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Mesoscale Discussion 29
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   MESOSCALE DISCUSSION 0029
   NWS STORM PREDICTION CENTER NORMAN OK
   0821 PM CST TUE JAN 19 2016

   AREAS AFFECTED...CNTRL/SRN IL AND ADJACENT PORTIONS OF SE MO...WRN
   KY...W CNTRL/SW IND

   CONCERNING...HEAVY SNOW 

   VALID 200221Z - 200515Z

   SUMMARY...SNOW...INCLUDING AT LEAST A COUPLE HOUR PERIOD OF HEAVY
   SNOW RATES IN EXCESS OF 1 INCH PER HOUR...WILL OVERSPREAD MUCH OF
   CENTRAL AND SOUTHERN ILLINOIS AND PORTIONS OF ADJACENT STATES
   THROUGH 03-06Z...BEFORE DIMINISHING.  HEAVIEST SNOW RATES MAY IMPACT
   THE I-64 CORRIDOR NEAR MT. VERNON IL THROUGH THE EVANSVILLE IND
   AREA.

   DISCUSSION...AN AREA OF DEVELOPING SNOW ACROSS THE MIDDLE
   MISSISSIPPI VALLEY APPEARS LARGELY IN RESPONSE TO FORCING ASSOCIATED
   WITH LOW-LEVEL WARM ADVECTION...IN ADVANCE OF A COUPLE OF SHORT WAVE
   TROUGHS PROGRESSING INTO/THROUGH THE MISSISSIPPI VALLEY.  AS A
   SOUTHWESTERLY 850 MB SPEED MAXIMUM STRENGTHENS EAST OF THE I-44
   CORRIDOR OF SOUTH CENTRAL MISSOURI...TOWARD SOUTHERN ILLINOIS...
   HOURLY SNOW RATES APPEAR TO BE INCREASING SOUTH THROUGH EAST OF THE
   GREATER ST. LOUIS METROPOLITAN AREA.  SNOW RATES MAY INTENSIFY
   FURTHER THROUGH THE 03-06Z TIME FRAME...WITH INCREASING LARGE-SCALE
   ASCENT AND LOW-LEVEL MOISTURE RETURN ACROSS AND SOUTH OF THE I-64
   CORRIDOR OF SOUTHERN ILLINOIS INTO SOUTHERN INDIANA.

   ANOTHER RELATIVE MAXIMUM IN SNOWFALL RATES APPEARS TO BE DEVELOPING
   ALONG A LOWER/MID TROPOSPHERIC THERMAL GRADIENT ACROSS THE
   SPRINGFIELD/DECATUR IL AREA TOWARD TERRE HAUTE IN.  THIS MAY PERSIST
   AND INTENSIFY FURTHER THROUGH LATE EVENING...BEFORE DIMINISHING
   AFTER 06Z AS LARGE-SCALE ASCENT SHIFTS EASTWARD INTO THE OHIO VALLEY
   AND WEAKENS.

   GIVEN THE RELATIVELY HIGH SNOW TO LIQUID WATER RATIOS ASSOCIATED
   WITH THE COLD LOW-LEVEL ENVIRONMENT...AND THE PLUME OF PRECIPITABLE
   WATER ON THE ORDER OF ONE-HALF INCH OVERSPREADING THE REGION...LIFT
   APPEARS SUFFICIENT TO SUPPORT AT LEAST A COUPLE HOUR PERIOD OF SNOW
   RATES IN EXCESS OF 1 INCH PER HOUR.

   ..KERR.. 01/20/2016


   ATTN...WFO...LMK...IND...PAH...ILX...LSX...

   LAT...LON   38398991 39059054 39749073 40278867 39998724 39238627
               38208643 37618751 37158893 37269027 38149000 38398991 

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Page last modified: January 20, 2016
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