Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1777
The Storm Prediction Center issued this mesoscale discussion at Sep 22, 2021, 4:08 PM EDT for 6 counties in Ohio; 16 counties in Pennsylvania; 4 counties in West Virginia. It was in force for 97 min.
The area
The outline as issued.
The facts
- Issued
- Sep 22, 2021, 4:08 PM EDT (20:08 UTC)
- Expired
- Sep 22, 2021, 5:45 PM EDT
- In force
- 97 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 510
All 26 counties
Ashtabula County, OH, Carroll County, OH, Columbiana County, OH, Jefferson County, OH, Mahoning County, OH, Trumbull County, OH, Allegheny County, PA, Armstrong County, PA, Beaver County, PA, Butler County, PA, Clarion County, PA, Crawford County, PA, Erie County, PA, Fayette County, PA, Forest County, PA, Greene County, PA, Jefferson County, PA, Lawrence County, PA, Mercer County, PA, Venango County, PA, Washington County, PA, Westmoreland County, PA, Brooke County, WV, Hancock County, WV, Monongalia County, WV, Ohio County, WV
The radar
The Pittsburgh radar (KPBZ), 13 km from the middle of the area, began a volume at 20:07 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, 8.1 hours before the alert went out and 26 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.
383
ACUS11 KWNS 222009
SWOMCD
SPC MCD 222008
PAZ000-WVZ000-OHZ000-222145-
Mesoscale Discussion 1777
NWS Storm Prediction Center Norman OK
0308 PM CDT Wed Sep 22 2021
Areas affected...Portions of eastern OH...western PA...and northern
WV
Concerning...Tornado Watch 510...
Valid 222008Z - 222145Z
The severe weather threat for Tornado Watch 510 continues.
SUMMARY...Scattered damaging winds and a couple of tornadoes will
remain possible through the rest of the afternoon.
DISCUSSION...A broken line of storms has formed this afternoon
across eastern OH and northern WV along and just ahead of a cold
front. The environment downstream of this convection into western PA
will remain favorable for organized severe storms, with MLCAPE of
500-1000 J/kg and around 40-50 kt of deep-layer shear present per
latest mesoanalysis estimates. Scattered damaging winds will
probably be the main threat with these mostly linear storms as they
move generally northeastward through the rest of the afternoon.
There still remains a chance for a couple tornadoes, as 0-1 km SRH
around 150 m2/s2 is present based on recent VWPs from KPBZ and
surface winds remain backed to southeasterly across western PA.
These tornadoes may occur either with low-topped cells that have
recently developed ahead of the broken line, or with circulations
embedded within the line itself.
..Gleason.. 09/22/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...PBZ...CLE...
LAT...LON 39528042 39988055 40158091 40818128 41288108 41888105
42197999 41207890 39747948 39508000 39528042SPC 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 | Ashtabula, Belmont, Carroll, Columbiana, Geauga, Guernsey and 11 more | 3 hr |
| Sep 22, 2:23 PM EDT | Tornado Watch | SPC | Ashtabula, Belmont, Carroll, Columbiana, Geauga, Harrison and 7 more | 6 hr |
| Sep 22, 6:13 PM EDT | Mesoscale Discussion | SPC | Armstrong, Butler, Clarion, Crawford, Erie, Forest and 5 more | 92 min |
| Sep 22, 2:44 PM EDT | Mesoscale Discussion | SPC | Monroe | 3 hr |
Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in Ohio, 2021Mesoscale Discussions in West Virginia, 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.