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Mesoscale Discussion 27
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   MESOSCALE DISCUSSION 0027
   NWS STORM PREDICTION CENTER NORMAN OK
   1225 PM CST MON JAN 05 2015

   AREAS AFFECTED...PORTIONS OF SOUTHEAST SOUTH DAKOTA...SOUTHERN
   MINNESOTA...IOWA...FAR WESTERN ILLINOIS

   CONCERNING...HEAVY SNOW 

   VALID 051825Z - 060030Z

   SUMMARY...HEAVY SNOW WITH RATES OF 1.0 TO 1.5 INCHES PER HOUR WILL
   SPREAD ESEWD ACROSS PORTIONS OF THE UPPER MIDWEST AND MIDDLE
   MISSISSIPPI VALLEY THIS AFTERNOON INTO THE EARLY EVENING.

   DISCUSSION...THE LATEST SFC ANALYSIS PLACES A 1014-MB LOW NEAR THE
   MT/SD BORDER...WITH A WELL-DEFINED...QUASI-STATIONARY BOUNDARY
   EXTENDING SEWD ACROSS SD AND FARTHER SE INTO THE MIDDLE MISSOURI
   VALLEY. DIURNAL HEATING OF THE COLD/DRY AIR MASS S OF THE BOUNDARY
   IS STEEPENING LAPSE RATES IN A SHALLOW...NEAR-SFC LAYER ON THE
   RELATIVELY WARMER SIDE OF THE FRONT. WITH ADDITIONAL DIABATIC
   HEATING DURING THE NEXT FEW HOURS FURTHER REDUCING LOW-LEVEL STATIC
   STABILITY...THIS TRANSLATES TO /1/ INCREASED PROPORTION OF
   WAA-RELATED RESPONSE DISTRIBUTED TO ISENTROPIC ASCENT ATOP THE
   SLOPING FRONT...AND /2/ BOLSTERED SFC CYCLOGENESIS AS A
   LOW-STATIC-STABILITY-ENHANCED GEOSTROPHIC-ADJUSTMENT RESPONSE TO
   DCVA PRECEDING A MIDLEVEL SHORTWAVE IMPULSE NOW CROSSING THE NRN
   HIGH PLAINS PER MOISTURE-CHANNEL IMAGERY. WITH A CORRESPONDING
   INCREASE IN LOW/MID-LEVEL ASCENT...ESPECIALLY AS AN 850-700-MB
   FRONTOGENETIC BAND BECOMES ESTABLISHED ACROSS THE DISCUSSION AREA
   DURING THE NEXT FEW HOURS...SNOW WILL SPREAD ACROSS THE REGION THIS
   AFTERNOON AND BECOME HEAVY.

   THE 12Z OAX AND MPX RAOBS SUGGEST THAT THE BULK OF THE THERMODYNAMIC
   PROFILE REMAINS BELOW -10C...YIELDING SHALLOW/LOW-LEVEL DENDRITIC
   GROWTH ZONES BENEATH STRONGER ASCENT. REGARDLESS...SUCH COLD
   PROFILES WILL SUPPORT HIGH SNOW-TO-LIQUID RATIOS...WITH RECENT SREF
   OUTPUT SUGGESTING 15:1 TO PERHAPS AS HIGH AS 25:1 RATIOS ACROSS THE
   REGION. THIS WILL TRANSLATE TO SEVERAL HOURS OF 1.0-1.5-INCH/HOUR
   SNOWFALL RATES SPREADING ESEWD ACROSS THE AREA...ESPECIALLY AFTER
   20Z/21Z.

   THE HEAVIEST SNOW IS ANTICIPATED IN A 50-60-MILE-WIDE CORRIDOR
   CENTERED ALONG A LINE FROM 30 SSE SIOUX FALLS SD TO 25 NNE DES
   MOINES IA TO 15 NNW PEORIA ILLINOIS. THIS INCLUDES AREAS NEAR...AND
   PARTICULARLY NORTH OF...THE DES MOINES IA AREA. BY EARLY
   EVENING...THE HEAVIER SNOW WILL BE SHIFTING ESE OF THE MS
   RIVER...WITH SNOWFALL DECREASING IN COVERAGE AND INTENSITY ACROSS
   THE DISCUSSION AREA FROM WNW TO ESE THROUGH THE EVENING.

   ..COHEN.. 01/05/2015


   ATTN...WFO...LOT...ILX...DVN...ARX...MPX...DMX...FSD...

   LAT...LON   43889771 44329646 43489288 42419053 42038984 41478940
               40858990 40659137 41229326 42919678 43889771 

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Page last modified: January 06, 2015
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