Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1259
The Storm Prediction Center issued this mesoscale discussion at Jul 11, 2021, 5:41 PM EDT for 18 counties in Pennsylvania. It was in force for 94 min.
The area
The outline as issued.
The facts
- Issued
- Jul 11, 2021, 5:41 PM EDT (21:41 UTC)
- Expired
- Jul 11, 2021, 7:15 PM EDT
- In force
- 94 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 372
Counties Bedford County, PA, Blair County, PA, Cambria County, PA, Centre County, PA, Clearfield County, PA, Clinton County, PA, Huntingdon County, PA, Indiana County, PA, Juniata County, PA, Lycoming County, PA, Mifflin County, PA, Montour County, PA, Northumberland County, PA, Perry County, PA, Snyder County, PA, Somerset County, PA, Sullivan County, PA, Union County, PA
The radar
The State College radar (KCCX), 33 km from the middle of the area, began a volume at 21:45 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, 9.7 hours before the alert went out and 172 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
- 5 J/kg
- Mixed-layer CIN
- -180 J/kg
- Mixed-layer LCL
- 979 m above ground
- 0-6 km bulk shear
- 36 kt
- 0-1 km storm-relative helicity
- 90 m²/s²
- 0-3 km storm-relative helicity
- 135 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
020
ACUS11 KWNS 112141
SWOMCD
SPC MCD 112141
PAZ000-MDZ000-112315-
Mesoscale Discussion 1259
NWS Storm Prediction Center Norman OK
0441 PM CDT Sun Jul 11 2021
Areas affected...Central Pennsylvania
Concerning...Severe Thunderstorm Watch 372...
Valid 112141Z - 112315Z
The severe weather threat for Severe Thunderstorm Watch 372
continues.
SUMMARY...Damaging winds remain the primary threat in central
Pennsylvania. A conditional tornado threat also exists with storms
that favorably interact with the warm front.
DISCUSSION...A few thunderstorms within the broken line along the
western edge of the Allegheny Mountains have exhibited some
supercell structure. A few isolated cells have also developed within
the warm sector in central Pennsylvania. While the primary threat
with these storms will likely remain damaging wind gusts, there
remains a conditional threat for a tornado with storms that interact
with the warm front. The KCCX VWP shows over 200 m2/s2 0-1 km SRH.
The greatest tornado potential would exist with the discrete storms
prior to them crossing the cold front or being overtaken by the
broken line to the west. With water vapor imagery showing shortwave
ridging in the area, there is uncertainty as to how much the
discrete, warm sector storms will become. If they do mature, the
process will be relatively slow given poor lapse rates aloft.
..Wendt.. 07/11/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BGM...CTP...LWX...PBZ...
LAT...LON 39837963 40547931 41217857 41527757 41567650 41417640
40657677 40107758 39687894 39837963SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 11, 2:05 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Bedford, Blair, Butler and 15 more | 55 min |
| Jul 11, 2:40 PM EDT | Severe Thunderstorm Watch | SPC | Adams, Allegheny, Armstrong, Beaver, Bedford, Blair and 39 more | 8 hr |
Nearby
Mesoscale Discussions in Pennsylvania, 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.