Alert archive / Pennsylvania / Mesoscale Discussions in 2012

Mesoscale Discussion 2234

December 26, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Dec 26, 2012, 11:40 AM EST for 4 states. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Dec 26, 2012, 11:40 AM EST (16:40 UTC)
Expired: Dec 26, 2012, 5:45 PM EST
In force: 6 hr
Issued by: the Storm Prediction Center

All 40 counties

Allegany County, NY, Cattaraugus County, NY, Ashland County, OH, Carroll County, OH, Columbiana County, OH, Geauga County, OH, Holmes County, OH, Mahoning County, OH, Medina County, OH, Portage County, OH, Richland County, OH, Stark County, OH, Summit County, OH, Trumbull County, OH, Tuscarawas County, OH, Wayne County, OH, Allegheny County, PA, Armstrong County, PA, Beaver County, PA, Butler County, PA, Cameron County, PA, Centre County, PA, Clarion County, PA, Clearfield County, PA, Clinton County, PA, Crawford County, PA, Elk County, PA, Forest County, PA, Indiana County, PA, Jefferson County, PA, Lawrence County, PA, Lycoming County, PA, McKean County, PA, Mercer County, PA, Potter County, PA, Tioga County, PA, Union County, PA, Venango County, PA, Warren County, PA, Hancock County, WV

The radar

The Pittsburgh radar (KPBZ), 71 km from the middle of the area, began a volume at 16:42 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, 4.7 hours before the alert went out and 81 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 712 m above ground
0-6 km bulk shear: 43 kt
0-1 km storm-relative helicity: 174 m²/s²
0-3 km storm-relative helicity: 143 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

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

102 
ACUS11 KWNS 261641
SWOMCD
SPC MCD 261640
PAZ000-NYZ000-WVZ000-OHZ000-262245-

MESOSCALE DISCUSSION 2234
NWS STORM PREDICTION CENTER NORMAN OK
1040 AM CST WED DEC 26 2012

AREAS AFFECTED...NERN OH...PARTS OF CNTRL/WRN/NRN PA...SWRN NY

CONCERNING...HEAVY SNOW

VALID 261640Z - 262245Z

SUMMARY...HEAVY SNOW WITH RATES OF 1-2 IN/HR IS EXPECTED TO DEVELOP
NEWD THROUGH THE AFTERNOON.

DISCUSSION...A BAND OF STRONG/DEEP ISENTROPIC ASCENT WITHIN THE WARM
CONVEYOR BELT OF THE LARGE EXTRATROPICAL CYCLONE OVER THE ERN CONUS
WILL SHIFT NEWD THROUGH THE DAY IN TANDEM WITH THE MOTION OF THE
CYCLONE CENTER. AS THE ASCENT MOVES OVER PROGRESSIVELY COLDER/DEEPER
SUBFREEZING LAYER PER REGIONAL 12Z RAOBS...INCREASED CHANCES FOR
HEAVY SNOW WILL OCCUR INTO THE AFTERNOON FROM N-CNTRL OH EWD ACROSS
CNTRL PA AND NWD INTO SWRN NY.

THE HEAVY SNOW WILL BE MOST LIKELY AFTER 18Z OVER N-CNTRL OH INTO
NWRN PA AND GRADUALLY SHIFT NEWD TOWARD SWRN NY AND CNTRL/N-CNTRL PA
LATER THIS AFTERNOON INTO THE EARLY EVENING. FORECAST SOUNDINGS
SUGGEST THAT THE ASCENT WILL ALIGN WITH DENDRITIC GROWTH ZONES
ENCOMPASSING DEPTHS OF AROUND 50 MB CENTERED BETWEEN THE 600- AND
500-MB LEVELS...WHICH WILL OVERLIE ISOTHERMAL LAYERS ABOVE THE
900-MB LEVEL. THESE FACTORS WILL SUPPORT EFFICIENT SNOW GROWTH AND
SNOWFALL RATES OF 1-2 IN/HR. ALSO...NARROW ELEVATED CAPE LAYERS
FEATURING MEAGER BUOYANCY COULD SUPPORT A MODEST CONVECTIVE
ENHANCEMENT TO PRECIPITATION RATES. A LIGHTNING STRIKE OR TWO CANNOT
BE RULED OUT WITH THE HIGHEST SNOWFALL RATES.

..COHEN.. 12/26/2012

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

ATTN...WFO...BGM...BUF...CTP...PBZ...CLE...

LAT...LON   40567797 40448011 40358168 40498256 40938269 41338225
            41828071 42447870 42247730 41097663 40567797

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 26, 2:14 PM EST	Mesoscale Discussion	SPC	Albany, Allegany, Broome, Cattaraugus, Cayuga, Chemung and 35 more	6 hr
Dec 26, 4:39 PM EST	Mesoscale Discussion	SPC	Rensselaer, Washington	5 hr
Dec 26, 3:25 AM EST	Mesoscale Discussion	SPC	Auglaize, Butler, Champaign, Clark, Darke, Greene and 9 more	6 hr
Dec 26, 6:46 AM EST	Mesoscale Discussion	SPC	Athens, Washington	4 hr
Dec 26, 9:57 AM EST	Mesoscale Discussion	SPC	Coshocton, Delaware, Fairfield, Fayette, Franklin, Guernsey and 8 more	5 hr
Dec 26, 10:39 AM EST	Mesoscale Discussion	SPC	Allen, Auglaize, Champaign, Crawford, Darke, Defiance and 21 more	6 hr
Dec 26, 12:48 PM EST	Mesoscale Discussion	SPC	Adams, Bedford, Berks, Bradford, Bucks, Carbon and 27 more	6 hr

Nearby

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