SPC MD 131

MD 0131 CONCERNING WINTER MIXED PRECIPITATION FOR PORTIONS OF WESTERN NEW ENGLAND...CENTRAL AND EASTERN NY...FAR NORTHEAST PA

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
overnight. 

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

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...GYX...BOX...BTV...ALY...BGM...

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

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