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ACUS11 KWNS 181553
SWOMCD
SPC MCD 181552=20
MAZ000-CTZ000-NYZ000-181915-

Mesoscale Discussion 2046
NWS Storm Prediction Center Norman OK
0952 AM CST Sat Dec 18 2021

Areas affected...Parts of southern NY...northern CT...and southern
MA

Concerning...Winter mixed precipitation=20

Valid 181552Z - 181915Z

SUMMARY...A mix of freezing rain, sleet, and snow will continue to
spread east-northeastward across portions of southern NY, northern
CT, and southern MA this morning into the afternoon.

DISCUSSION...Latest water vapor imagery shows a shortwave trough
advancing eastward across parts of the upper MS Valley this morning,
with related large-scale ascent overspreading the northeastern
states. A shield of ongoing precipitation including a mix of
freezing rain, sleet, and snow is evident across portions of
northern PA, southern NY, and farther east into New England. Latest observations across the region show near-freezing surface
temperatures aided by modest surface cold advection beneath a northward-advancing plume of warm air advection aloft. This
isothermal structure (supported by NAM/RAP forecast soundings) will
continue to support partial to full melting of descending
hydrometers and associated sleet and freezing rain extending across
parts of southern NY into southern MA and northern CT. Farther north
across portions of central New York, deeper sub-freezing layers and
increasing ascent will support periods of moderate to heavy snow
with rates approaching 1 in/hr. The latest high-resolution ensemble
guidance suggests that a band of freezing rain extending across
southern NY into western MA and CT could be associated with rates of
0.05 in/hr (locally 0.1 in per/hr) later this morning into the
afternoon timeframe. A gradual transition to rain should occur from
south to north across the area this afternoon as increasing warm air
advection aloft overspreads most of the area (outside of higher
terrain).

..Weinman.. 12/18/2021

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!o-jHGd3-ibtN0VS4y_a3k7914eAUJ53gchr8kgYF1rQ1SusB1lnCYw0tYq_tquCQz5KnmmzF$=
for graphic product...

ATTN...WFO...BOX...OKX...ALY...BGM...BUF...

LAT...LON 42107690 42117781 42157843 42407880 42847868 43107851
43077750 43037663 42967598 42787522 42567424 42377328
42327263 42267218 42097186 41747188 41687219 41767347
41797383 41687423 41627472 41937502 42147562 42107690=20



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