form. Supercooled water clouds are brighter in daytime SW IR images, so brighter areas represent higher icing risk.

While no solar radiation is reflected at night, we can still determine if continuous, thick cirrus layers are present. If urban lights are obscured by a continuous cirrus layer, light to moderate rime icing is possible. A broken cirrus layer with visible urban lights suggests that only trace to light rime icing should be expected.

Radiosonde or model soundings provide additional information. For SW IR, if soundings show small (< 2°C) temperature-dew point spreads at cirrus level, there is a greater light-to-moderate icing threat. Typically, this is rime ice.

Here’s the SW IR animation from approximately 00 to 1302 UTC 26 Feb. Given the time of day, the sunrise terminator sweeping in from the east makes it difficult to use the imagery to diagnose potential icing in the Chicago CWSU service area. Therefore, we will not use it in this case. However, you can use it to check on the location and movement of icing areas later in the day.

### Step 1: Diagnosing Locations of Icing » Satellite Data » LW IR

Longwave infrared imagery gives cloud top temperature, which can be used to infer cloud water phase. Cloud top temperatures between 0° and about -22°C indicate that the cloud likely contains supercooled water. For cloud tops colder than about -22°C, ice crystals at cloud top will reduce the amount of supercooled water, reducing the risk of icing. There is one caveat. Vigorous upward motion often results in abundant snowflakes and minimal icing risk with temperatures somewhat warmer than -22°C.

Here’s the LW IR animation from approximately 00 to 1302 UTC 26 Feb. View it, making a mental note of areas that may contain supercooled water.

### Step 1: Diagnosing Locations of Icing » Satellite Data » Cloud Phase and Icing Potential RGB

The Cloud Phase and Icing Potential RGB product is made from visible and shortwave and longwave IR channels, and helps locate fog and low clouds. You can infer the presence of supercooled cloud liquid from the vertical temperature structure in the low cloud area.

When the RGB is enhanced with color, you can see where low cloud tops are at supercooled temperatures. In the product:

- Land and water are darker gray
- Water clouds above freezing are white
- Water clouds between -22° and 0°C are light to dark blue
- Ice clouds are dark to light blue-green

Generally, lower, warmer (but still subfreezing) clouds are in liquid form when higher clouds are not present.

The product is useful for distinguishing high-altitude ice clouds from lower-altitude water clouds. However, it has some limitations. Because it uses reflected SW IR solar radiation, it is less useful at night unless supercooled water areas are highlighted using cloud top temperature (as they are in this case). In wintertime polar latitudes where darkness predominates, aviation forecasters can use the 24-hour Microphysics RGB product and other polar-orbiting imagery. For more on the 24-hour Microphysics RGB product, visit the Short-term Prediction Research and Transition Center (SPoRT) website.

The example below is from the animation for the case. As you can see, the area outlined in red has ice clouds; the area in yellow has supercooled cloud water; the area in white has above-freezing cloud water; and the area in gray has ice clouds near the ice/supercooled water threshold.

View the Cloud Phase and Icing Potential RGB animation, which goes from approximately 00 to 1302 UTC 26 Feb. Make a mental note of areas where supercooled cloud, which is conducive to icing, may exist.

### Step 1: Diagnosing Locations of Icing » Satellite Data » Water Vapor

Water vapor imagery lets you determine the water vapor content in an atmospheric column, particularly in the mid to upper troposphere. You can see atmospheric flow through the movement of water vapor features and therefore identify active weather and moist regions with icing potential.

The various colors depict different characteristics:

- Drier areas have orange to red shading
- Moister areas have dark gray to white shading
- Colder, moist areas have purple and blue shading, and may contain icing
- Sharp color gradients from grey/white/purple/blue (moist or moistening, neutral to upward motion) to orange and red (dry or drying, sinking motion) show the location of the jet stream

Here’s the water vapor animation from approximately 00 to 1302 UTC 26 Feb. View it, making a mental note of areas that might be conducive to icing, and moving features in the atmospheric flow that may generate clouds and precipitation.

### Step 1: Diagnosing Locations of Icing » Satellite Data » Culminating Satellite Question

The PIREPS showed areas where light and moderate icing were reported. Satellite imagery can be used to fill in the spaces between reports and give a better representation of the areal extent of icing. Now, we’ll combine the satellite data to determine the areas with the biggest potential for icing.

#### Question

Use the drawing pens to outline the areas from each satellite product that are at risk for icing in the area from Kansas, Missouri, and Kentucky northward to the Canadian border.

Use the black pen to outline areas at risk from icing from the WV product; the red pen for areas with icing risk from the LW IR product; and the blue pen for areas with icing risk from the RGB product.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The map shows the areas with icing risk, color-coded for each satellite product.

The LW IR imagery indicates an area in the southern half of the Chicago CWSU service area with cloud tops in the 0° to -22°C range (in the oval). This region is favorable for supercooled water and icing.

The Cloud Phase and Icing Potential RGB shows a large area of supercooled water clouds in shades of blue from central and southern Illinois south and west to the Texas panhandle, then northward through the western Great Plains. The blue shading represents supercooled cloud tops at 0° to -20°C. The eastern portion of this region is largely consistent with other satellite guidance.

The WV imagery shows gray and enhanced purple to blue shading, indicating a moist environment with some colder cloud tops in the service area. If the colder clouds move over the lower supercooled layers, ice crystals could reduce the supercooled water in the layers below.

### Step 1: Diagnosing Locations of Icing » Satellite Data » Final Icing Diagnosis

This map highlights the region where at least one satellite channel indicates icing risk. The risk covers the entire service area, and well to the west and southwest of there.

Besides areas of icing risk, the infrared and especially water vapor animations show a long fetch of west to southwesterly winds from Baja California to the mid-Atlantic coast indicating the movement of the regions of supercooled water.

### Step 1: Diagnosing Locations of Icing » NEXRAD Radar

### Step 1: Diagnosing Locations of Icing » NEXRAD Radar » Description

Radar shows the location and intensity of precipitation. Where precipitation echoes exist, there is enough condensed cloud water to produce precipitation. Below-freezing air below the melting layer signals a risk for moderate or greater clear or mixed icing if the precipitation has not had a chance to fully refreeze.

Usually, further diagnosis is needed to determine the icing risk. However, radar can be used to find the 0°C isotherm if there is a melting layer aloft where snow transitions to rain. The melting layer shows up as a “bright band” of high-reflectivity melting snow marking the 0°C isotherm. Below-freezing air close to the surface signals a risk for moderate or greater clear or mixed icing. This sample radar from another case has bright banding.

There are many advantages to using radar. It provides clear depictions of precipitation areas and is useful in corroborating freezing precipitation observations (METARs). In addition, the bright banding can be used to locate the precipitation melting level.

But radar has limitations. It lacks information on temperature structure beyond bright banding and cannot locate supercooled moist layers without bright banding. An entire supercooled layer can be “hidden” unless you use other sources for vertical temperature and moisture information, such as a Skew-T.

### Step 1: Diagnosing Locations of Icing » NEXRAD Radar » Data

Here’s the animated regional radar for the mid-Mississippi Valley and lower Midwest from 0900 UTC to 1300 UTC 26 February 2011. Examine the data, then answer the question.

#### Question

Which statements about the radar animation are true?

a) Bright banding is evident over areas west of KORD at 13 UTC
b) Precipitation is decreasing over areas west of KORD at 13 UTC
c) Precipitation is increasing over areas west of KORD at 13 UTC
d) We need more data to determine the locations of potential icing at 13 UTC

The correct answers are c, d.

Option A is incorrect since there’s no bright banding anywhere in the regional radar at 13 UTC. Option B is incorrect and option C correct because radar shows increasing precipitation coverage from 12 to 13 UTC. Option D is also correct because we cannot get information on the vertical temperature structure from the radar data.

Here is the answer in graphical form. The area enclosed in white shows the location of precipitation, and thus areas of potential icing where temperatures are below 0°C.

Please make a selection.

### Step 1: Diagnosing Locations of Icing » METAR Surface Observations

### Step 1: Diagnosing Locations of Icing » METAR Surface Observations » Description

METARs are coded surface observations. They include:

- Cloud cover
- Ceiling height
- Surface temperature, dewpoint, and wind
- Mean sea level pressure and pressure tendency
- Precipitation and precipitation type
- Visibility and visibility obstructions, such as fog, mist, and rain

METARs can be used to quality control PIREPs and estimate the flight levels of clouds. With no precipitation, in-cloud icing may take place from the cloud base upward, given favorable conditions. Where METARs report freezing precipitation, there will be icing from the cloud base to the surface.

Data from METAR plots can also be plotted on a surface chart. An icing risk exists where surface charts and surface weather depictions indicate the following.

Freezing precipitation |
Light rain | Symbols: ∙ for very light rain or – –RA in METAR; or ∙∙ for light rain or –RA in METARs
Light snow | Symbols: * for very light snow or – –SN in METAR; or ** for light snow or –SN in METARs). Note that if moderate to heavy snow (SN to +SN) is reported in a METAR, supercooled water aloft will be removed and icing minimized.

What are the advantages of using METARs and their depictions in surface charts? They are compact descriptions of aviation-relevant ground conditions, and are useful for identifying icing conditions at ground locations. However, when they are reported from automated stations, freezing drizzle or very light snow may not be detected, with mist or haze reported instead.

### Step 1: Diagnosing Locations of Icing » METAR Surface Observations » Data

Here is the METAR for the Chicago O’Hare International Airport (KORD) at 13 UTC 26 February 2011. That’s the same time as the surface map we saw earlier.

METAR KORD 261251Z 05007KT 2.50SM -SN FEW009 OVC014 M03/M04 A2995 RMK AO2 SLP141 P0001 T10331039

#### Question

Here’s a portion of the surface weather depiction used specifically for aviation and issued every three hours, valid at 12 UTC 26 February 2011. Included are the ceiling in hundreds of feet, the visibility in statute miles, cloud coverage, and weather type, all obtained from METAR observations. Where does it indicate an icing risk?

Circle areas of freezing precipitation in red, and areas of very light to light snow in orange.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The light to very light snow locations (✱ and ✱✱) are enclosed in orange. The two stations with freezing precipitation (~) are enclosed by the red contour. Much of the area over and west of the service area has surface conditions that indicate potential icing, especially from Kansas City to St. Louis, MO where the freezing drizzle indicates likely moderate icing.

### Step 1: Diagnosing Locations of Icing » NWP Analyses

### Step 1: Diagnosing Locations of Icing » NWP Analyses » Vertical X-C and Plan View Maps - Description

The most commonly used tools for NWP analyses of icing risk are vertical cross-sections and plan view maps.

Vertical cross sections (X-Cs) show a detailed “slice” of the model atmosphere, plotting temperature T, relative humidity RH, and negative pressure vertical velocity –VVEL. Negative of pressure vertical velocity is used so that upward vertical motion has a positive value. The cross sections help forecasters locate layers of potential icing in or near to that model slice.

P lan view maps are used to find horizontal areas where layer mean temperature T, relative humidity RH, and –VVEL meet icing criteria. The layers often used include:

- 925-850 hPa (about FL20 through FL45)
- 850-700 hPa (about FL45 through FL110)
- 700-500 hPa (about FL110 through FL180)

Be aware that icing can occur above and below these levels. You can use the vertical cross-section to determine the best mean layer map to use.

Icing is likely where the NWP forecast variables all meet the following criteria:

- T (see -VVEL for exceptions to the -22°C lower bound value)
  - 0°C to -22°C in supercooled saturated/near-saturated layer
  - T < ‒22°C within any moist layer(s) usually means trace to mainly light icing; ice crystals remove or grow at the expense of supercooled water
- RH:
  - RH > 80% for icing; > 90% icing near-certainty
- Minus (−) VVEL (positive means upward motion)
  - −VVEL > 0: rising motion, enhanced risk of icing
  - −VVEL < 0: sinking motion, reduced risk of icing
  - Adjust -22°C to a warmer threshold as ‒VVEL increases for non-thunderstorm situations
- Supercooled large droplets (SLDs, droplet diameter > 50μm) associated with severe icing is diagnosed in some NWP models

Note that the Rapid Refresh (RAP) model predicts SLD explicitly, while the Rapid Update Cycle (RUC2) model used for aviation in 2011 (the time of this case) did not.

Use T/RH/−VVEL to identify multiple layers with icing potential, separated by one or more layers with little icing risk. The model data should be validated against icing reports and other observations.

The main advantage of plan view maps and cross sections of model analyses is that they can provide information to diagnose supercooled cloud droplets, including SLDs. The Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR, 4-km grid spacing) have this capability, with hourly (to quarter-hourly for some data) output to 18 hrs. These models also have explicitly predicted cloud liquid/ice, supercooled water, and precipitation type and mass for each model layer.

The limitations primarily relate to the accuracy of the explicit cloud water and precipitation analyses and forecasts. In past verification studies, the RAP and HRRR have captured only about 40% of icing PIREPs. A new data assimilation system was implemented in the RAP and HRRR in 2014, which may improve explicit analyses and predictions of cloud condensate and precipitation, especially in convective situations over the first few hours. This will, in turn, improve model icing diagnosis in the short range (1 to 6 hours).

### Step 1: Diagnosing Locations of Icing » NWP Analyses » Vertical X-C and Plan View Maps - Data

Below are the cross section, 925-850, and 850-700 hPa plan view maps for the RUC2 analysis of layer mean T, RH, and –VVEL for 13 UTC 26 February 2011. The location of the cross section is found on the mean layer map as a horizontal line at 42°N. We are assuming that 13 UTC data would be the most current available to the daytime shift for analysis. We’ll analyze the cross section followed by the plan view maps.

#### Question 1

Circle area(s) in the cross section where icing criteria for T, RH, and –VVEL are met. (Review the Icing Flowchart)

Use the pen to circle area(s) where icing criteria for T, RH, and –VVEL are met.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The answer follows the guidelines for T (0°C to -22°C), RH (>80%), and –VVEL (> 0) for the cross section. Much of the cross section has an icing risk between the surface and 700 hPa at 13 UTC 26 February 2015.

Now we'll look for areas in the 850-700 hPa and 925-850 hPa plan view maps where icing criteria for T, RH, and –VVEL are met.

#### Question 2

Use the pen to circle area(s) in the 850-700 hPa map where the icing criteria are met.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The answer follows the guidelines for T (0° to -22°C), RH (>80%), and –VVEL (> 0) for the layer mean. We can see that a significant portion of the service area has an icing risk in this layer at 13 UTC 26 February 2015.

#### Question 3

Use the pen to circle area(s) in the 925-850 hPa plan view map where icing criteria are met.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

Even more of the service area has an icing risk in the 925 to 850 hPa layer at 13 UTC 26 February 2015, as shown by the red shading.

### Step 1: Diagnosing Locations of Icing » NWP Analyses » Model Soundings - Description

Model soundings are analysis and forecast vertical profiles of temperature T and dew point Td in each model grid column. These are useful where and when radiosonde data are unavailable. To validate model soundings, you can use nearest neighbor 00 and 12 UTC (and occasional 06 and 18 UTC) radiosonde observations, where available.

When using model soundings, do the same icing checks as for radiosondes. (Review the Icing Flowchart)

Advantages

- Fills in data gaps between radiosondes in space and time
- Can validate initial conditions by comparing to radiosonde data when available

Limitations

- Less detailed than radiosonde Skew-Ts
- Not useful if the model analysis is poor

### Step 1: Diagnosing Locations of Icing » NWP Analyses » Model Soundings - Data

#### Question

Here’s the RUC2 analysis sounding for the nearest grid column to Davenport IA (DVN). Using the same criteria you’d use for Skew-Ts, enclose the area with a risk of icing.

Use the pen to enclose the area with a risk of icing.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

An atmospheric layer from about 700 hPa to the surface is near saturation, with temperatures around -10°C. The sounding looks almost identical to the radiosonde from DVN taken at the same time. It lends more confidence to the NWP analysis near DVN and the model forecast for later forecast hours. Forecasters using BUFKIT software to plot RUC or NAM soundings can overlay vertical motion (Omega). This allows quick identification of upward vertical motion (negative Omega values) in moist layers, which correlates to higher icing potential and severity.

### Step 1: Diagnosing Locations of Icing » NWP Analyses » Current Icing Potential (CIP) - Description

The CIP combines model analysis (RUC2 in 2011, RAP in 2015) and observations into one group of products to show the current icing picture over the CONUS airspace. Five CIP products are available:

- Icing severity and supercooled large droplets (SLD) potential
- Icing severity by flight level
- Icing severity where icing probability is greater than 25%
- Icing severity where icing probability is greater than 50%
- Probability of icing

Plots are available every 2000 feet from 1000 feet above mean seal level (MSL) through FL290. Maximum value plots through this range of elevations can also be viewed. When available, icing PIREPs and AIREPs are plotted, indicating icing severity or both severity and type to help validate the analysis. For FL plots, icing reports within 1000 vertical feet of the plotted flight level are included. For maximum value plots, all icing reports are shown.

Plots of CIPs can be obtained from the aviation weather website.

The following observations are used in the CIP: lightning, PIREPs, METARs, radar, and satellite radiances. The model analysis data used in the CIP include temperature (T), relative humidity (RH), negative pressure vertical velocity (‒VVEL), and supercooled liquid water (SLW) if available.

When using the CIP, consider the quality and limitations of the observations and model analyses. Ask yourself:

- How well does the NWP model analysis validate?
- How good are the data supplementing satellite LW IR data beneath the cloud top?
- Are bad PIREPs included in the observational data, potentially affecting the CIP?
- Are PIREPs available in areas of significant icing?

### Step 1: Diagnosing Locations of Icing » NWP Analyses » Current Icing Potential (CIP) - Data

The CIP data plots below show only the maximum value for each product between FL010 through FL300, but we can use other model and observation data to fill in the FLs for icing and severity. In practice, however, we’d have 00-hour data for all FLs at 2000 foot intervals, which we could directly check for consistency with other model data and observations.

The first product, the maximum probability for icing, also plots icing reports by type and severity near report time for CIP validation. We see that by 13 UTC, the high maximum probability area contains numerous reports of light to moderate icing.

The second product, the icing severity composite, shows the highest icing severity as indicated by the color bar shading. Here, the validating icing reports show severity using digit size and value.

Finally, the maximum SLD potential product shows the locations of the highest diagnosed risk of SLDs in percent, using the RUC analysis. PIREP icing type and severity are indicated by the letter font size in accordance with the legend beneath the map.

Because SLD pose a significant threat for moderate or greater clear or mixed icing, CWSUs emphasize their presence in the analyses. Forecasters issuing Meteorological Information Statements (MISs) with icing and other significant weather outlooks for the next 12 to 18 hours will warn of significant icing risk if SLD are forecast, even with low icing probabilities. In our case, we have a high probability of SLD in northeast Kansas and northwest Missouri, not far upwind of the Chicago CWSU service area.

NOTE: If you have used the NWP analysis as part of diagnosing icing and found that it agrees with the observations, you don’t need to validate the analysis again. You can go directly to using the NWP forecast.

### Step 2: Make a First Forecast

### Step 2: Make a First Forecast » Review the Data

We’ve explored the initial data and located icing threats. Now we will make our first forecast out to 21 UTC 27 February 2011. Click the tabs and and subtabs to review the initial data annotated with the areas of actual and potential icing. Then on the next page, you will do two things: 1) mark up a map with the initial 13 UTC locations of icing and icing levels, and 2) make a first forecast based on how you expect the icing to move, annotating the advance of icing conditions at 15, 18, and 21 UTC.

### Step 2: Make a First Forecast » Make the First Forecast

#### Question 1

Now we'll describe the icing conditions as of 13 UTC 26 February 2011. In this first question, you'll identify areas of icing, then in question 2 you'll identify the flight levels and intensity for those areas.

Use the pen to enclose areas of icing at 13 UTC.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

To identify the area coverage, we used the area with a 50% or greater probability of experiencing icing from the 13 UTC analysis CIP Probability of Icing chart.

#### Question 2

(Use the selection boxes to choose the answers that best complete the statement.)

As of 13 UTC 26 February 2011, icing conditions were expected
, with
intensity.
Icing conditions were expected from the surface to FL100, with moderate intensity.

To identify the icing levels, we used the PIREPs, layer mean maps, and cross-sections, which all showed the top of the moist sub-freezing layer at about 700 hPa, or about FL100. The bottom of the icing level is at the surface over the service area. Severity was obtained from the CIP icing severity composite.

#### Question 3

Based on the initial temperature, moisture, and winds, how do you expect the icing area(s) to move over the next 8 hours? Specifically, where will the forecast forward edge of the icing extent be on 26 February at 15, 18, and 21 UTC over the service area?

Draw the forecast forward edge of the icing areas using the red pen for 15 UTC, the blue pen for 18 UTC, and the gray pen for 21 UTC.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The graphic shows a first forecast consistent with quasi-steady state atmospheric flow, with a steady advance of the initial icing area from the west-southwest to the east-northeast at 15, 18, and 21 UTC. Maintaining the icing layer from the surface to FL100 is also consistent with a steady state situation.

#### Question 4

Now enclose any areas that may be affected by SLD at 15 and 21 UTC.

Use the green pen to enclose any areas affected by SLD at 15 UTC and the gold pen for any areas affected at 21 UTC.

Tool: | Tool Size: | Color:
--- | --- | ---
Pen Eraser |  |

The CIP indicates that SLDs in northeast Kansas and northwest Missouri are about to be advected into the service area at 13 UTC. For a steady state flow regime, we draw a yellow curved line in the southwest service area straddling the Mississippi River in southeastmost Iowa, and west-central Illinois. By 21 UTC, the SLD area should reach across the entire southern 1/3 of the service area to southwestermost Michigan and northwest Indiana. This would include the Chicago O'Hare airport.

#### Question 5

Use the selection boxes to choose the answers that best complete each statement.

At 15 UTC, moderate to severe icing was expected in the
part of the Chicago CWSU service area from
to
with light to moderate icing over the
portion of the service area.

At 15 UTC, moderate to severe icing was expected in the southwest part of the Chicago CWSU service area from the surface to FL100 with light to moderate icing over the western portion of the service area.

By 21 UTC, moderate to severe icing was expected in
and light to moderate icing was expected over
from
to
.

By 21 UTC, moderate to severe icing was expected in northern Indiana and light to moderate icing was expected over Wisconsin from the surface to FL100.

Below is the final first forecast graphic with the 13 UTC 26 February 2011 icing locations enclosed by black; the forecast forward edge of icing indicated by shading enclosed by dashed lines; flight levels indicated by text; and the advance of SLD and possible moderate to severe icing shown with shading enclosed by solid lines. Areas with moderate to severe icing expected are affected by the east-northeast movement of the SLD area originally to the immediate southwest of the service area. The southeastern third of the service area was expected to be affected by 21 UTC. Other areas of the service area were expected to have light to moderate icing moving north and east from Iowa into northwest Illinois, southern Wisconsin and southern Lake Michigan by 21 UTC.

Icing FLs are determined from the initial PIREPs/AIREPs, cross-sections, and plan view maps of mean layer temperature, RH, and vertical motion. The initial icing area is established using all of the satellite, analysis, and other observation data available, which were consistent with the Current Icing Products. The forward edge of icing and of expected SLD are predicted assuming steady-state advection of conditions from west-southwest to east-northeast during the first forecast period.

This completes Step 2. We're ready for the final step, where we adjust the first forecast, if necessary, based on model guidance.

### Step 3: Use NWP Guidance to Make Adjustments, If Needed

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » Introduction

After you complete the first forecast, you use NWP forecast data to determine if it needs to be adjusted. However, another activity should be done before doing this step.

#### Question

What should you do before comparing the NWP model forecast data against the first forecast?

a) Validate the model initial conditions against the observed initial conditions
b) Determine if the PIREPs have been quality controlled
c) Find areas where cloud top temperatures are less than -22°C

The correct answer is a.

We need to validate the NWP model initial conditions before we can be confident in using its forecast guidance.

If you used the NWP analysis to diagnose areas of icing, you needed to determine the quality of NWP model initial conditions. We determined this in Step 1, and saw that the the NWP analysis was in good agreement with the observations used for icing diagnosis. Therefore, we can go directly to the next step - using the Forecast Icing Product (FIP) data to modify your first forecast, if necessary.

Options B and C are incorrect because they are performed as part of the icing analysis done in Step 2.

Please make a selection.

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » NWP Forecast Products Used for Icing Prediction

As with the initial analysis, we can use model forecast soundings and two-dimensional T/RH/-VVEL cross sections to find flight levels for moist sub-freezing layers in a potential high impact area. We can also use the layer mean T/RH/-VVEL maps to determine the areal extent of potential icing conditions.

Like CIPs, FIPs use algorithms to convert the NWP data. Once checked for consistency with the icing products above, FIPs are a more efficient way of checking the first forecast.

FIP data from the most recent RAP forecast cycle is found on the aviation weather web page, using the “Time” pull-down menu to choose 2, 3, 6, 9, 12, 15, or 18 hour forecasts.

Before we use the FIPs to determine if adjustments to the first forecast are necessary, we will do a spot check of one FIP product against the other NWP icing guidance at two valid times, 18 UTC 26 February and 00 UTC 27 February.

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » Checking FIPs Against Other Icing Forecast Guidance

We will use forecasts of 850-700 hPa and 925-850 hPa mean pressure layer T, RH and ‒VVEL to do the FIP check. Review the criteria in the Icing Flowchart. The FIPs will be for icing severity at FL050 (about 850 hPa) and FL090 (about 740 hPa).

Click the tabs and subtabs to view the products valid at each forecast time. Then answer the question below. Note that when comparing the mapped data, the FIPs cover a larger area than the mean pressure layer maps.

#### Question

Select the most accurate statement about the icing guidance provided by the NWP model and FIP data for 18 UTC 26 February and 00 UTC 27 February 2011.

a) FIP data do not agree sufficiently with the other NWP data to use the FIPs as guidance
b) FIP data agree well with the other NWP data at FL050 but not at FL090
c) FIP data agree well with the other NWP data at FL090 but not at FL050
d) FIP data agree well with the other NWP data at both FL090 and FL050

The correct answer is d.

Subjective review of the icing severity and SLD graphics for both flight levels reveals that their icing risk areas have similar locations and shapes to those in the mean layer guidance at both valid times. This can be seen in the graphics below, where areas conducive to icing are shaded in orange with outlines in red. The FL050 and FL090 icing severity graphics shown above are at about 850 and 740 hPa, at the top of the 925-850 hPa layer and near the top of the 850-700 hPa layer, respectively.

Please make a selection.

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » FIP Data for Icing Forecast

Below are the three types of FIP data (probability of icing, icing severity where probabilities are greater than 50%, and icing severity with location of SLD) from 15 UTC 26 Feb to 00 UTC 27 Feb for flight levels 050, 070, 090, and 110.

Compare the FIPs to the first forecast, looking for any changes that should be made to the first forecast icing area coverage, icing intensity, and icing levels for the CWSU service area during the forecast period. Then you will make any changes that are needed to the first forecast in the question at the bottom of the page.

#### Probability of Icing

#### Severity of Icing (Probability > 50%)

#### Severity of Icing, Risk of SLD

#### Question

Select any changes that should be made to the first forecast icing area coverage, icing intensity, and icing levels for the Chicago CWSU service area during the forecast period.

a) Adjust Illinois section of 15 UTC boundary northward to Wisconsin border
b) Remove the icing threat after 19 UTC for the service area
c) Have the icing threat completely cover the service area by 19 UTC
d) Increase lowest flight level for the icing threat to FL090 at 19 UTC
e) Increase highest flight level for the icing threat to FL120 through the forecast
f) Increase icing intensity to moderate to occasionally severe from FL100 through 120
g) Remove icing threat at all FLs over eastern Iowa and western Illinois by 19 UTC

The correct answers are a, c, e.

The icing severity chart for 15 UTC at FL070 shows moderate intensity icing north of the first forecast icing area (inside the circle).

Reviewing the 18 UTC forecasts for all FLs, we see that icing has spread into much of southern Wisconsin and southwestern lower Michigan. Moderate icing is found as high as FL110 in the northern and northeastern portions of our service area. Moderate or greater icing with areas of SLD is forecast from FL050 through FL090 in the western portions of the service area.

By 21 UTC, the entire service area is covered with at least light icing. The central portion has at least moderate icing and areas of SLD, which implies the potential for even severe clear or mixed icing. At FL110, the moderate icing is found at 18 UTC, while somewhat further north and east, it still can be found in the Wisconsin, Michigan, and Indiana portions of the service area. Meanwhile, icing conditions from FL050 through 090 in the western part of the service area remain significant, especially at FLs 050 and 070.

After taking the forecast into account and making the adjustments, your final forecast should look something like this.

A possible Met Information Statement (MIS) from 15 UTC through 19 UTC 26 February might read:

OB MIS 02 VALID 261500-262100 ...FOR ATC PLANNING PURPOSES ONLY... E Iowa/all of Illinois/NW Indiana/SW Lower Mich/SE Wisc/lower third Lk Mich.. Modt ocnl svr icing in clds and prcp blw FL100. Rest of ZAU, light to moderate icing in clds and prcp blw FL120. Modt ocnl severe icing in clds/prcp blw FL120 entire ZAU by 18Z cont beyond 21Z at and blw FL090, but impr frm sw above FL090 after 21Z.

Please make a selection.

### Step 3: Use NWP Guidance to Make Adjustments, If Needed » Case Summary

The severe icing situation that occurred in the Chicago CWSU service area on 26 February 2011 could largely be inferred from the analysis and observations, and predicted from the NWP forecast and FIP guidance.

To show what transpired during this forecast period and beyond, we will use hourly CIPs from 15 through 23 UTC 26 February overlaid with actual icing PIREP locations and severity. These are shown at hourly intervals in the animation below.

As you can see, the Chicago CWSU service area was almost completely covered by at least light icing from 15 UTC through 23 UTC. Icing intensities increased after about 17 UTC and then remained steady through 23 UTC.

Conditions did not improve after 23 UTC. In fact, a severe icing report was issued at 0043 UTC for FL030 15 miles east of KORD. In addition, a ground stop was ordered at KORD because of severe icing on one of ORD’s runways.

The RUC2 analysis sounding from KORD at 01 UTC 27 February shows a deep saturated sub-freezing (-3° to -10°C) layer from the surface to 750 hPa, with dry air above, conditions that are are consistent with severe icing. The red oval in the analysis indicates where it’s fully saturated. In the range of temperatures where snow grows rapidly at the expense of supercooled liquid water (-12° to -19°C), the atmosphere is dry. No ice crystals were expected to reduce the amount of supercooled water. It isn’t surprising that there was serious icing at KORD at this time in the air and on the ground!

### Step 2: Make a First Forecast

### Summary and References » Lesson Summary

This lesson uses a winter icing case in the Midwest to present a procedure to forecast enroute icing for aviation. It is summarized below.

First, observations and NWP analyses are evaluated to locate areas and flight levels in or near the forecast area that are currently at risk for icing. Then the consistency of the NWP analyses is reviewed by comparing them to observations. If they are similar, they can be used together to find initial icing conditions. The comparison also helps you know whether the model guidance will be useful in making the final forecast.

Next, you project current observations and model initial conditions to make a first forecast for enroute icing. If the initial icing conditions in the NWP model are consistent with the observations, the NWP forecast icing products are used to check the first forecast. The first forecast is adjusted, as needed, based on the NWP model icing forecast, and the final forecast, including flight levels and icing intensity, is made.

Many observation and analysis tools are available to guide icing forecasts at levels extending from the surface to the tropopause. The tools come from various sources, including METARs, radiosondes, aircraft pilot reports, and weather satellites.

### Summary and References » References

Bernstein, Ben C., Frank McDonough, Marcia K. Politovich, Barbara G. Brown, Thomas P. Ratvasky, Dean R. Miller, Cory A. Wolff, and Gary Cunning, 2005: Current Icing Potential: Algorithm description and comparison with aircraft observations. J. Appl. Meteor., 44, 969–986. doi: http://dx.doi.org/10.1175/JAM2246.1

National Weather Service Instruction 10-803, 2013: Support to Air Traffic Control Facilities. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service. Cited in 2014 at http://www.nws.noaa.gov/directives/sym/pd01008003curr.pdf

Wolff, Cory A., Frank McDonough, Marcia K. Politovich, and Gary M. Cunning, 2009: The Forecast Icing Product: Recent upgrades and improvement. American Institute of Aeronautics and Astronautics, 1st AIAA Atmospheric and Space Environments Conference, 22-25 June 2009, San Antonio, TX.

Ref. NTSB report

National Transportation Safety Board Safety Recommendation A-14-17 through 21, 2014: To Dr. Louis W. Uccellini, Director, National Weather Service from Mr. Christopher A. Hart, Acting Chairman, NTSB. Cited in 2015 at http://www.ntsb.gov/safety/safety-recs/_layouts/ntsb.recsearch/RecTabs.aspx.

Mireles, Mark, Pederson, K., Elford, C., 2012: Meteorological Techniques. AFWA Technical Note 98/002, Air Force Weather Agency, U.S. Air Force, Offutt Air Force Base NE 68113.

### Contributors

#### COMET Sponsors

MetEd and the COMET® Program are a part of the University Corporation for Atmospheric Research's (UCAR's) Community Programs (UCP) and are sponsored by NOAA's National Weather Service (NWS), with additional funding by:

- Bureau of Meteorology of Australia (BoM)
- Bureau of Reclamation, United States Department of the Interior
- European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)
- Meteorological Service of Canada (MSC)
- NOAA's National Environmental Satellite, Data and Information Service (NESDIS)
- NOAA's National Geodetic Survey (NGS)
- Naval Meteorology and Oceanography Command (NMOC)
- U.S. Army Corps of Engineers (USACE)

To learn more about us, please visit the COMET website.

#### Project Contributors

##### Program Manager

- Dr. Elizabeth Mulvihill Page — UCAR/COMET

##### Project Lead/Instructional Design

- Marianne Weingroff — UCAR/COMET

##### Principal Science Advisor

- Dr. William Bua – UCAR/COMET

##### Additional Science Advisors

- John Bravender - NOAA
- William Gough - NOAA
- Robb Kaczmarek - NOAA
- Liam Lynam - NOAA

##### Graphics/Animations

- Steve Deyo — UCAR/COMET
- Lindsay Johnson — UCAR/COMET, student intern
- Sylvia Quesada — UCAR/COMET
- Marianne Weingroff — UCAR/COMET

##### Multimedia Authoring/Interface Design

- Gary Pacheco — UCAR/COMET
- Marianne Weingroff — UCAR/COMET

#### COMET Staff, Fall 2015

##### Director's Office

- Dr. Rich Jeffries, Director
- Dr. Greg Byrd, Deputy Director
- Lili Francklyn, Business Development Specialist

##### Business Administration

- Dr. Elizabeth Mulvihill Page, Group Manager
- Lorrie Alberta, Administrator
- Hildy Kane, Administrative Assistant

##### IT Services

- Tim Alberta, Group Manager
- Bob Bubon, Systems Administrator
- Dolores Kiessling, Software Engineer
- Joey Rener, Student Assistant
- Malte Winkler, Software Engineer

##### Instructional and Media Services

- Bruce Muller, Group Manager
- Dr. Alan Bol, Scientist/Instructional Designer
- Steve Deyo, Graphic and 3D Designer
- Lon Goldstein, Instructional Designer
- Bryan Guarente, Instructional Designer
- Vickie Johnson, Instructional Designer (Casual)
- Gary Pacheco, Web Designer and Developer
- Sylvia Quesada, Intern
- Sarah Ross-Lazarov, Instructional Designer (Casual)
- Tsvetomir Ross-Lazarov, Instructional Designer
- David Russi, Spanish Translations
- Andrea Smith, Meteorologist/Instructional Designer
- Marianne Weingroff, Instructional Designer

##### Science Group

- Wendy Schreiber-Abshire, Group Manager
- Paula Brown, Visiting Meteorologist, CIRA/Colorado State University
- Dr. William Bua, Meteorologist
- Dr. Frank Bub, Oceanographer (Casual)
- Lis Cohen, Meteorologist (Casual)
- Patrick Dills, Meteorologist
- Matthew Kelsch, Hydrometeorologist
- Dr. Elizabeth Mulvihill Page, Meteorologist
- Amy Stevermer, Meteorologist
- Vanessa Vincente, Visiting Meteorologist, CIRA/Colorado State University