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Mesoscale Discussion 140
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   Mesoscale Discussion 0140
   NWS Storm Prediction Center Norman OK
   1024 PM CST Sun Feb 05 2017

   Areas affected...Portions of the Sierra of northern and central CA

   Concerning...Heavy snow 

   Valid 060424Z - 061030Z

   SUMMARY...Snowfall rates are expected to increase to near 2 inches
   per hour across portions of the Sierra around the 05Z-08Z time
   frame, affecting elevations generally above 6000-6500 feet.

   DISCUSSION...The latest water vapor loop indicates a midlevel
   shortwave trough approaching the coast of northern and central CA.
   Ascent accompanying the exit region of a speed maximum attendant to
   the trough, coupled with ample upslope flow resulting from
   Sierra-range orthogonal low/midlevel flow, will continue to support
   an increase in precipitation rates into the overnight hours. The
   overlap of abundant ascent with sufficiently deep and saturated
   dendritic growth zones, will support near-2-inch/hour snowfall 
   rates -- aided by the influx of Pacific moisture (PW around 0.7-0.9
   inch). Present indications are that the initiation of these rates
   will most likely occur around 05Z-08Z, based upon the current motion
   of an area of precipitation accompanying the aforementioned
   large-scale ascent and the latest short-range model guidance. Such
   rates will be most likely for elevations above 6000-6500 feet, and
   may continue well into the overnight hours -- and perhaps into
   Monday morning particularly with southward extent across the area.

   ..Cohen.. 02/06/2017


   LAT...LON   36941898 37881960 38972034 39372051 39572051 39542033
               39021995 38611967 38141931 37541883 36941841 36531832
               36341841 36941898 

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