Alert archive / Pennsylvania / Mesoscale Discussions in 2012

Mesoscale Discussion 664

May 2, 20126 states

The Storm Prediction Center issued this mesoscale discussion at May 2, 2012, 4:56 PM EDT for 6 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 2, 2012, 4:56 PM EDT (20:56 UTC)
Expired: May 2, 2012, 7:00 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 58 counties

Allegany County, MD, Frederick County, MD, Garrett County, MD, Washington County, MD, Cattaraugus County, NY, Chautauqua County, NY, Ashtabula County, OH, Carroll County, OH, Columbiana County, OH, Cuyahoga County, OH, Geauga County, OH, Lake County, OH, Lorain County, OH, Mahoning County, OH, Medina County, OH, Portage County, OH, Stark County, OH, Summit County, OH, Trumbull County, OH, Wayne County, OH, Allegheny County, PA, Armstrong County, PA, Beaver County, PA, Bedford County, PA, Blair County, PA, Butler County, PA, Cambria County, PA, Clarion County, PA, Clearfield County, PA, Crawford County, PA, Elk County, PA, Erie County, PA, Fayette County, PA, Forest County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Indiana County, PA, Jefferson County, PA, Lawrence County, PA, McKean County, PA, Mercer County, PA, Somerset County, PA, Venango County, PA, Warren County, PA, Westmoreland County, PA, City of Winchester, VA, Clarke County, VA, Fauquier County, VA, Frederick County, VA, Loudoun County, VA, Warren County, VA, Berkeley County, WV, Hampshire County, WV, Hancock County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV

The radar

The Pittsburgh radar (KPBZ), 58 km from the middle of the area, began a volume at 20:56 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

Pittsburgh, PA (KPIT), launched 12:00Z, 8.9 hours before the alert went out and 70 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: 15 J/kg
Mixed-layer CIN: -73 J/kg
Mixed-layer LCL: 604 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 309 m²/s²
0-3 km storm-relative helicity: 317 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.

560 
ACUS11 KWNS 022057
SWOMCD
SPC MCD 022056
MDZ000-PAZ000-VAZ000-WVZ000-NYZ000-OHZ000-022300-

MESOSCALE DISCUSSION 0664
NWS STORM PREDICTION CENTER NORMAN OK
0356 PM CDT WED MAY 02 2012

AREAS AFFECTED...NORTHEAST OH/WESTERN PA/FAR WESTERN NY TO WV
PANHANDLE/NORTHERN VA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 022056Z - 022300Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...AT LEAST AN ISOLATED SEVERE THREAT MAY DEVELOP/POTENTIALLY
INCREASE THROUGH EARLY EVENING ACROSS PORTIONS OF NORTHEAST
OH/WESTERN PA AND EVENTUALLY FAR WESTERN NY...SOUTHEASTWARD TO
WESTERN MD/NORTHERN VA/WV PANHANDLE.

DISCUSSION...ALONG/SOUTHWEST OF A WARM FRONT...VISIBLE SATELLITE
TRENDS REFLECT SOME INCREASE IN THE CU FIELD OVER THE PAST FEW HOURS
ESPECIALLY ACROSS MUCH OF WESTERN PA AND ADJACENT PORTIONS OF
WESTERN MD/WV PANHANDLE AND NORTHERN VA...WITH A FEW TSTMS AS OF
21Z. ADDITIONALLY...WHILE THE CU FIELD HAS REMAINED RELATIVELY FLAT
FARTHER WEST-NORTHWEST...AN ASSORTMENT OF SHORT-TERM NUMERICAL
GUIDANCE SHOW RELATIVELY STRONG INDICATIONS OF THE POTENTIAL FOR AN
UPSWING IN DEEP CONVECTION BY EARLY EVENING ACROSS PORTIONS OF
NORTHEAST OH/NORTHWEST PA AND EVENTUALLY FAR WESTERN NY. THIS WOULD
LIKELY BE TIED OF THE SOUTHERN FRINGE OF A MID-LEVEL TROUGH OVER
ONTARIO...IN CONJUNCTION WITH DIFFERENTIAL HEATING/NEAR-LAKE
CONVERGENCE. SHOULD THIS OCCUR...A SEVERE THREAT MAINLY IN THE FORM
OF DAMAGING WINDS/SEVERE HAIL COULD INCREASE EARLY THIS EVENING SUCH
THAT A WATCH COULD BE WARRANTED.

..GUYER/CARBIN.. 05/02/2012

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

ATTN...WFO...BUF...CTP...LWX...PBZ...CLE...

LAT...LON   42807895 42257861 41147831 39317729 38487776 39067885
            40408028 40568153 40688200 40948234 41378260 41658199
            41828147 42307987 42807895

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 1, 9:33 PM EDT	Mesoscale Discussion	SPC	Adams, Athens, Belmont, Brown, Butler, Clark and 30 more	57 min
May 2, 3:46 PM EDT	Mesoscale Discussion	SPC	Auglaize, Champaign, Clark, Darke, Hardin, Logan and 6 more	119 min
May 2, 1:41 PM EDT	Mesoscale Discussion	SPC	Albemarle, Amelia, Amherst, Appomattox, Bedford, Brunswick and 46 more	2 hr

Nearby

Mesoscale Discussions in Pennsylvania, 2012 Mesoscale Discussions in Ohio, 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.