Alert archive / Pennsylvania / Mesoscale Discussions in 2012
Mesoscale Discussion 927
The Storm Prediction Center issued this mesoscale discussion at May 27, 2012, 6:34 PM EDT for 4 states. It was in force for 56 min.
The area
The outline as issued.
The facts
- Issued
- May 27, 2012, 6:34 PM EDT (22:34 UTC)
- Expired
- May 27, 2012, 7:30 PM EDT
- In force
- 56 min
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 40%
All 33 counties
Allegany County, MD, Baltimore County, MD, Carroll County, MD, City of Baltimore, MD, Frederick County, MD, Garrett County, MD, Howard County, MD, Montgomery County, MD, Washington County, MD, Adams County, PA, Bedford County, PA, Blair County, PA, Cambria County, PA, Cumberland County, PA, Fayette County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Mifflin County, PA, Perry County, PA, Somerset County, PA, Westmoreland County, PA, York County, PA, City of Winchester, VA, Clarke County, VA, Frederick County, VA, Loudoun County, VA, Berkeley County, WV, Hampshire County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV
The radar
The State College radar (KCCX), 104 km from the middle of the area, began a volume at 22:37 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, 10.6 hours before the alert went out and 145 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
- 247 J/kg
- Mixed-layer CIN
- -198 J/kg
- Mixed-layer LCL
- 935 m above ground
- 0-6 km bulk shear
- 27 kt
- 0-1 km storm-relative helicity
- -1 m²/s²
- 0-3 km storm-relative helicity
- 9 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
552
ACUS11 KWNS 272234
SWOMCD
SPC MCD 272234
PAZ000-MDZ000-VAZ000-WVZ000-272330-
MESOSCALE DISCUSSION 0927
NWS STORM PREDICTION CENTER NORMAN OK
0534 PM CDT SUN MAY 27 2012
AREAS AFFECTED...SRN PA...ERN MD...FAR NERN WV...FAR NRN VA
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 272234Z - 272330Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...ORGANIZED CONVECTIVE LINE EXPECTED TO PERSIST FOR THE NEXT
SEVERAL HOURS. CURRENT THINKING IS THAT THE LINE SHOULD GRADUALLY
WEAKEN OVER TIME AND DOWNSTREAM WW WILL NOT BE NEEDED. CONVECTIVE
TRENDS WILL BE MONITORED CLOSELY AND A WW MAY BE NEEDED IF A
WEAKENING TREND IS NOT NOTED.
DISCUSSION...LOOSELY ORGANIZED CONVECTIVE CLUSTER QUICKLY BECAME
ORGANIZED AS IT INTERACTED WITH A BOUNDARY DRAPED ACROSS CNTRL PA.
LATEST CCX RADAR IMAGERY SHOWED A LARGE AREA OF ENHANCED WINDS
ACROSS HUNTINGDON AND MIFFLIN COUNTIES. OBSERVATIONS AT AOO AND JST
REPORTED 41 KTS AND 36 KTS RESPECTIVELY. CONVECTION HAS SURGED SEWD
OVER THE PAST HOUR AND A POSSIBLE WEAKENING TREND MAY OCCUR DURING
THE NEXT 1-2 HOURS. WANING INSTABILITY ASSOCIATED WITH LOSS OF
DAYTIME HEATING WILL ALSO LIKELY RESULT IN A GRADUAL WEAKENING
TREND. MARGINAL SEVERE WIND THREAT SHOULD CONTINUE THROUGH THE
SOUTHERNMOST ROW OF PA COUNTIES /RECENTLY ADDED TO WW 306/. A TREND
TOWARDS INCREASED CONVECTION ON THE SRN END OF THE LINE /WITH
DECREASING TRENDS ON THE NRN END/ IS EXPECTED AS MORE INSTABILITY
REMAINS ACROSS PORTIONS OF NERN MD AND FAR NERN WV. EXPECTED
WEAKENING TREND AND THE CURRENT LACK OF SEVERE REPORTS PRECLUDES THE
NEED FOR A WW AT THIS TIME. HOWEVER...CONVECTIVE TRENDS WILL BE
MONITORED CLOSELY AND A WW MAY BE NEEDED IF A WEAKENING TREND IS NOT
NOTED.
..MOSIER/HART.. 05/27/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...CTP...LWX...PBZ...
LAT...LON 40357997 40497911 40637823 40717729 40107635 39077666
38947779 39617978 40357997SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 27, 1:41 PM EDT | Mesoscale Discussion | SPC | Allegany, Garrett, Washington | 64 min |
| May 27, 12:56 PM EDT | Mesoscale Discussion | SPC | Armstrong, Beaver, Butler, Clarion, Crawford, Erie and 5 more | 64 min |
| May 27, 1:33 PM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Crawford and 9 more | 5 hr |
| May 27, 4:12 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Blair, Butler, Cambria and 18 more | 63 min |
| May 27, 5:21 PM EDT | Severe Thunderstorm Watch | SPC | Adams, Bedford, Blair, Cambria, Centre, Clearfield and 21 more | 4 hr |
Nearby
Mesoscale Discussions in Pennsylvania, 2012Mesoscale Discussions in Maryland, 2012Mesoscale Discussions in West Virginia, 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.