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Mesoscale Discussion 72
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   Mesoscale Discussion 0072
   NWS Storm Prediction Center Norman OK
   0616 PM CST Wed Jan 18 2017

   Areas affected...Portions of the Sierra Nevada in central/northern

   Concerning...Heavy snow 

   Valid 190016Z - 190515Z

   SUMMARY...Heavy snowfall (generally above 3500-4500 ft) will
   continue and develop southward across the northern/central Sierra
   Nevada this evening into tonight. Snowfall rates upwards of 2+
   inches per hour will be possible across higher elevations.

   DISCUSSION...An expansive area of precipitation exists across much
   of central/northern California late this afternoon, in response to a
   mid-level jet streak progressing southeast along the CA coast and a
   related plume of enhanced tropospheric moisture (e.g., PW values
   near 1 inch). Near-term guidance and regional radar data depict
   increasing southwesterly 700-mb flow approaching portions of the
   western Sierra slopes, which will enhance upslope flow and
   precipitation rates. Heavier rates will expand down the Sierra range
   as this stronger flow evolves southward this evening into the
   overnight. Moreover, KBBX velocity data illustrate strong veering
   with height, indicating ample warm-air advection which is also
   contributing to higher rates. Recent KDAX data show pockets of
   higher specific differential phase (KDP) around 15000 ft, likely
   suggesting efficient crystal growth supporting higher snowfall rates
   (upwards of 1-2+ inches per hour) at higher elevations. Strong wind
   gusts will also combine with this snowfall to occasionally restrict
   visibility across higher passes.

   KBBX correlation coefficient (CC) data indicate snow levels
   currently around 3500-4000 ft across parts of the northern Sierra
   range, while KDAX CC data indicate these levels rising to around
   5000-6000 ft farther south. These levels will fluctuate slightly
   through the evening (with diabatic effects in heavier bands
   periodically lowering levels) before they more consistently descend
   overnight with the arrival of mid-level cooling.

   ..Picca.. 01/19/2017


   LAT...LON   36511883 38502036 38782043 39422090 39942150 40322170
               40552136 40442101 39932036 37881917 36731841 36391840
               36211858 36511883 

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