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Mesoscale Discussion 1929
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   MESOSCALE DISCUSSION 1929
   NWS STORM PREDICTION CENTER NORMAN OK
   1252 PM CST THU NOV 20 2014

   AREAS AFFECTED...AREAS OF NEW YORK NEAR AND SOUTH OF BUFFALO
   INCLUDING PORTIONS OF THE WESTERN SOUTHERN TIER

   CONCERNING...HEAVY SNOW 

   VALID 201852Z - 202345Z

   SUMMARY...AN INTENSE LAKE-EFFECT SNOW BAND NEAR AND S OF THE BUFFALO
   AREA IS LIKELY PRODUCING SNOWFALL RATES OF 2-4 INCHES PER HOUR...AND
   WILL CONTINUE IN THE SHORT-TERM. OTHER AREAS FARTHER SOUTH INTO THE
   WESTERN SOUTHERN TIER WILL LIKELY EXPERIENCE HEAVY SNOW LATER THIS
   AFTERNOON INTO THE EVENING AS THE SNOW BAND EVOLVES.

   DISCUSSION...MOSAIC RADAR IMAGERY INDICATES A SOLITARY...HEAVY-SNOW
   BAND HAVING GRADUALLY EDGED NWD IN THE LEE OF LAKE ERIE. THIS
   EVOLUTION MAY BE IN RESPONSE TO SLIGHT BACKING OF FLOW BELOW 2 KM
   AGL SINCE 15Z...PER THE BUF VWP...PERHAPS RELATED TO AN ISALLOBARIC
   RESPONSE ACCOMPANYING MODEST SFC PRESSURE FALLS OVER THE ST LAWRENCE
   VALLEY.

   DURING THE NEXT FEW HOURS -- PERHAPS THROUGH 21Z OR 22Z -- THE SNOW
   BAND WILL LIKELY REMAIN IN A QUASI-STEADY-STATE CONFIGURATION FROM
   THE SRN TWO-THIRDS OF ERIE COUNTY INCLUDING THE SOUTH SUBURBS OF
   BUFFALO INTO WYOMING AND SRN GENESEE COUNTIES. KBUF SRM DATA
   INDICATE OCCASIONAL MESO-GAMMA-SCALE CIRCULATIONS EMBEDDED WITHIN
   THE SNOW BAND...WHICH MAY BE ACCOMPANIED BY SMALL-SCALE ENHANCEMENTS
   TO VERTICAL MOTION ALONG WITH THE HIGHEST SNOWFALL RATES -- PERHAPS
   REACHING 4 INCHES PER HOUR. OTHERWISE...SNOWFALL RATES OF 2-3 INCHES
   PER HOUR WILL BE COMMON WITH THE CORE OF THE SNOW BAND.
   ALSO...CONVECTIVE TURRETS EMBEDDED WITHIN THE SNOW BAND OVER
   MID-LAKE PER VIS IMAGERY CORRESPOND TO HIGHER REFLECTIVITY CORES PER
   MOSAIC RADAR IMAGERY. AN ISOLATED LIGHTNING STRIKE OR TWO MAY OCCUR
   OWING TO THE LAKE-ENHANCED CONVECTIVE BOUNDARY LAYER. SNOWFALL RATES
   TO 4 INCHES PER HOUR MAY ALSO OCCUR WITH THUNDERSTORMS.

   UPSTREAM OBSERVATIONS OVER LOWER MI INDICATE SFC WINDS VEERING...IN
   RESPONSE TO PRESSURE RISES ON THE SUBSIDENT/UPSTREAM SIDE OF A
   SUBTLE MID-LEVEL VORT MAX CROSSING THE GREAT LAKES. PRESENT
   INDICATIONS ARE THAT...IN THE 22-00Z TIME FRAME...THE BACKGROUND
   LOWER-TROPOSPHERIC FLOW WILL VEER INVOF THE INITIALLY SOLITARY SNOW
   BAND. THIS WILL LIKELY DISRUPT THE BAND...PERHAPS SHUNTING IT SWD
   TOWARD THE WRN SRN TIER INCLUDING PORTIONS OF CHAUTAUQUA AND
   CATTARAUGUS COUNTIES OR BREEDING A FRAGMENTATION OF THE BAND INTO
   MULTIPLE SHORTER SEGMENTS. ULTIMATELY...THE VEERING OF THE LOW-LEVEL
   FLOW WILL CORRESPOND TO A DECREASE IN OVER-LAKE FETCH LENGTH...WITH
   SNOWFALL RATES PROBABLY DECREASING BY EARLY EVENING.

   ..COHEN.. 11/20/2014


   ATTN...WFO...BUF...

   LAT...LON   42447932 42777898 42897858 42937818 42677822 42407893
               42447932 

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Page last modified: November 20, 2014
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