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Mesoscale Discussion 131
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   Mesoscale Discussion 0131
   NWS Storm Prediction Center Norman OK
   0714 PM CST Mon Jan 23 2017

   Areas affected...Portions of western New England...central and
   eastern NY...far northeast PA

   Concerning...Winter mixed precipitation 

   Valid 240114Z - 240715Z

   SUMMARY...Areas of winter mixed precipitation will spread northward
   through the evening hours, and continue overnight.

   DISCUSSION...Ascent accompanying the warm conveyor and deformation
   zone of deep cyclone advancing northward from the Mid Atlantic
   region, will support the northward spread of winter mixed
   precipitation across parts of the Northeast. This will occur during
   the next few hours of the evening, with this activity continuing

   Conventional observations, and New York State Mesonet observations,
   suggest that sub-freezing surface temperatures/wet-bulb surface
   temperatures will affect areas from far northeast PA arching
   northeastward and east-northeastward through portions of the Hudson
   Valley and into the vicinity of western MA and southern VT/NH.
   Modest surface cold advection, and evaporative cooling within the
   sub-cloud layer, will maintain these sub-freezing temperatures
   through the night. Upon comparisons to surface observations, RAP/NAM
   soundings -- especially those farther south -- have exhibited warm
   biases in some areas. Thus, the Mesoscale Discussion area has been
   confined to locations where confidence is greatest in sub-freezing
   surface temperatures persisting through the night, with substantial
   deference to observational trends.

   Given the sub-freezing surface temperatures, areas of freezing rain,
   sleet, and snow will affect the area. Snow -- with rates potentially
   locally reaching 0.5-1.0 inch per hour -- would be most likely
   across western areas of central NY. However, elevated dendritic
   growth zones -- relative to the strongest ascent in the profile --
   cast some degree of doubt regarding the potential for sustained
   episodes of snow growth across the region -- especially with
   eastward extent.

   Furthermore, highly variable precipitation types with small
   displacements across the region may occur, attributable to (1)
   terrain heterogeneity and its influence on the spatial pattern of
   the low-level thermal profile, and (2) the marginality of
   above-freezing temperatures in the elevated warm layer sampled by
   the 00Z Albany sounding. In cases of descending liquid hydrometeors
   that freeze/re-freeze within the boundary layer, pockets of sleet
   and freezing rain will be possible across the area. Freezing-rain
   rates around 0.02-0.04 inch per hour will be possible, with
   sleet-accumulation rates locally reaching around 0.05-0.10 inch per
   hour. The risk for winter mixed precipitation will continue into the
   overnight hours.

   ..Cohen.. 01/24/2017


   LAT...LON   43487401 43347261 42637221 42257371 41757546 41977623
               42687606 43267513 43487401 

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