Alert archive / Pennsylvania / Mesoscale Discussions in 2012

Mesoscale Discussion 920

May 27, 2012Chautauqua County, New York; 5 counties in Ohio; 11 counties in Pennsylvania

The Storm Prediction Center issued this mesoscale discussion at May 27, 2012, 12:56 PM EDT for Chautauqua County, New York; 5 counties in Ohio; 11 counties in Pennsylvania. It was in force for 64 min.

The area

The outline as issued.

The facts

Issued
May 27, 2012, 12:56 PM EDT (16:56 UTC)
Expired
May 27, 2012, 2:00 PM EDT
In force
64 min
Issued by
the Storm Prediction Center
Chance of a watch
40%

Counties Chautauqua County, NY, Ashtabula County, OH, Geauga County, OH, Lake County, OH, Mahoning County, OH, Trumbull County, OH, Armstrong County, PA, Beaver County, PA, Butler County, PA, Clarion County, PA, Crawford County, PA, Erie County, PA, Forest County, PA, Lawrence County, PA, Mercer County, PA, Venango County, PA, Warren County, PA

The radar

The Pittsburgh radar (KPBZ), 128 km from the middle of the area, began a volume at 16:58 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

The nearest sounding before it

Pittsburgh, PA (KPIT), launched 12:00Z, 4.9 hours before the alert went out and 141 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-pSkew-T log-p diagram, Pittsburgh, PA at 12:00Z on 2012-05-27Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 993 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Pittsburgh, PA at 12:00Z on 2012-05-27The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 46 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
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
993 J/kg
Mixed-layer CIN
-88 J/kg
Mixed-layer LCL
1085 m above ground
0-6 km bulk shear
16 kt
0-1 km storm-relative helicity
46 m²/s²
0-3 km storm-relative helicity
47 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.

747 
ACUS11 KWNS 271657
SWOMCD
SPC MCD 271656
PAZ000-NYZ000-OHZ000-271800-

MESOSCALE DISCUSSION 0920
NWS STORM PREDICTION CENTER NORMAN OK
1156 AM CDT SUN MAY 27 2012

AREAS AFFECTED...WRN NY...NERN OH...NWRN PA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 271656Z - 271800Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...THE LEADING EDGE OF AN MCS IS EXPECTED TO IMPACT FAR NERN
OH...NWRN PA AND WRN NY OVER THE NEXT HOUR. THE PRIMARY THREAT /NOW
OVER SRN ONTARIO/ WILL PROGRESS INTO THE AREA SHORTLY
THEREAFTER...AND MAY NECESSITATE A WW ISSUANCE SHOULD MORE
ORGANIZATION BECOME APPARENT.

DISCUSSION...AN ONGOING MCS ACROSS SRN ONTARIO IS SHOWING SIGNS OF
RENEWED VIGOR OVER THE PAST HOUR AS DIURNAL HEATING CONTINUES TO
DESTABILIZE THE DOWNSTREAM AIR MASS. GIVEN WELL ABOVE NORMAL PWAT
VALUES...CONTINUED CONVECTIVE DEVELOPMENT APPEARS LIKELY AS THE MCS
PROGRESSES ESEWD. STEEPENING LOW LEVEL LAPSE RATES MAY SUPPORT DMGG
WINDS...THOUGH WEAK LOW LEVEL FLOW MAY HINDER MORE
WIDESPREAD/SIGNIFICANT WIND POTENTIAL. GIVEN MODEST WNWLYS
ALOFT...THE CONTINUATION OF A SEMI-ORGANIZED MCS APPEARS POSSIBLE.

..HURLBUT/CARBIN.. 05/27/2012

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

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

LAT...LON   42597937 41767874 40957914 40528001 40718071 41408130
            42058114 42488040 42597937

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 27, 1:33 PM EDTSevere Thunderstorm WatchSPCAshtabula, Carroll, Columbiana, Cuyahoga, Geauga, Harrison and 8 more5 hr
May 27, 1:41 PM EDTMesoscale DiscussionSPCJefferson64 min
May 27, 4:12 PM EDTMesoscale DiscussionSPCAllegheny, Armstrong, Beaver, Blair, Butler, Cambria and 18 more63 min
May 27, 5:21 PM EDTSevere Thunderstorm WatchSPCAdams, Bedford, Blair, Cambria, Centre, Clearfield and 21 more4 hr
May 27, 6:34 PM EDTMesoscale DiscussionSPCAdams, Bedford, Blair, Cambria, Cumberland, Fayette and 9 more56 min

Nearby

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