Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1263
The Storm Prediction Center issued this mesoscale discussion at Jul 11, 2021, 8:58 PM EDT for Carroll County, Washington County, Maryland; 17 counties in Pennsylvania. It was in force for 62 min.
The area
The outline as issued.
The facts
- Issued
- Jul 11, 2021, 8:58 PM EDT (00:58 UTC)
- Expired
- Jul 11, 2021, 10:00 PM EDT
- In force
- 62 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 372
Counties Carroll County, MD, Washington County, MD, Adams County, PA, Berks County, PA, Carbon County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Montour County, PA, Northumberland County, PA, Perry County, PA, Schuylkill County, PA, Snyder County, PA, York County, PA
The radar
The State College radar (KCCX), 133 km from the middle of the area, began a volume at 01:00 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
Washington/Dulle, VA (KIAD), launched 00:00Z, 1.0 hours before the alert went out and 149 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
- 811 J/kg
- Mixed-layer CIN
- -23 J/kg
- Mixed-layer LCL
- 1342 m above ground
- 0-6 km bulk shear
- 17 kt
- 0-1 km storm-relative helicity
- 25 m²/s²
- 0-3 km storm-relative helicity
- 57 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
709
ACUS11 KWNS 120059
SWOMCD
SPC MCD 120058
PAZ000-MDZ000-WVZ000-120200-
Mesoscale Discussion 1263
NWS Storm Prediction Center Norman OK
0758 PM CDT Sun Jul 11 2021
Areas affected...Eastern Pennsylvania...far northern Maryland
Concerning...Severe Thunderstorm Watch 372...
Valid 120058Z - 120200Z
The severe weather threat for Severe Thunderstorm Watch 372
continues.
SUMMARY...A threat for damaging winds will continue for another 1-2
hours. With time, though, the threat is expected to become more
marginal and isolated. No downstream watch is planned this evening.
DISCUSSION...A line of thunderstorms producing occasional wind
damage in central Pennsylvania will continue eastward this evening.
As temperatures cool ahead of the line and the influence of the MCV
to the north lessens, storms are likely to undergo a weakening trend
over the next couple of hours. In the short term, a small bookend
vortex near Columbia County, PA, will pose the greatest wind gusts
threat. This feature is near instability gradient and will be moving
into cooler, more stable air within the next 1-2 hours. A remaining
pocket of 1000-2000 J/kg MLCAPE in east-central Pennsylvania into
far northern Maryland may promote a few damaging gusts through 10-11
PM EDT. The southward extent of the threat is most is question as
low/mid-level forcing is weaker. Given the small spatial and
temporal extent of an increasingly marginal severe threat, no
downstream watch is planned this evening.
..Wendt.. 07/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...BGM...CTP...LWX...
LAT...LON 41077696 41127601 40947560 40707533 40187558 39787597
39557643 39517701 39507760 39547820 39667825 39907795
41077696SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 12, 1:32 PM EDT | Mesoscale Discussion | SPC | Allegany, Anne Arundel, Baltimore, Calvert, Caroline, Carroll and 12 more | 88 min |
| Jul 12, 3:34 PM EDT | Severe Thunderstorm Watch | SPC | Baltimore, Carroll, Cecil, Frederick, Harford, Howard and 2 more | 5 hr |
| Jul 12, 7:25 PM EDT | Mesoscale Discussion | SPC | Cecil, Harford, Kent | 2 hr |
Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in Maryland, 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.