LOOP                                                                            
ERAS                                                                            
TXT3 ---------------------------------------------------------------             
TXT4        PREVIOUS ANALYSIS / CURRENT FORECAST COMPARISONS       -
TXT5 ---------------------------------------------------------------             
4SEC                                                                            
TXT9 -------------------------------------------------------------------------- 
TXTA This menu is intended to allow forecasters to compare previous analyses  -
TXTB with future forecasts for any model data to establish atmospheric trends.-
TXTC The comparisons will be made between the 0000 UTC analysis of the        -
TXTD previous day and the 12h forecast off the 1200 UTC run of the current    -
TXTE day (valid 0000 UTC).  This will allow you to determine trends in        -
TXTF atmospheric variables by removing diurnal biases.                        -
TXTG                                                                          -
TXTH This type of analysis is particularly useful during summer when          -
TXTI deviations in various fields on a day to day basis become critical to    -
TXTJ weather forecasts.                                                       -
TXTK                                                                          -
TXTL                                 <RETURN>                                 -   
TXTM --------------------------------------------------------------------------
ENDL
loop
temp grtn 400
eras
TXT4 --------------------------------------------------------------------------                                                          -
TXT5 IN ORDER TO RUN THESE MACROS YOU MUST:                                   -
TXT6                                                                          -
TXT7 1) LOAD TWO (2) FILES FOR A PARTICULAR MODEL (NGM/NAM/GFS)               -
TXT8          It is suggested that you load two files for comparison purposes -
TXT9          when using this menu.  It is best to load the 1200 UTC model    -
TXTA          from the current day with the previous 0000 UTC run of the      -
TXTB          previous period.  (eg 1200 UTC 15 April and 0000 UTC 15 April). -
TXTC                                                                          -
TXTD          When you entered WINGRIDDS, you entered a file name, likely     -
TXTE          the most recent file.  If this was an NGM file, you may compare -
TXTF          it with the PREVIOUS NGM file by loading it in FILE 2.  To      -
TXTG          do this, use the "OPEN" command from the WINGRIDDS command line.-      
TXTH          (eg. OPEN FIL2 <RETURN>, AP199300.NGM will load the NGM file    -
TXTI          from 19 April 1993, 0000 UTC in file2).  Once both files are    -
TXTJ          loaded...type "FILS".  A list of files will appear.  The NGM    -
TXTK          data file for the current time (most recent run) should be in   -
TXTL          File 1 with the previous run (T-12) in File 2.                  -
TXTM                                                                          -
TXTN          *** IT IS IMPORTANT THAT THE MOST RECENT NGM FILE BE LOADED     -
TXTO              IN FILE 1 AND THE PREVIOUS NGM FILE IN FILE 2 SINCE         -
TXTP              SINCE DIFFERENCES WILL BE TAKEN WITH RESPECT TO FILE        -
TXTQ              NUMBERS AND NOT FILE NAMES ***                              -
TXTR                                                                          -
TXTS                                   <RETURN>                               -
TXTT --------------------------------------------------------------------------
ENDL
LOOP
TXT4 --------------------------------------------------------------------------
TXT5                                                                          -
TXT6 2) DIFFERENCES ARE COMPUTED AS FORECAST MINUS ANALYSIS                   -
TXT7          All differences are computed as NGM FORECAST MINUS PREVIOUS     -
TXT8          ANALYSIS.  The 12 hour forecast off the current run is          -
TXT9          subtracted from the 0000 UTC analysis off the previous forecast -
TXTA          run.  Hence, if you wish to examine the 500 mb height field     -
TXTB          difference over the 24 hour period from last night to this      -
TXTC          evening, select MENU OPTION 1.  The 500 mb height analysis from -
TXTD          the previous run will be displayed followed by the 500 mb       -
TXTE          height field for the 12 h forecast off the 1200 UTC run.  This  -
TXTF          enables you to compare an analysis at 0000 UTC yesterday with   -
TXTG          an expected similar field at 0000 UTC today.                    -
TXTH                                                                          -
TXTI          The difference between the periods is computed as forecast minus-
TXTJ          analysis and is displyaed.  Using this convention, we will      - 
TXTK          observe diurnal changes in various fields.  For example if the  -
TXTL          500 mb heights were analyzed at 5820 gpm at 0000 UTC and are    -
TXTM          forecast to be 5760 gpm at 0000 UTC tonight (12h forecast off   -
TXTN          the 1200 UTC model run), the difference (5760 - 5820) = -60 gpm,-
TXTO          represents the change in the height field over a 24 h period    -
TXTP          using only a 12h model forecast.  In this case -60 gpm is a     -
TXTQ          height fall of 60 gpm since the previous analysis.              -
TXTR                                                                          -
TXTS                                    <RETURN>                              -
TXTT --------------------------------------------------------------------------
ENDL
LOOP
LOOP
ERAS
TXT4 ---------------------------------------------------------------------
TXT5 THE PURPOSE OF THIS MENU IS TO ALLOW FORECASTERS TO COMPARE         -
TXT6 MODEL OUTPUT BETWEEN THE PREVIOUS ANALYSES AND SHORT TERM FORECASTS -
TXT7 TO INFER ATMOSPHERIC CHANGES/TRENDS BY REMOVING DIURNAL BIASES      -
TXT8 ---------------------------------------------------------------------
ENDL
