Alert archive / Pennsylvania / Mesoscale Discussions in 2012

Mesoscale Discussion 2079

October 19, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Oct 19, 2012, 4:48 PM EDT for 4 states. It was in force for 87 min.

The area

The outline as issued.

The facts

Issued: Oct 19, 2012, 4:48 PM EDT (20:48 UTC)
Expired: Oct 19, 2012, 6:15 PM EDT
In force: 87 min
Issued by: the Storm Prediction Center
Chance of a watch: 5%

All 53 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Cecil 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, Broome County, NY, Chenango County, NY, Cortland County, NY, Delaware County, NY, Sullivan County, NY, Tioga County, NY, Adams County, PA, Berks County, PA, Bradford County, PA, Carbon County, PA, Chester County, PA, Columbia County, PA, Dauphin County, PA, Lackawanna County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Luzerne County, PA, Monroe County, PA, Montour County, PA, Northampton County, PA, Northumberland County, PA, Pike County, PA, Schuylkill County, PA, Sullivan County, PA, Susquehanna County, PA, Wayne County, PA, Wyoming 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, Fauquier County, VA, Loudoun County, VA, Prince William County, VA

The radar

The Sterling radar (KLWX), 151 km from the middle of the area, began a volume at 20:50 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, 8.8 hours before the alert went out and 150 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 118 J/kg
Mixed-layer CIN: -26 J/kg
Mixed-layer LCL: 447 m above ground
0-6 km bulk shear: 85 kt
0-1 km storm-relative helicity: -19 m²/s²
0-3 km storm-relative helicity: 167 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

384 
ACUS11 KWNS 192048
SWOMCD
SPC MCD 192048 
NYZ000-PAZ000-NJZ000-DEZ000-MDZ000-DCZ000-VAZ000-192215-

MESOSCALE DISCUSSION 2079
NWS STORM PREDICTION CENTER NORMAN OK
0348 PM CDT FRI OCT 19 2012

AREAS AFFECTED...DELMARVA INTO SERN NY

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 192048Z - 192215Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...ISOLATED LOW-TOPPED SUPERCELLS MAY EVOLVE FROM NRN VA
ACROSS ERN PA INTO PORTIONS OF SERN NY.  ISOLATED WIND GUSTS ARE THE
PRIMARY THREAT.

DISCUSSION...EARLIER CLOUD COVER HAS BROKEN SUBSTANTIALLY ACROSS THE
DELMARVA NWD INTO ERN PA AND THIS HAS ALLOWED BOUNDARY LAYER TO
DEEPEN AS SFC TEMPERATURES WARMED INTO THE 70S.  RESULTANT STEEPER
LOW LEVEL LAPSE RATES HAVE AIDED SHALLOW CONVECTION AND EVEN A FEW
DEEPER UPDRAFTS THAT ARE NOW PRODUCING LIGHTNING...ESPECIALLY NE OF
HARRISBURG PA.  GIVEN THE STRONG SHEAR IN PLACE CURRENT THINKING IS
THE MORE SUSTAINED UPDRAFTS MAY EXHIBIT BRIEF SUPERCELL
CHARACTERISTICS BUT INSTABILITY SHOULD PROVE INADEQUATE TO WARRANT
MORE THAN ISOLATED MARGINAL SEVERE WIND GUSTS.

..DARROW/WEISS.. 10/19/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...ALY...PHI...BGM...AKQ...CTP...LWX...

LAT...LON   38687789 42737618 42177445 38387632 38687789

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Oct 18, 8:55 PM EDT	Mesoscale Discussion	SPC	Albemarle, Amelia, Amherst, Appomattox, Bedford, Brunswick and 57 more	2 hr

Nearby

Mesoscale Discussions in Pennsylvania, 2012 Mesoscale Discussions in Maryland, 2012 Mesoscale Discussions in Virginia, 2012 Every 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.