Wednesday, February 25, 2015

Rare - Heavy Snow Rates of 1-2" per Hour

 The Storm Prediction Center (SPC)  in Oklahoma issues mesoscale discussions for heavy winter precipitation. Typically we see the above kind of weather highlight / discussion during possible tornado watches and other severe weather events. 

They issued this not too long ago - 8PM - talks about the heavy snow rates you are seeing outside your window now. One possibly 2+ inch snow rates per hour for a few hours. 

   MESOSCALE DISCUSSION 0100
   NWS STORM PREDICTION CENTER NORMAN OK
   0655 PM CST WED FEB 25 2015

   AREAS AFFECTED...PORTIONS OF NRN SC AND CNTRL NC

   CONCERNING...HEAVY SNOW 

   VALID 260055Z - 260700Z

   SUMMARY...A RAIN/SNOW MIX ACROSS NRN SC SHOULD TRANSITION TO ALL
   SNOW AND SHIFT NORTHEAST INTO CNTRL NC THROUGH 07Z. SNOWFALL RATES
   OF 1 IN/HR WILL BE LIKELY...WITH LOCALLY HIGHER RATES POSSIBLE.

   DISCUSSION...00Z SFC ANALYSIS INDICATES A LOW PRESSURE AREA OVER THE
   NRN GULF OF MEXICO...AND A WEAKENING AREA OF HIGH PRESSURE ACROSS
   ERN NC/VA. A SHORTWAVE TROUGH OVER THE LOWER MS RIVER VALLEY
   EMBEDDED WITHIN BROADER TROUGHING ACROSS THE ERN TWO-THIRDS OF THE
   CONUS WILL CONTINUE MOVING NEWD THROUGH THE OVERNIGHT HOURS. A BROAD
   AREA OF PRECIPITATION ASSOCIATED WITH THE SHORTWAVE TROUGH AND SFC
   LOW EXTENDS FROM MUCH OF THE DEEP SOUTH INTO NC/SC.

   OBSERVATIONS ACROSS NRN SC AS OF 00Z INDICATE NEAR-FREEZING SFC
   TEMPERATURES...AND RECENT NSSL MPING REPORTS INDICATE A RAIN/SNOW
   MIX IS BEGINNING TO TRANSITION TO ALL SNOW AS DYNAMIC COOLING OF THE
   LOW/MID-LEVELS CONTINUES. AS THIS PRECIPITATION MOVES NEWD INTO
   CNTRL NC WHERE SFC TEMPERATURES REMAIN ABOVE FREEZING...
   COOLING AND MOISTENING OF THE DRY SFC-700 MB LAYER EVIDENT IN THE
   00Z GSO SOUNDING WILL OCCUR. THIS WILL SUPPORT A TRANSITION FROM A
   RAIN/SNOW MIX TO ALL SNOW ACROSS CNTRL NC THROUGH 07Z. STRONG
   LOW-LEVEL WAA AND FRONTOGENETICAL FORCING WILL SUPPORT HEAVY SNOW
   WITH RATES OF 1 IN/HR LIKELY. BASED ON UPSTREAM OBSERVATIONS FROM
   NRN MS/AL/GA...AND SREF PROBABILITIES...LOCALLY HIGHER SNOWFALL
   RATES OF 2+ IN/HR WILL BE POSSIBLE.

   ..GLEASON.. 02/26/2015


   ATTN...WFO...RAH...RNK...CAE...GSP