Mesoscale Discussion 2056

Issued

Dec 25, 2021, 5:44 AM EST (10:44 UTC)

Expired

Dec 25, 2021, 10:45 AM EST

In force

5 hr

Issued by

the Storm Prediction Center

Concerning

Winter mixed precipitation

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399 
ACUS11 KWNS 251044
SWOMCD
SPC MCD 251044 
MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-251545-

Mesoscale Discussion 2056
NWS Storm Prediction Center Norman OK
0444 AM CST Sat Dec 25 2021

Areas affected...portions of northeastern and extreme eastern
NY...VT...central/southern NH...extreme southwestern ME...MA except
southeastern areas...northern parts of CT/RI.

Concerning...Winter mixed precipitation 

Valid 251044Z - 251545Z

SUMMARY...A mix of winter precip will pass over northeastern NY and
much of central/western New England through the remainder of the
morning.  This mostly will involve a transition from light snow to
freezing rain to rain.  Freezing rain rates of 0.05 to 0.15
inches/hour are possible for 2-3 hours in some locales, before the
precip transitions to all rain.

DISCUSSION...Moisture-channel imagery indicates a shortwave trough
moving rapidly east-northeastward across the IL/IN area and lower
Ohio Valley, ahead of which a broad low-level warm-advection and
moisture-transport plume extends across much of the Northeast.  This
corresponds to the northern branch of a two-pronged LLJ in the
eastern CONUS, with that northern branch extending across PA and
over parts of New England, per regional VWP data.  An area of precip
that has developed in the regime of large-scale lift will shift
eastward to east-northeastward across the discussion area before the
boundary layer warms above 32 F.  Expect mainly light (locally/
briefly heavier) and patchy snow on the leading edges, transitioning
to freezing rain within roughly 1-2 hours, then rain 2-3 hours
later.  

The bulk of hazardous winter precip should fall as freezing rain,
with time series of forecast soundings reasonably showing a
supportive superfreezing warm nose developing above the shallow/
near-surface subfreezing layer.  This process already is evident
across much of eastern NY, with light freezing rain reported at
several stations.  The thickening warm layer will melt progressively
greater snow amounts generated in a much-higher, essentially
saturated dendritic-growth layer (centered between 500-550 mb), with
saturated conditions extending to the surface a couple hours before
freezing-rain/rain transition is complete.  Continued warm advection
will extend into the boundary layer with time, and from west to
east, through mid/late morning.  As this occurs, surface and
near-surface temperatures will exceed 32 F, ending the freezing-rain
episode.

..Edwards.. 12/25/2021

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

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

LAT...LON   44997238 44557209 44167145 43557070 43127056 42917082
            42717075 42707068 42717059 42647059 42597071 42547084
            42407096 42327096 42297087 42277075 42007063 41997067
            41967051 41787175 42227334 43087366 43887465 44617446
            44987411 44997238

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.