Alert archive / Pennsylvania / Mesoscale Discussions in 2021
Mesoscale Discussion 127
The Storm Prediction Center issued this mesoscale discussion at Feb 22, 2021, 7:48 AM EST for Washington County, Maryland; 4 counties in New Jersey; 30 counties in Pennsylvania. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Feb 22, 2021, 7:48 AM EST (12:48 UTC)
- Expired
- Feb 22, 2021, 11:45 AM EST
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Heavy snow
All 35 counties
Washington County, MD, Hunterdon County, NJ, Morris County, NJ, Sussex County, NJ, Warren County, NJ, Adams County, PA, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Juniata County, PA, Lackawanna County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Luzerne County, PA, Lycoming County, PA, Mifflin County, PA, Monroe County, PA, Montgomery County, PA, Montour County, PA, Northampton County, PA, Northumberland County, PA, Perry County, PA, Pike County, PA, Schuylkill County, PA, Snyder County, PA, Sullivan County, PA, Union County, PA, Wyoming County, PA, York County, PA
The radar
The State College radar (KCCX), 148 km from the middle of the area, began a volume at 12:50 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, 0.8 hours before the alert went out and 191 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
- 1420 m above ground
- 0-6 km bulk shear
- 91 kt
- 0-1 km storm-relative helicity
- 461 m²/s²
- 0-3 km storm-relative helicity
- 475 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
203
ACUS11 KWNS 221249
SWOMCD
SPC MCD 221248
NJZ000-PAZ000-MDZ000-WVZ000-221645-
Mesoscale Discussion 0127
NWS Storm Prediction Center Norman OK
0648 AM CST Mon Feb 22 2021
Areas affected...eastern half of PA...parts of northwest NJ
Concerning...Heavy snow
Valid 221248Z - 221645Z
SUMMARY...Heavy snowfall rates around 1 inch per hour are forecast
this morning with the duration around 2-3 hours. Localized heavier
bursts are possible (up to 1.5 inches per hour).
DISCUSSION...Radar mosaic early this morning shows a precipitation
shield moving east across the central Appalachians ahead of a
migratory mid-level shortwave trough (per water-vapor imagery).
Strong low-level warm air advection (implied by area 88D VAD data)
and strong differential cyclonic vorticity advection will result in
a several hour window of enhanced large-scale ascent over the
eastern half of PA through the late morning. Model guidance is in
relatively good agreement in showing snowfall rates at or slightly
higher than 1 inch per hour developing first over the higher terrain
in central PA and then spreading east. Model soundings imply the
heaviest rates will probably occur near State College between 8-9am
EST and 11am-12pm EST near Reading, PA.
..Smith.. 02/22/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...BGM...CTP...LWX...
LAT...LON 39477788 40717797 41867707 41247469 40817451 40347491
39837593 39477788Nearby
Mesoscale Discussions in Pennsylvania, 2021Mesoscale Discussions in New Jersey, 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.