Alert archive / Pennsylvania / Mesoscale Discussions in 2012
Mesoscale Discussion 1981
The Storm Prediction Center issued this mesoscale discussion at Sep 22, 2012, 3:09 PM EDT for 6 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 22, 2012, 3:09 PM EDT (19:09 UTC)
- Expired
- Sep 22, 2012, 5:15 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 60%
All 73 counties
Kent County, DE, New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Talbot County, MD, Bergen County, NJ, Burlington County, NJ, Camden County, NJ, Cumberland County, NJ, Essex County, NJ, Gloucester County, NJ, Hudson County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Morris County, NJ, Passaic County, NJ, Salem County, NJ, Somerset County, NJ, Sussex County, NJ, Union County, NJ, Warren County, NJ, Dutchess County, NY, New York County, NY, Orange County, NY, Putnam County, NY, Richmond County, NY, Rockland County, NY, Sullivan County, NY, Ulster County, NY, Adams County, PA, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester 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, Northampton County, PA, Philadelphia County, PA, Pike County, PA, Schuylkill County, PA, Wayne County, PA, York County, PA, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Manassas, VA, City of Manassas Park, VA, Fairfax County, VA, King George County, VA, Loudoun County, VA, Prince William County, VA
The radar
The Philadelphia radar (KDIX), 133 km from the middle of the area, began a volume at 19:12 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, 7.2 hours before the alert went out and 185 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
- 34 J/kg
- Mixed-layer CIN
- -233 J/kg
- Mixed-layer LCL
- 877 m above ground
- 0-6 km bulk shear
- 35 kt
- 0-1 km storm-relative helicity
- 175 m²/s²
- 0-3 km storm-relative helicity
- 158 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
679
ACUS11 KWNS 221910
SWOMCD
SPC MCD 221909
NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-222115-
MESOSCALE DISCUSSION 1981
NWS STORM PREDICTION CENTER NORMAN OK
0209 PM CDT SAT SEP 22 2012
AREAS AFFECTED...PARTS OF NRN VA/CNTRL MD/DE/ERN PA/NJ AND SERN
NY...INCLUDING THE URBAN CORRIDOR FROM WASHINGTON D.C. TO NEW YORK
CITY
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 221909Z - 222115Z
PROBABILITY OF WATCH ISSUANCE...60 PERCENT
SUMMARY...ALTHOUGH IT IS NOT YET CERTAIN THAT A WW WILL BE NEEDED
LATE THIS AFTERNOON...TRENDS ARE BEING MONITORED FOR AN INCREASING
SEVERE WEATHER THREAT WHICH COULD REQUIRE ONE WITHIN THE NEXT COUPLE
OF HOURS.
DISCUSSION...TO THIS POINT...CONVECTIVE DEVELOPMENT ALONG THE COLD
FRONT ADVANCING ACROSS THE NORTHERN APPALACHIANS REGION HAS BEEN
SUPPRESSED BY A WARM MID-LEVEL LAYER...GENERALLY BASED AROUND 500
MB. HOWEVER...THE WARM SECTOR BOUNDARY LAYER AHEAD OF THIS ACTIVITY
CONTINUES TO WARM AND MOISTEN ACROSS MUCH OF THE NORTHERN MID
ATLANTIC COAST REGION. AND STRENGTHENING MID-LEVEL FORCING FOR
UPWARD VERTICAL MOTION...DOWNSTREAM OF A SHORT WAVE IMPULSE NOW
TURNING EASTWARD INTO THE LOWER GREAT LAKES/UPPER OHIO VALLEY
REGION...MAY CONTRIBUTE TO DEEPENING/INTENSIFYING STORM DEVELOPMENT
ALONG THE FRONT BY THE 21-22Z TIME...AS IT APPROACHES THE URBAN
CORRIDOR...FROM NEAR/JUST WEST OF NEW YORK CITY SOUTHWARD INTO THE
BALTIMORE/WASHINGTON D.C. AREA.
WITH THE PRIMARY SURFACE CYCLONE CONTINUING TO MIGRATE NORTHWARD
ACROSS QUEBEC...LOW-LEVEL FLOW FIELDS ARE ONLY WEAK TO MODEST IN
STRENGTH...BUT THE EASTWARD PROGRESSION OF STRONGER MID/UPPER -LEVEL
WIND FIELDS /IN EXCESS OF 50 KT/ IS EXPECTED TO CONTRIBUTE TO
SUFFICIENT DEEP LAYER SHEAR FOR ORGANIZED CONVECTIVE DEVELOPMENT.
GRADUALLY...THE DOWNWARD TRANSFER OF MOMENTUM MAY LEAD TO AT LEAST A
FEW STRONG SURFACE GUSTS CAPABLE OF PRODUCING DAMAGE...BEFORE
CONVECTION WEAKENS THIS EVENING.
GIVEN THE RATHER MODEST NATURE OF THE LOW-LEVEL SHEAR...AND THE
LIMITED POTENTIAL FOR DISCRETE WARM SECTOR STORMS...THE RISK FOR
TORNADOES APPEARS LOW...BUT IT MAY NOT BE COMPLETELY NEGLIGIBLE.
..KERR/MEAD.. 09/22/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...OKX...ALY...PHI...BGM...AKQ...CTP...LWX...
LAT...LON 39187774 39717746 40827652 41587568 42097515 42277427
41837356 40717392 39497469 38647560 38247712 38637781
39187774SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 22, 6:31 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Elk and 7 more | 119 min |
Nearby
Mesoscale Discussions in Pennsylvania, 2012Mesoscale Discussions in New Jersey, 2012Mesoscale Discussions in Maryland, 2012Every mesoscale discussion in 2012
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.