086  
ACUS11 KWNS 052258  
SWOMCD  
SPC MCD 052257  
INZ000-ILZ000-IAZ000-MOZ000-060300-  
 
MESOSCALE DISCUSSION 0049  
NWS STORM PREDICTION CENTER NORMAN OK  
0457 PM CST MON FEB 05 2018  
 
AREAS AFFECTED...PORTIONS OF FAR SOUTHEASTERN IOWA INTO NORTHERN  
INDIANA  
 
CONCERNING...HEAVY SNOW  
 
VALID 052257Z - 060300Z  
 
SUMMARY...MODERATE TO OCCASIONALLY HEAVY SNOW WILL CONTINUE ACROSS  
PARTS OF NORTHERN ILLINOIS INTO NORTHERN INDIANA FOR A FEW MORE  
HOURS. RATES UP TO ONE INCH PER HOUR WILL BE POSSIBLE.  
 
DISCUSSION...REGIONAL RADAR DATA HIGHLIGHT A PROGRESSIVE, BUT  
ORGANIZED BAND OF SNOWFALL EXTENDING FROM SOUTHEASTERN IOWA INTO  
NORTHWESTERN INDIANA LATE THIS AFTERNOON. SATELLITE AND RADAR DATA  
SUGGEST THAT ISENTROPIC ASCENT WITHIN THE 700-500MB LAYER IS  
FOSTERING EFFICIENT ICE-CRYSTAL PRODUCTION ALOFT, AND FORECAST  
SOUNDINGS INDICATE THAT MODEST AGGREGATION PROCESSES MAY ALSO BE  
AUGMENTING SNOWFALL RATES. THESE CONCLUSIONS ARE CONSISTENT WITH  
RADAR CROSS-SECTIONS SHOWING AN INCREASE IN REFLECTIVITY AND  
DECREASE IN DIFFERENTIAL REFLECTIVITY IN THE DIRECTION TOWARDS  
GROUND (WITHIN THE HEAVIEST PARTS OF THE BAND). ADDITIONALLY, WHILE  
THE DENDRITIC GROWTH LAYER IS NOT PARTICULARLY DEEP (SOMEWHAT  
LIMITING RATES), ADEQUATE ASCENT ABOVE 700MB IS FAVORABLE FOR  
DENDRITIC/PLANAR CRYSTALS, AND MODEST ENHANCEMENTS IN KDP ARE NOTED  
AROUND 12-17K FT. THIS MICROPHYSICAL PROFILE SHOULD CONTINUE TO  
YIELD SNOWFALL RATES UP TO ONE INCH PER HOUR AS THE BAND ADVANCES  
EAST. HOWEVER, RATES SHOULD GRADUALLY DIMINISH LATER THIS EVENING  
AND WITH EASTWARD EXTENT, OWING TO A DECREASE IN ASCENT WITHIN THE  
-10 TO -20 C LAYER.  
 
..PICCA.. 02/05/2018  
   
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...IWX...IND...LOT...ILX...LSX...DVN...  
 
LAT...LON 40439146 41029182 41309184 41669159 41939096 41848935  
41648837 41168669 40948628 40538648 40008916 40149077  
40319145 40439146  
 
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