Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1498
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 12:19 PM EDT for 26 counties in Pennsylvania. It was in force for 116 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 12:19 PM EDT (16:19 UTC)
- Expired
- Aug 12, 2021, 2:15 PM EDT
- In force
- 116 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 60%
All 26 counties
Allegheny County, PA, Armstrong County, PA, Blair County, PA, Butler County, PA, Cambria County, PA, Cameron County, PA, Centre County, PA, Clarion County, PA, Clearfield County, PA, Clinton County, PA, Elk County, PA, Forest County, PA, Huntingdon County, PA, Indiana County, PA, Jefferson County, PA, Juniata County, PA, Lycoming County, PA, Mifflin County, PA, Montour County, PA, Northumberland County, PA, Perry County, PA, Snyder County, PA, Union County, PA, Venango County, PA, Washington County, PA, Westmoreland County, PA
The radar
The State College radar (KCCX), 58 km from the middle of the area, began a volume at 16:22 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
Pittsburgh, PA (KPIT), launched 12:00Z, 4.3 hours before the alert went out and 131 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
- 1075 J/kg
- Mixed-layer CIN
- -107 J/kg
- Mixed-layer LCL
- 890 m above ground
- 0-6 km bulk shear
- 21 kt
- 0-1 km storm-relative helicity
- 163 m²/s²
- 0-3 km storm-relative helicity
- 129 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 1.8
The text
As transmitted.
509
ACUS11 KWNS 121620
SWOMCD
SPC MCD 121619
PAZ000-121815-
Mesoscale Discussion 1498
NWS Storm Prediction Center Norman OK
1119 AM CDT Thu Aug 12 2021
Areas affected...western and central PA
Concerning...Severe potential...Watch possible
Valid 121619Z - 121815Z
Probability of Watch Issuance...60 percent
SUMMARY...Convective evolution is a bit uncertain but a gradual
increase in storm coverage is expected. The environment will
continue to destabilize and become more favorable for damaging and
localized severe gusts through the mid afternoon.
DISCUSSION...Visible-satellite imagery shows a cluster of
intensifying thunderstorms near the northeast OH/northwest PA border
moving east. A considerable patch of stratocumulus has been slow to
erode through the midday hours due in part to the high-quality
moisture present over the upper OH Valley east into central PA.
Surface temperatures are gradually warming into the low 80s with
dewpoints in the lower 70s. As temperatures warm into the mid-upper
80s, upwards of 3000+ J/kg MLCAPE is possible over southwest PA
northeastward into central PA this afternoon. The southern fringe
of stronger low- to mid-level flow is across western PA (around 30
kt at 3 km AGL). This slight enhancement in flow will aid in some
thunderstorm organization in the form of coherent clusters. Strong
to severe gusts (50-65 mph) will likely be the main threats with the
stronger storms. Timing of when a more widespread severe threat
will develop is a bit uncertain but it would seem a gradual increase
in storm coverage/intensity would occur over the next couple of
hours.
..Smith/Thompson.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CTP...PBZ...
LAT...LON 41477997 41677785 41347662 40447674 40067779 40118033
40778033 41477997SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 11:03 AM EDT | Mesoscale Discussion | SPC | Susquehanna | 2 hr |
| Aug 12, 1:11 PM EDT | Severe Thunderstorm Watch | SPC | Armstrong, Bedford, Blair, Cambria, Cameron, Centre and 27 more | 9 hr |
| Aug 12, 1:42 PM EDT | Severe Thunderstorm Watch | SPC | Bradford, Lackawanna, Luzerne, Pike, Susquehanna, Wayne and 1 more | 6 hr |
| Aug 12, 3:17 PM EDT | Mesoscale Discussion | SPC | Allegheny, Beaver, Butler, Crawford, Lawrence, Mercer and 1 more | 58 min |
| Aug 12, 3:48 PM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Crawford and 11 more | 6 hr |
| Aug 12, 6:22 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Blair, Butler, Cambria and 21 more | 83 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.