Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1778
The Storm Prediction Center issued this mesoscale discussion at Sep 22, 2021, 6:13 PM EDT for Chautauqua County, New York; 11 counties in Pennsylvania. It was in force for 92 min.
The area
The outline as issued.
The facts
- Issued
- Sep 22, 2021, 6:13 PM EDT (22:13 UTC)
- Expired
- Sep 22, 2021, 7:45 PM EDT
- In force
- 92 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 510
Counties Chautauqua County, NY, Armstrong County, PA, Butler County, PA, Clarion County, PA, Crawford County, PA, Erie County, PA, Forest County, PA, Indiana County, PA, Jefferson County, PA, Venango County, PA, Warren County, PA, Westmoreland County, PA
The radar
The Pittsburgh radar (KPBZ), 79 km from the middle of the area, began a volume at 22:12 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
Pittsburgh, PA (KPIT), launched 12:00Z, 10.2 hours before the alert went out and 85 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.
- Mixed-layer CAPE
- 155 J/kg
- Mixed-layer CIN
- -120 J/kg
- Mixed-layer LCL
- 634 m above ground
- 0-6 km bulk shear
- 36 kt
- 0-1 km storm-relative helicity
- 32 m²/s²
- 0-3 km storm-relative helicity
- 88 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.5
The text
As transmitted.
494
ACUS11 KWNS 222214
SWOMCD
SPC MCD 222213
PAZ000-NYZ000-OHZ000-222345-
Mesoscale Discussion 1778
NWS Storm Prediction Center Norman OK
0513 PM CDT Wed Sep 22 2021
Areas affected...Western PA...Extreme Western NY
Concerning...Tornado Watch 510...
Valid 222213Z - 222345Z
The severe weather threat for Tornado Watch 510 continues.
SUMMARY...Severe threat is advancing downstream across western PA
into extreme western NY. Primary threat for damaging winds, along
with a tornado to two, will be over the next 1-2 hours.
DISCUSSION...Well-defined squall line has evolved over western PA
ahead of a strong short-wave trough that is ejecting across the OH
Valley. Partial heating has contributed to a narrow corridor of
instability that currently extends across western PA. Squall line
will surge past this buoyancy axis over the next 1-2 hours and
should begin to entrain cooler air which should lead to gradual
weakening. However, latest radar imagery depicts a well-defined MCV
over southeast Mercer County PA, lifting north-northeast toward the
western counties of NY. Embedded circulations are noted along the
squall line, immediately ahead of this feature. There is some
concern this activity could remain severe for the next 50-70 miles
which would be just beyond the edge of the current watch. Given the
poor air mass downstream, and the limited area where severe appears
possible, current thinking is a new watch may not be warranted.
..Darrow.. 09/22/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BUF...CTP...PBZ...CLE...
LAT...LON 39817947 40847986 41808064 42488006 42277902 40517873
39817947SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 22, 1:08 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Crawford and 8 more | 3 hr |
| Sep 22, 2:23 PM EDT | Tornado Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Crawford and 11 more | 6 hr |
| Sep 22, 4:08 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Crawford and 10 more | 97 min |
Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in New York, 2021Every 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.