Mesoscale Discussion 65

Issued

Feb 7, 2021, 11:40 AM EST (16:40 UTC)

Expired

Feb 7, 2021, 3:45 PM EST

In force

4 hr

Issued by

the Storm Prediction Center

Concerning

Heavy snow

Counties Bristol County, MA, Norfolk County, MA, Plymouth County, MA, Suffolk County, NY, Bristol County, RI, Kent County, RI, Newport County, RI, Providence County, RI, Washington County, RI

The Brookhaven radar (KOKX), 86 km from the middle of the area, began a volume at 16:41 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

504 
ACUS11 KWNS 071641
SWOMCD
SPC MCD 071640 
MAZ000-RIZ000-CTZ000-NYZ000-072045-

Mesoscale Discussion 0065
NWS Storm Prediction Center Norman OK
1040 AM CST Sun Feb 07 2021

Areas affected...Long Island through southeastern New England

Concerning...Heavy snow 

Valid 071640Z - 072045Z

SUMMARY...Heavy snow is in the process of developing, with hourly
snow rates expected to maximize around to 2-3+ inches per hour by
2-4 PM EST across the Greater Providence and southern Greater Boston
Metropolitan areas.

DISCUSSION...Rapid deepening of a surface cyclone is now underway to
the east-northeast of the southern Mid Atlantic coast, as a 100 kt
cyclonic 500 mb jet streak, associated with a vigorous mid-level
short wave impulse, noses across the North Carolina coast.  This
system is forecast to accelerate northeastward through this
afternoon, with continued rapid deepening of the cyclone, and
intensifying deep-layer frontogenetic forcing to its
north-northeast.

Periods of heavy snow have already been observed within the
developing frontal precipitation band across parts of southeastern
Pennsylvania into the Greater New York City area, with increasing
snow rates in the process of developing across Long Island and
southern New England.  Latest model output suggests that forcing for
ascent will increasingly be aided by strengthening frontogenesis in
the 700-500 mb layer, across southeastern New England during the
18-21Z time frame.  

Forecast soundings indicate that this will include the favorably
cold mixed-phase layer supportive of large dendritic ice crystal
growth, which may maximize across Rhode Island and southeastern
Massachusetts.  This likely will include snow rates occasionally on
the order of 2 inches per hour, and at least some guidance appears
suggestive that an influx of lower/mid-level moisture may contribute
to weak destabilization supportive of convective bursts around 3+
inches per hour.

..Kerr.. 02/07/2021

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

ATTN...WFO...BOX...OKX...

LAT...LON   42057172 42467037 41767036 41227135 40827224 40497289
            40367332 40667359 41317278 42057172

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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.