Alert archive / New Jersey / Mesoscale Discussions in 2021

Mesoscale Discussion 118

February 18, 20215 states

The Storm Prediction Center issued this mesoscale discussion at Feb 18, 2021, 9:47 AM EST for 5 states. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Feb 18, 2021, 9:47 AM EST (14:47 UTC)
Expired: Feb 18, 2021, 1:45 PM EST
In force: 4 hr
Issued by: the Storm Prediction Center
Concerning: Heavy snow

All 45 counties

Bristol County, MA, Dukes County, MA, Nantucket County, MA, Bergen County, NJ, Burlington County, NJ, Camden County, NJ, Essex County, NJ, Gloucester County, NJ, Hudson County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Morris County, NJ, Ocean County, NJ, Passaic County, NJ, Somerset County, NJ, Sussex County, NJ, Union County, NJ, Warren County, NJ, Bronx County, NY, Kings County, NY, Nassau County, NY, New York County, NY, Putnam County, NY, Queens County, NY, Richmond County, NY, Rockland County, NY, Suffolk County, NY, Westchester County, NY, Berks County, PA, Bucks County, PA, Chester County, PA, Delaware County, PA, Lancaster County, PA, Lehigh County, PA, Montgomery County, PA, Northampton County, PA, Philadelphia County, PA, York County, PA, Bristol County, RI, Kent County, RI, Newport County, RI, Providence County, RI, Washington County, RI

The radar

The Brookhaven radar (KOKX), 50 km from the middle of the area, began a volume at 14:49 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.

The nearest sounding before it

Brookhaven, NY (KOKX), launched 12:00Z, 2.8 hours before the alert went out and 49 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1468 m above ground
0-6 km bulk shear: 82 kt
0-1 km storm-relative helicity: -2 m²/s²
0-3 km storm-relative helicity: 406 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

230 
ACUS11 KWNS 181447
SWOMCD
SPC MCD 181447 
MAZ000-RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-181845-

Mesoscale Discussion 0118
NWS Storm Prediction Center Norman OK
0847 AM CST Thu Feb 18 2021

Areas affected...Southeast Pennsylvania...New Jersey...southeast New
York...and portions of southern New England.

Concerning...Heavy snow 

Valid 181447Z - 181845Z

SUMMARY...Heavy snow is expected to continue through early afternoon
with snowfall rates up to 2 inches per hour possible.

DISCUSSION...An expansive precipitation associated with broad
isentropic ascent has overspread much of the mid-Atlantic and has
started to move into New England. Moderate snowfall rates are being
observed across much of the region with heavy snowfall currently
being observed in southeast Pennsylvania. This area of heavy
snowfall is expected to pivot northeastward through the morning and
early afternoon across New Jersey and eventually Long Island. The
current transition zone between snow and sleet/freezing rain is near
the Pennsylvania/Maryland border and across far southern New Jersey.
This transition zone is expected to lift northeastward through the
morning into southeast Pennsylvania, central New Jersey, and
possibly to Long Island bringing a mix of freezing rain and sleet to
these regions. Areas to the north of this transition zone are
expected to see the heaviest snowfall rates and likely the greatest
snowfall totals where precipitation type remains all snow.

..Bentley.. 02/18/2021

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

ATTN...WFO...BOX...OKX...ALY...PHI...BGM...CTP...LWX...

LAT...LON   40807573 41297446 41687340 41967256 42087155 41817053
            41617009 41316992 41177020 41207115 40987187 40537309
            40327378 39847401 39867415 39647482 39667577 39697691
            40227665 40627605 40807573

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Feb 18, 10:23 AM EST	Mesoscale Discussion	SPC	Cape May, Cumberland, Salem	3 hr

Nearby

Mesoscale Discussions in New Jersey, 2021 Mesoscale Discussions in New York, 2021 Mesoscale Discussions in Pennsylvania, 2021 Every mesoscale discussion in 2021

Sources

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.