MESOSCALE DISCUSSION 0113
   NWS STORM PREDICTION CENTER NORMAN OK
   0917 AM CST SUN FEB 20 2011
   
   AREAS AFFECTED...MUCH OF SD AND FAR SOUTHERN ND TO SOUTH-CENTRAL MN
   
   CONCERNING...HEAVY SNOW 
   
   VALID 201517Z - 201945Z
   
   HEAVY SNOWFALL WILL CONTINUE TO DEVELOP/INTENSIFY IN A GENERAL
   WEST-EAST CORRIDOR ACROSS SD /MAINLY NORTH OF I-90/ AND EXTREME
   SOUTHERN ND INTO SOUTH-CENTRAL MN INCLUDING THE TWIN CITIES.
   LOCALIZED SNOWFALL RATES OF 1-2 IN/HR ARE LIKELY...ALONG WITH
   BLIZZARD CONDITIONS AT TIMES ESPECIALLY ACROSS PORTIONS OF EASTERN
   SD/SOUTHEAST ND AND SOUTHWEST MN.
   
   AS A LEAD SHORTWAVE TROUGH CONTINUES TO PIVOT NORTHEASTWARD OVER THE
   NORTHERN HIGH PLAINS...CONSIDERABLE DEEP FORCING FOR ASCENT OWING TO
   DPVA...A COUPLED JET ALOFT...AND STRONG LOW LEVEL WARM
   ADVECTION/ISENTROPIC LIFT WILL CONTRIBUTE TO A FAVORABLE SCENARIO
   FOR HEAVY SNOWFALL WITH AN ARCTIC AIRMASS IN PLACE ACROSS THE
   REGION. WITH SLANTWISE/SOME UPRIGHT CAPE AS EVIDENCED BY ONGOING
   LIGHTNING THIS MORNING ACROSS FAR SOUTHERN MN/MUCH OF IA...AND STEEP
   LAPSE RATES/WEAK ELEVATED BUOYANCY NOTED IN UPSTREAM OBSERVED RAOBS
   SUCH AS 12Z RAPID CITY/NORTH PLATTE...PROXIMITY OF WEAK STATIC
   STABILITY/STEEPENING LAPSE RATES ALOFT WILL CONTRIBUTE TO ENHANCED
   SNOWFALL RATES WITH OTHERWISE FAVORABLE THERMODYNAMIC PROFILES FOR
   AMPLE DENDRITIC/AGGREGATE SNOW GROWTH PER 12Z NAM/RUC FORECAST
   SOUNDINGS. IN ADDITION...STRONG NORTHEASTERLY WINDS WILL CONTRIBUTE
   TO BLIZZARD CONDITIONS AT TIMES...ESPECIALLY ACROSS EASTERN
   SD/SOUTHEAST ND/SOUTHWEST MN TO THE EAST/NORTHEAST OF A DEVELOPING
   INVERTED SURFACE TROUGH.
   
   ..GUYER.. 02/20/2011
   
   
   ATTN...WFO...MPX...FGF...FSD...ABR...BIS...UNR...
   
   LAT...LON   45440348 46180202 46489752 46009324 45059293 44419385
               44339762 43510071 44120282 45440348