910  
ACUS11 KWNS 090908  
SWOMCD  
SPC MCD 090908  
MIZ000-OHZ000-INZ000-ILZ000-WIZ000-IAZ000-091515-  
 
MESOSCALE DISCUSSION 0062  
NWS STORM PREDICTION CENTER NORMAN OK  
0308 AM CST FRI FEB 09 2018  
 
AREAS AFFECTED...PORTIONS OF FAR EASTERN IOWA TO SOUTHERN MICHIGAN  
 
CONCERNING...HEAVY SNOW  
 
VALID 090908Z - 091515Z  
 
SUMMARY...MODERATE TO LOCALLY HEAVY SNOW, WITH RATES UP TO ONE INCH  
PER HOUR, WILL CONTINUE EXPANDING EASTWARD THIS MORNING.  
 
DISCUSSION...ON THE NOSE OF STRONGER 850-700MB WARM ADVECTION AND  
RELATED ISENTROPIC ASCENT, MODERATE SNOWFALL HAS ADVANCED EASTWARD  
INTO PORTIONS OF NORTHERN INDIANA AND SOUTHERN MICHIGAN EARLY THIS  
MORNING. FORECAST SOUNDINGS DEPICT ASCENT THROUGH A DENDRITIC-GROWTH  
LAYER SEVERAL THOUSAND FEET DEEP. THEREFORE, WHILE UPWARD VERTICAL  
MOTION IS NOT PARTICULARLY ROBUST, RELATIVELY EFFICIENT CRYSTAL  
GROWTH SHOULD COMPENSATE SOMEWHAT, YIELDING RATES AROUND 0.5-1 INCH  
PER HOUR THIS MORNING.  
 
FARTHER WEST INTO NORTHERN ILLINOIS, THE STRONGEST UPWARD MOTION  
RELATED TO WARM ADVECTION HAS GENERALLY REMAINED AT TEMPERATURE  
LEVELS TOO WARM FOR DENDRITIC GROWTH, LIMITING SNOWFALL RATES.  
HOWEVER, LIKELY RELATED TO INCREASING 700-MB CONFLUENCE AND  
ASSOCIATED FRONTOGENETIC CIRCULATIONS, A NARROW BAND OF HIGHER  
REFLECTIVITY (SUGGESTING AN INCREASE IN SNOW AGGREGATION) HAS  
ORGANIZED OVER NORTHERN ILLINOIS. ASCENT ASSOCIATED WITH THIS BAND  
EXISTS AT COLDER TEMPERATURES, IN TURN FAVORING MORE EFFICIENT  
CRYSTAL PRODUCTION. SUPPORTING THIS NOTION, KDVN/QUAD CITIES 88D  
DATA HIGHLIGHT SUBTLE ENHANCEMENTS IN KDP (0.2-0.4 DEG/KM) AROUND  
11-13K FT AGL, WHICH IS CONSISTENT WITH AN INCREASE IN  
PLANAR/DENDRITIC CRYSTAL GROWTH. THIS NARROW BAND WILL SLOWLY SHIFT  
EAST THIS MORNING, BUT WILL LIKELY BE POSITIONED OVER NORTHERN  
ILLINOIS OVER THE NEXT SEVERAL HOURS, POTENTIALLY IMPACTING THE  
MORNING RUSH HOUR WITH LOCALIZED SNOWFALL RATES UP TO ONE INCH PER  
HOUR.  
 
..PICCA.. 02/09/2018  
   
..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...DTX...IWX...GRR...LOT...MKX...DVN...  
 
LAT...LON 41619151 42249045 42618839 42838563 42768449 42678370  
42238329 41918348 41728408 41398589 41428878 41459061  
41389115 41399149 41619151  
 
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