Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1507
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 10:08 PM EDT for 6 counties in New Jersey; 28 counties in Pennsylvania. It was in force for 67 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 10:08 PM EDT (02:08 UTC)
- Expired
- Aug 12, 2021, 11:15 PM EDT
- In force
- 67 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 34 counties
Hunterdon County, NJ, Mercer County, NJ, Morris County, NJ, Somerset County, NJ, Sussex County, NJ, Warren County, NJ, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Delaware County, PA, Lackawanna County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Luzerne County, PA, Monroe County, PA, Montgomery County, PA, Montour County, PA, Northampton County, PA, Northumberland County, PA, Perry County, PA, Philadelphia County, PA, Pike County, PA, Schuylkill County, PA, Snyder County, PA, Sullivan County, PA, Susquehanna County, PA, Wayne County, PA, Wyoming County, PA, York County, PA
The radar
The Philadelphia radar (KDIX), 132 km from the middle of the area, began a volume at 02:08 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, 2.1 hours before the alert went out and 232 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
- 2808 J/kg
- Mixed-layer CIN
- -24 J/kg
- Mixed-layer LCL
- 1565 m above ground
- 0-6 km bulk shear
- 15 kt
- 0-1 km storm-relative helicity
- 38 m²/s²
- 0-3 km storm-relative helicity
- 153 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 4.9
The text
As transmitted.
300
ACUS11 KWNS 130209
SWOMCD
SPC MCD 130208
NYZ000-NJZ000-PAZ000-DEZ000-130315-
Mesoscale Discussion 1507
NWS Storm Prediction Center Norman OK
0908 PM CDT Thu Aug 12 2021
Areas affected...eastern PA
Concerning...Severe potential...Watch unlikely
Valid 130208Z - 130315Z
Probability of Watch Issuance...20 percent
SUMMARY...Cluster of storms ongoing across central PA may pose a
risk for damaging wind gusts for a few more hours before weakening
this evening.
DISCUSSION...As of 0150 UTC, regional radar imagery showed a line of
strong thunderstorms across north-central PA moving east at 45 mph.
Associated with a large band of storms that has recently weakened
farther west, some resurgence has been noted with the lead cluster
west of Scranton, PA. Recent IR imagery showed a localized area of
cooling cloud tops indicating some additional storm
development/strengthening may briefly be possible over the next
couple of hours. Ahead of the line, SPC mesoanalyis indicates an
unstable environment is in place with 2500-3000 J/kg of MLCAPE.
However, convective inhibition is also rapidly increasing as surface
temperatures cool. Vertical shear while not strong at 25 kts is
oriented perpendicular to the motion of the cold pool supporting
strong convergence along the leading edge. Thus, it appears possible
that some severe risk in the form of damaging wind gusts may
continue for a few more hours before nocturnal stabilization
diminishes the threat.
..Lyons.. 08/13/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...OKX...PHI...BGM...CTP...
LAT...LON 40327746 41797639 41887542 41637448 41107439 40537452
40097477 39907494 39827543 39857627 39877706 40327746SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 13, 6:02 PM EDT | Mesoscale Discussion | SPC | Atlantic, Cape May, Cumberland, Gloucester, Salem | 58 min |
| Aug 13, 12:33 PM EDT | Mesoscale Discussion | SPC | Adams, Cumberland, Dauphin, Franklin, Fulton, Lancaster and 3 more | 87 min |
| Aug 13, 1:11 PM EDT | Severe Thunderstorm Watch | SPC | Adams, Berks, Chester, Cumberland, Dauphin, Franklin and 6 more | 7 hr |
| Aug 13, 2:48 PM EDT | Mesoscale Discussion | SPC | Bradford, Cameron, Clinton, Lycoming, Potter, Sullivan and 2 more | 87 min |
| Aug 13, 3:29 PM EDT | Severe Thunderstorm Watch | SPC | Bradford, Clinton, Columbia, Lackawanna, Luzerne, Lycoming and 11 more | 7 hr |
| Aug 13, 4:46 PM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 9 more | 5 hr |
| Aug 13, 4:48 PM EDT | Mesoscale Discussion | SPC | Chester | 87 min |
| Aug 13, 7:14 PM EDT | Mesoscale Discussion | SPC | Bradford, Columbia, Lackawanna, Luzerne, Lycoming, Monroe and 9 more | 61 min |
| Aug 13, 7:49 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Butler, Cambria, Clarion and 13 more | 56 min |
Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in New Jersey, 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.