Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 951
The Storm Prediction Center issued this mesoscale discussion at Jun 13, 2021, 2:38 PM EDT for 26 counties in Pennsylvania. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Jun 13, 2021, 2:38 PM EDT (18:38 UTC)
- Expired
- Jun 13, 2021, 4:45 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 26 counties
Blair County, PA, Bradford County, PA, Cambria County, PA, Cameron County, PA, Centre County, PA, Clearfield County, PA, Clinton County, PA, Columbia County, PA, Elk County, PA, Huntingdon County, PA, Juniata County, PA, Lackawanna County, PA, Luzerne County, PA, Lycoming County, PA, Mifflin County, PA, Montour County, PA, Northumberland County, PA, Perry County, PA, Potter County, PA, Schuylkill County, PA, Snyder County, PA, Sullivan County, PA, Susquehanna County, PA, Tioga County, PA, Union County, PA, Wyoming County, PA
The radar
The State College radar (KCCX), 60 km from the middle of the area, began a volume at 18:40 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 6.6 hours before the alert went out and 235 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 664 m above ground
- 0-6 km bulk shear
- 30 kt
- 0-1 km storm-relative helicity
- 54 m²/s²
- 0-3 km storm-relative helicity
- 56 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
613
ACUS11 KWNS 131839
SWOMCD
SPC MCD 131838
PAZ000-132045-
Mesoscale Discussion 0951
NWS Storm Prediction Center Norman OK
0138 PM CDT Sun Jun 13 2021
Areas affected...portions of northern into central Pennsylvania
Concerning...Severe potential...Watch possible
Valid 131838Z - 132045Z
Probability of Watch Issuance...40 percent
SUMMARY...The severe threat appears to be increasing across portions
of northern into central Pennsylvania this afternoon. Damaging gusts
will be the primary threat, although a severe hailstone cannot be
ruled out. A Severe Thunderstorm Watch issuance is possible over the
next few hours.
DISCUSSION...In the wake of a passing MCS with associated cloud
cover, clearing skies and surface heating/boundary-layer mixing has
been underway for the past couple of hours ahead of a
southeast-sagging cold front. Isolated thunderstorm development is
also occurring ahead of the front given the surface heating and the
approach of a 700 mb impulse, with an increase in coverage expected
with time. Temperatures are warming well into the 70s F, with mid to
upper 60s F dewpoints evident via the latest METAR observations.
Low-level lapse rates are steepening into the 6.5-8 C/km range per
18Z mesoanalysis, contributing up to 1000 J/kg MLCAPE. While not
overly strong, mid to upper flow is stronger compared to points
farther west/southwest. Gradual veering in the surface-700 mb layer,
with an appreciable speed increase in the 700-500 mb layer is
resulting in up to 40 kts of effective bulk shear per 18Z
mesoanalysis and 17Z RAP forecast soundings.
Given the aforementioned kinematic/thermodynamic environment, at
least isolated strong to potentially severe wind-producing
multicellular storms are expected, and a transient supercell (with
potential for damaging gusts and perhaps a severe hailstone) is also
possible. Conditions are being monitored for the need of a Severe
Thunderstorm Watch.
..Squitieri/Grams.. 06/13/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...BGM...CTP...PBZ...
LAT...LON 41497897 41857839 41897716 41887551 41847534 41317538
40787601 40457667 40227745 40147798 40177842 40317887
41497897SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jun 13, 12:13 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Bedford, Butler, Cambria and 8 more | 2 hr |
| Jun 13, 12:50 PM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 9 more | 7 hr |
| Jun 13, 3:26 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 10 more | 94 min |
| Jun 13, 3:26 PM EDT | Severe Thunderstorm Watch | SPC | Blair, Bradford, Cambria, Cameron, Centre, Clearfield and 20 more | 7 hr |
| Jun 13, 4:56 PM EDT | Mesoscale Discussion | SPC | Blair, Bradford, Cambria, Cameron, Centre, Clarion and 25 more | 94 min |
| Jun 13, 7:21 PM EDT | Mesoscale Discussion | SPC | Blair, Bradford, Cambria, Cameron, Carbon, Centre and 20 more | 84 min |
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.