LOOP                                                                            
ERAS                                                                            
TXTH --------------------------------------------------------------             
TXTI                 Diagnosing Severe Weather Potential          -             
TXTJ                    Using Numerical Model Outputs             -             
TXTK                                                              -             
TXTL                          Ralph A. Petersen                   -             
TXTM                    NWS/NMC/Development Division              -             
TXTN --------------------------------------------------------------             
5SEC                                                                            
TXT3 ---------------------------------------    .                               
TXT4 At 00Z 23 March 1991, unforecast      -                                    
TXT5 severe weather damaged central        -                                    
TXT6 Tennessee.  The paper shows how       -                                    
TXT7 key indicators of the potential       -                                    
TXT8 for severe weather could have been    -                                    
TXT9 inferred through manipulation of      -                                    
TXTA gridded model output, even though     -                                    
TXTB the standard level outputs from the   -                                    
TXTC 12Z March 22 run of the RAFS showed   -                                    
TXTD little sign of convection.            -                                    
TXTE ---------------------------------------                                    
9SEC                                                                            
AREA 0 0 0                                                                      
5SEC                                                                            
THCK C100&PMSL CIN4  F00                                                        
TXT3 ---------------------------------------    .                               
TXT4 The convection was associated with    -                                    
TXT5 the development and movement of a     -                                    
TXT6 major surface cyclone which formed    -                                    
TXT7 in the central plains and translated  -                                    
TXT8 slowly across the Great Lakes.        -                                    
TXT9                12Z 22 MARCH 1991 MSLP -                                    
TXTA ---------------------------------------                                    
9SEC                                                                            
THCK C100&PMSL CIN4  F12                                                        
TXT3 ---------------------------------------    .                               
TXT4 The convection was associated with    -                                    
TXT5 the development and movement of a     -                                    
TXT6 major surface cyclone which formed    -                                    
TXT7 in the central plains and translated  -                                    
TXT8 slowly across the Great Lakes.        -                                    
TXT9                00Z 23 MARCH 1991 MSLP -                                    
TXTA ---------------------------------------                                    
7SEC                                                                            
THCK C100&PMSL CIN4  F24                                                        
TXT3 ---------------------------------------    .                               
TXT4 The convection was associated with    -                                    
TXT5 the development and movement of a     -                                    
TXT6 major surface cyclone which formed    -                                    
TXT7 in the central plains and translated  -                                    
TXT8 slowly across the Great Lakes.        -                                    
TXT9                12Z 23 MARCH 1991 MSLP -                                    
TXTA ---------------------------------------                                    
7SEC                                                                            
THCK C100&PMSL CIN4  F36                                                        
TXT3 ---------------------------------------    .                               
TXT4 Note that the displays and diagnostic -                                    
TXT5 computations shown here are all being -                                    
TXT6 generated in real time on the PC      -                                    
TXT7 directly from model forecast grid     -                                    
TXT8 point data.                           -                                    
TXT9                00Z 24 MARCH 1991 MSLP -                                    
TXTA ---------------------------------------                                    
7SEC                                                                            
THCK C100&PMSL CIN4  F48                                                        
TXT3 ---------------------------------------    .                               
TXT4 Note that the displays and diagnostic -                                    
TXT5 computations shown here are all being -                                    
TXT6 generated in real time on the PC      -                                    
TXT7 directly from model forecast grid     -                                    
TXT8 point data.                           -                                    
TXT9                12Z 24 MARCH 1991 MSLP -                                    
TXTA ---------------------------------------                                    
AREA 39 98 20                                                             
5SEC                                                                            
CI.2 TPCI F12                                                                   
TXT3 ---------------------------------------    .                               
TXT4 The 12 hour accumulated precipitation -                                    
TXT5 forecast valid from the 12Z 22 March  -                                    
TXT6 RAFS showed a maximum of precipitation-                                    
TXT7 along the Mississippi Valley,         -                                    
TXT8 with little rainfall forecast         -                                    
TXT9 over central Tennessee.               -                                    
TXTA ---------------------------------------                                    
9SEC                                                                            
LOOP                                                                            
CINX LIFT F12                                                                   
TXT3 ---------------------------------------    .                               
TXT4 Likewise, the 12 hour Lifted Index    -                                    
TXT5 forecast from the 12Z 22 March RAFS   -                                    
TXT6 showed a region of weak stability     -                                    
TXT7 in the area of forecast precipitation,-                                    
TXT8 but relatively stable values over     -                                    
TXT9 Tennessee at 00Z.                     -                                    
TXTA ---------------------------------------                                    
9SEC                                                                            
LOOP                                                                            
MIXR  850                                                                       
TXT3 ----------------------------------         .                               
TXT4 The 850 mb Mixing Ratio forecast -                                         
TXT5 for 00Z showed a maximum of      -                                         
TXT6 moisture over Southern Illinois. -                                         
TXT7 ----------------------------------                                         
5SEC                                                                            
WIND BARB&                                                                      
TXT3 ----------------------------------         .                               
TXT4 The 850 mb Mixing Ratio forecast -                                         
TXT5 for 00Z showed a maximum of      -                                         
TXT6 moisture over Southern Illinois. -                                         
TXT7                                  -                                         
TXT8 Winds in the warm sector of the  -                                         
TXT9 cyclone were from the south, with-                                         
TXTA the largest shears along the     -                                         
TXTB warm and cold fronts.            -                                         
TXTC ----------------------------------                                         
5SEC                                                                            
CLR3 SDVR MIXR WIND&                                                            
TXT3 ----------------------------------         .                               
TXT4 The 850 mb Mixing Ratio forecast -                                         
TXT5 for 00Z showed a maximum of      -                                         
TXT6 moisture over Southern Illinois. -                                         
TXT7                                  -                                         
TXT8 Winds in the warm sector of the  -                                         
TXT9 cyclone were from the south, with-                                         
TXTA the largest shears along the     -                                         
TXTB warm and cold fronts.            -                                         
TXTC                                  -                                         
TXTD This combination resulted in a   -                                         
TXTE maximum moisture flux convergence-                                         
TXTF over northern Illinois, in the   -                                         
TXTG area of heavy precip., but well  -                                         
TXTH away from the convective outbreak-                                         
TXTI ----------------------------------                                         
XSCT 45 100 30 85                                                               
AREA 39 98 20                                                             
PLAN                                                                            
5SEC                                                                            
WSPD&AROW WIND&HGHT  300                                                        
TXT3 ----------------------------------         .                               
TXT4 Aloft, the 300 mb flow showed a  -                                         
TXT5 jet streak approaching the       -                                         
TXT6 Mississippi Valley, with an exit -                                         
TXT7 region encroaching upon the area -                                         
TXT8 of observed convection.          -                                         
TXT9 ----------------------------------                                         
7SEC                                                                            
TXT9                                  -                                         
TXTA A cross-section along the line   -                                         
TXTB through the exit region of the   -                                         
TXTC jet streak reveals more detail   -                                         
TXTD about the frontal structures and -                                         
TXTE low-level moisture regimes.      -                                         
TXTF ----------------------------------                                         
9SEC                                                                            
CROS                                                                            
CLR2 THTA                                                                       
CIN5 LATT CLRF&                                                                 
CINX PRES CLRF&                                                                 
CLR1 WSPD&                                                                      
TXT3 ----------------------------------         .                               
TXT4 The potential temperature field  -                                         
TXT5 shows a deep baroclinic zone     -                                         
TXT6 supporting the jet streak, above -                                         
TXT7 a surface front separating a     -                                         
TXT8 polar cold dome from the warmer  -                                         
TXT9 air to the south.                -                                         
TXTA ----------------------------------                                         
7SEC                                                                            
CLR3 MIXR&                                                                      
TXT3 ----------------------------------         .                               
TXT4 The potential temperature field  -                                         
TXT5 shows a deep baroclinic zone     -                                         
TXT6 supporting the jet streak, above -                                         
TXT7 a surface front separating a     -                                         
TXT8 polar cold dome from the warmer  -                                         
TXT9 air to the south.                -                                         
TXTA                                  -                                         
TXTB The low level moisture supply    -                                         
TXTC is confined primarily to the     -                                         
TXTD south of the surface front.      -                                         
TXTE ----------------------------------                                         
9SEC                                                                            
TXT3 ----------------------------------         .                               
TXT4 The potential temperature field  -                                         
TXT5 shows a deep baroclinic zone     -                                         
TXT6 supporting the jet streak, above -                                         
TXT7 a surface front separating a     -                                         
TXT8 polar cold dome from the warmer  -                                         
TXT9 air to the south.                -                                         
TXTA                                  -                                         
TXTB The low level moisture supply    -                                         
TXTC is confined primarily to the     -                                         
TXTD south of the surface front.      -                                         
TXTE                                  -                                         
TXTF To study the effects of adiabatic-                                         
TXTG flow on this low level moisture, -                                         
TXTH several low level isentropic     -                                         
TXTI were derived from the standard   -                                         
TXTJ level gridded model output.      -                                         
TXTK ----------------------------------                                         
9SEC                                                                            
PLAN                                                                            
PRES SLYR I305 I300 SLVL I300                                                   
TXT3 ----------------------------------         .                               
TXT4 To assess the effects of low-level                                         
TXT5 processes on the creation of an  -                                         
TXT6 environment conducive for        -                                         
TXT7 severe convection (i.e., one with-                                         
TXT8 a localized increase in low-level-                                         
TXT9 moisture and a lifting mechanism)-                                         
TXTA the 300 and 305 K isentropic     -                                         
TXTB surfaces were selected.  These   -                                         
TXTC levels define the bottom and top -                                         
TXTD of the boundary layer in the     -                                         
TXTE cyclone's warm sector.           -                                         
TXTF               300 K Pressure --> -                                         
TXTG ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
CLR3 MIXR&CLR2 WIND&                                                            
TXT3 ----------------------------------         .                               
TXT4 Inclusion on the moisture and    -                                         
TXT5 wind forecast data for 00Z shows -                                         
TXT6 a well defined moisture supply   -                                         
TXT7 emanating from the Gulf of Mexico.                                         
TXT8 Although the winds on the lower  -                                         
TXT9 isentropic surface are weaker    -                                         
TXTA than at 850 mb, the source of    -                                         
TXTB the low-level moisture and the   -                                         
TXTC primary areas of moisture        -                                         
TXTD transport are readily apparent,  -                                         
TXTE moving toward the weak surface   -                                         
TXTF frontal zone across Tennessee.   -                                         
TXTG ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
TXT3 ----------------------------------         .                               
TXT4 The total volume of moisture     -                                         
TXT5 being transported northward in   -                                         
TXT6 the isentropic boundary layer,   -                                         
TXT7 however, depends not only on the -                                         
TXT8 mean mixing ratio and mean wind  -                                         
TXT9 in the layer, but also the static-                                         
TXTA stability, which in turn         -                                         
TXTB provides a measure of the mass   -                                         
TXTC of air holding moisture in the   -                                         
TXTD layer.                           -                                         
TXTE                                  -                                         
TXTF                                  -                                         
TXTG ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
PRES LDIF                                                                       
TXT3 ----------------------------------         .                               
TXT4 The weakest static stability (and-                                         
TXT5 correspondingly largest mass) in -                                         
TXT6 the isentropic boundary layer    -                                         
TXT7 is clearly isolated in the region-                                         
TXT8 strongest diurnal heating over   -                                         
TXT9 Mississippi, with nearby minima  -                                         
TXTA associated with the fronts,      -                                         
TXTB both to the west over Texas and       -                                    
TXTC to the north over Kentucky and   -                                         
TXTD Tennessee.                       -                                         
TXTE ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
PRES                                                                            
TXT3 ----------------------------------         .                               
TXT4 When the mixing ratio and mass   -                                         
TXT5 fields are combined to produce   -                                         
TXT6 the total moisture in the layer, -                                         
TXT7 a distinct maximum of moisture   -                                         
TXT8 is apparent above the lower      -                                         
TXT9 isentropic surface.              -                                         
TXTA ----------------------------------                                         
SMLT MIXR LAVE PRES LDIF&                                                       
TXT3 ----------------------------------         .                               
TXT4 When the mixing ratio and mass   -                                         
TXT5 fields are combined to produce   -                                         
TXT6 the total moisture in the layer, -                                         
TXT7 a distinct maximum of moisture   -                                         
TXT8 is apparent above the lower      -                                         
TXT9 isentropic surface.              -                                         
TXTA ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
CLRF WIND LAVE&                                                                 
TXT3 ----------------------------------         .                               
TXT4 When the mixing ratio and mass   -                                         
TXT5 fields are combined to produce   -                                         
TXT6 the total moisture in the layer, -                                         
TXT7 a distinct maximum of moisture   -                                         
TXT8 is apparent above the lower      -                                         
TXT9 isentropic surface.              -                                         
TXTA                                  -                                         
TXTB Although the average winds in the-                                         
TXTC layer are still relatively weak  -                                         
TXTD over this area,                  -                                         
TXTE ----------------------------------                                         
7SEC                                                                            
CLR4 FLUX SMLT MIXR LAVE PRES LDIF WIND LAVE&                                   
TXT3 ----------------------------------         .                               
TXT4 When the mixing ratio and mass   -                                         
TXT5 fields are combined to produce   -                                         
TXT6 the total moisture in the layer, -                                         
TXT7 a distinct maximum of moisture   -                                         
TXT8 is apparent above the lower      -                                         
TXT9 isentropic surface.              -                                         
TXTA                                  -                                         
TXTB Although the average winds in the-                                         
TXTC layer are still relatively weak  -                                         
TXTD in the moist area,               -                                         
TXTE                   the low-level  -                                         
TXTF adiabatic moisture transport in  -                                         
TXTG the cyclones warm sector (the    -                                         
TXTH product of the wind and total    -                                         
TXTI moisture content) is exceeding   -                                         
TXTJ strong, again with variations    -                                         
TXTK along the warm front in Tennessee.                                         
TXTL ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
FLUX SMLT MIXR LAVE PRES LDIF WIND LAVE                                         
TXT3 ----------------------------------         .                               
TXT4 When the adiabatic moisture flux -                                         
TXT5 convergence is computed from the -                                         
TXT6 moisture transport grid, a clear -                                         
TXT7 signal of localized low-level    -                                         
TXT8 moisture increase is apparent    -                                         
TXT9 in the area of convection.       -                                         
TXTA ----------------------------------                                         
CLR4 DVRG FLUX SMLT MIXR LAVE PRES LDIF WIND LAVE&                              
TXT3 ----------------------------------         .                               
TXT4 When the adiabatic moisture flux -                                         
TXT5 convergence is computed from the -                                         
TXT6 moisture transport grid, a clear -                                         
TXT7 signal of localized low-level    -                                         
TXT8 moisture increase is apparent    -                                         
TXT9 in the area of convection.       -                                         
TXTA ----------------------------------                                         
9SEC                                                                            
9SEC                                                                            
FLUX SMLT MIXR LAVE PRES LDIF WIND LAVE                                         
TXT3 ----------------------------------         .                               
TXT4 When the adiabatic moisture flux -                                         
TXT5 convergence is computed from the -                                         
TXT6 moisture transport grid, a clear -                                         
TXT7 signal of localized low-level    -                                         
TXT8 moisture increase is apparent    -                                         
TXT9 in the area of convection.       -                                         
TXTA                                  -                                         
TXTB                                  -                                         
TXTC If the data a manipulated further-                                         
TXTD to combine the regions of moisture                                         
TXTE convergence and the areas where  -                                         
TXTF adiabatic ascent is diagnoses    -                                         
TXTG along the lower isentropic       -                                         
TXTH surface, the forecast potential  -                                         
TXTI is further reinforced.           -                                         
TXTJ ----------------------------------                                         
PRES&                                                                           
SMLT ZNEG ADVT PRES WIND ZPOS DVRG FLUX SMLT MIXR LAVE PRES LDIF WIND LAVE&     
TXT3 ----------------------------------         .                               
TXT4 When the adiabatic moisture flux -                                         
TXT5 convergence is computed from the -                                         
TXT6 moisture transport grid, a clear -                                         
TXT7 signal of localized low-level    -                                         
TXT8 moisture increase is apparent    -                                         
TXT9 in the area of convection.       -                                         
TXTA                                  -                                         
TXTB                                  -                                         
TXTC If the data a manipulated further-                                         
TXTD to combine the regions of moisture                                         
TXTE convergence and the areas where  -                                         
TXTF adiabatic ascent is diagnoses    -                                         
TXTG along the lower isentropic       -                                         
TXTH surface, the forecast potential  -                                         
TXTI is further reinforced.           -                                         
TXTJ ----------------------------------                                         
9SEC                                                                            
TXT4                                  -                                         
TXT5                                  -                                         
TXT6                                  -                                         
TXT7                                  -                                         
TXT8                                  -                                         
TXT9                                  -                                         
TXTA                                  -                                         
TXT4 It becomes clear that even though-                                         
TXT5 the forecast model did not       -                                         
TXT6 precipitate in the area of severe-                                         
TXT7 convection, the fine-scale       -                                         
TXT8 convective destabilization was   -                                         
TXT9 correctly forecast and apparent if                                         
TXTA diagnosed properly.              -                                         
TXTB  - - - - - - - - - - - - - - -   -                                         
9SEC                                                                            
9SEC                                                                            
9SEC                                                                            
TXT3 ----------------------------------         .                               
TXT4                                  -                                         
TXT5                                  -                                         
TXT6                                  -                                         
TXT7                                  -                                         
TXT8     TO REPEAT DEMO, TYPE         -                                         
TXT9                                  -                                         
TXTA                                  -                                         
TXTB            FCST.                 -                                         
TXTC                                  -                                         
TXTD                                  -                                         
TXTE                                  -                                         
TXTF                                  -                                         
TXTG                                  -                                         
TXTH                                  -                                         
TXTI                                  -                                         
TXTJ ----------------------------------                                         
                                                                                
                                                                                
