Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 1872
The Storm Prediction Center issued this mesoscale discussion at Oct 16, 2021, 1:50 PM EDT for 5 states. It was in force for 115 min.
The area
The outline as issued.
The facts
- Issued
- Oct 16, 2021, 1:50 PM EDT (17:50 UTC)
- Expired
- Oct 16, 2021, 3:45 PM EDT
- In force
- 115 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 31 counties
Kent County, DE, New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Cecil County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Kent County, MD, Prince George's County, MD, Queen Anne's County, MD, Camden County, NJ, Gloucester County, NJ, Hunterdon County, NJ, Mercer County, NJ, Morris County, NJ, Salem County, NJ, Somerset County, NJ, Warren County, NJ, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Delaware County, PA, Lancaster County, PA, Lehigh County, PA, Montgomery County, PA, Northampton County, PA, Philadelphia County, PA, Arlington County, VA, City of Alexandria, VA
The radar
The Philadelphia radar (KDIX), 124 km from the middle of the area, began a volume at 17:53 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 12:00Z, 5.8 hours before the alert went out and 186 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
- 1259 m above ground
- 0-6 km bulk shear
- 41 kt
- 0-1 km storm-relative helicity
- 141 m²/s²
- 0-3 km storm-relative helicity
- 192 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
469
ACUS11 KWNS 161751
SWOMCD
SPC MCD 161750
NJZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-161945-
Mesoscale Discussion 1872
NWS Storm Prediction Center Norman OK
1250 PM CDT Sat Oct 16 2021
Areas affected...Southeastern PA...Eastern MD...NJ...DE
Concerning...Severe potential...Watch possible
Valid 161750Z - 161945Z
Probability of Watch Issuance...40 percent
SUMMARY...Line of showers and thunderstorms moving into eastern
PA/MD may produce a few damaging wind gusts as it continues eastward
over the next few hours.
DISCUSSION...A modest increase in reflectivity has been noted within
the showers/deeper convection along the leading edge of the cold
front moving through the region over the past half hour or so. The
downstream air mass has heated into the upper 70s/low 80s amid mid
60s dewpoints. As a result, a modest increase in buoyancy has
occurred, with mesoanalysis estimated MLCAPE around 250 J/kg from
eastern MD northward to the northern PA/NJ border vicinity. This
region is displaced south of the better forcing for ascent and
stronger flow aloft. However, enhanced low-level flow (sampled well
by the DOX and DIX VAD profiles) still appears strong enough to
support a damaging wind threat with any deeper, more persistent
cells. Uncertainty regarding overall coverage of strong storms
precludes higher watch probability, but convective trends will be
monitored closely.
..Mosier/Grams.. 10/16/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...BGM...CTP...LWX...
LAT...LON 40487634 41027584 41027453 40397453 38917547 38777721
39907655 40487634SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Oct 16, 11:06 AM EDT | Mesoscale Discussion | SPC | Berks, Bradford, Carbon, Columbia, Cumberland, Dauphin and 20 more | 114 min |
| Oct 16, 12:35 PM EDT | Severe Thunderstorm Watch | SPC | Lackawanna, Luzerne, Pike, Susquehanna, Wayne, Wyoming | 6 hr |
Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in Maryland, 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.