MESOSCALE DISCUSSION 1987
   NWS STORM PREDICTION CENTER NORMAN OK
   0151 PM CST FRI NOV 20 2015

   AREAS AFFECTED...IA...FAR NERN NEB

   CONCERNING...HEAVY SNOW 

   VALID 201951Z - 210045Z

   SUMMARY...A SWATH OF HEAVY SNOW WITH RATES OF 1-2 IN/HR WILL LIKELY
   SHIFT EAST-SOUTHEAST ACROSS A LARGE PART OF IA INTO THIS EVENING.

   DISCUSSION...MODERATE TO HEAVY SNOW IS ONGOING FROM NERN NEB ACROSS
   SIOUXLAND INTO N-CNTRL IA. LEADING PORTION OF THE HEAVY SNOW
   APPEARED TO COINCIDE WELL WITH 700-MB FRONTOGENESIS SUPPORTING
   INTENSE RATES OF 2-3 IN/HR EARLIER TODAY NEAR SIOUX FALLS. WHILE
   REFLECTIVITY HAS BEEN SOMEWHAT SUBDUED OVER THE PAST COUPLE HOURS AS
   THE 700-MB FRONTOGENESIS HAS SHIFTED NE...MID-LEVEL DCVA DOWNSTREAM
   OF A SHORTWAVE IMPULSE OVER CNTRL NEB IS YIELDING A MERGER OF HEAVY
   SNOW BANDS ACROSS SIOUXLAND. ASCENT TIED TO THE DCVA AND LOW-LEVEL
   ISENTROPIC LIFT SHOULD FOSTER A BROAD SWATH OF HEAVY SNOW THROUGH
   EARLY EVENING...LIKELY PIVOTING ESE. WITH AMDAR DATA INVOF KOMA
   DEPICTING SATURATION DOWN TO ABOUT 850 MB /COMPARED TO 700 MB IN THE
   12Z RAOB/...THE I-80 CORRIDOR IN IA SHOULD BE ROUGHLY THE SRN EXTENT
   OF HEAVY SNOW THROUGH 02Z.

   ..GRAMS.. 11/20/2015


   ATTN...WFO...DVN...ARX...DMX...FSD...OAX...

   LAT...LON   41369454 41309291 41449185 41729126 42089103 42549109
               43089231 43329451 43139606 42749678 42199704 41829663
               41699615 41369454