Alert archive / Pennsylvania / Mesoscale Discussions in 2021

Mesoscale Discussion 1738

September 13, 2021Allegany County, Cattaraugus County, Chautauqua County, New York; 8 counties in Pennsylvania

The Storm Prediction Center issued this mesoscale discussion at Sep 13, 2021, 4:11 PM EDT for Allegany County, Cattaraugus County, Chautauqua County, New York; 8 counties in Pennsylvania. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 13, 2021, 4:11 PM EDT (20:11 UTC)
Expired: Sep 13, 2021, 6:15 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Allegany County, NY, Cattaraugus County, NY, Chautauqua County, NY, Cameron County, PA, Clinton County, PA, Elk County, PA, Erie County, PA, Forest County, PA, McKean County, PA, Potter County, PA, Warren County, PA

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 496Sep 13, 5:50 PM EDT

The nearest sounding before it

Buffalo Intl Airport, NY (KBUF), launched 12:00Z, 8.2 hours before the alert went out and 114 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: 1305 m above ground
0-6 km bulk shear: 57 kt
0-1 km storm-relative helicity: -1 m²/s²
0-3 km storm-relative helicity: 154 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

349 
ACUS11 KWNS 132011
SWOMCD
SPC MCD 132011 
PAZ000-NYZ000-OHZ000-132215-

Mesoscale Discussion 1738
NWS Storm Prediction Center Norman OK
0311 PM CDT Mon Sep 13 2021

Areas affected...western New York/northwestern Pennsylvania

Concerning...Severe potential...Watch unlikely 

Valid 132011Z - 132215Z

Probability of Watch Issuance...20 percent

SUMMARY...A cluster of storms crossing Lake Erie may pose risk for
locally strong/gusty winds.  While severe risk appears limited, and
thus WW not anticipated in the near term, we will continue to
monitor environmental/convective evolution.

DISCUSSION...Latest radar loop shows a loosely organized cluster of
thunderstorms that continues moving east-southeastward, now crossing
Lake Erie.  The storms have remained just north of the surface
front, slightly elevated atop a stable boundary layer.  However, as
the storms continue east-southeastward and move off the lake into
adjacent NY/PA, a more moist boundary layer suggests less stability
-- and perhaps risk that stronger gusts may occur locally.  While
potential for gusts in excess of 50 kt appears to remain low, and
thus need for a watch likely not required in the short term, we will
monitor for any changes in the environment, or in the character of
the convection, which might hint at greater wind risk, and
possible/associated need for WW consideration.

..Goss/Thompson.. 09/13/2021

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

ATTN...WFO...BGM...BUF...CTP...PBZ...CLE...

LAT...LON   42568025 42387823 41987712 41197766 41517953 42028107
            42278132 42568025

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 12, 9:14 PM EDT	Mesoscale Discussion	SPC	Erie	91 min
Sep 12, 10:25 PM EDT	Severe Thunderstorm Watch	SPC	Allegany, Cattaraugus, Chautauqua, Chemung, Erie, Genesee and 7 more	4 hr
Sep 13, 12:26 AM EDT	Mesoscale Discussion	SPC	Allegany, Broome, Chemung, Chenango, Cortland, Delaware and 9 more	94 min
Sep 13, 5:53 PM EDT	Severe Thunderstorm Watch	SPC	Cameron, Centre, Clarion, Clearfield, Clinton, Columbia and 14 more	3 hr
Sep 13, 7:07 PM EDT	Mesoscale Discussion	SPC	Carbon, Centre, Clearfield, Columbia, Jefferson, Luzerne and 5 more	113 min
Sep 13, 7:44 PM EDT	Severe Thunderstorm Watch	SPC	Bucks, Carbon, Lehigh, Luzerne, Monroe, Northampton	4 hr

Nearby

Mesoscale Discussions in Pennsylvania, 2021 Mesoscale Discussions in New York, 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.