Alert archive / Pennsylvania / Mesoscale Discussions in 2011
Mesoscale Discussion 802
The Storm Prediction Center issued this mesoscale discussion at May 18, 2011, 2:34 PM EDT for 12 counties in New Jersey; Richmond County, New York; 18 counties in Pennsylvania. It was in force for 56 min.
The area
The outline as issued.
The facts
- Issued
- May 18, 2011, 2:34 PM EDT (18:34 UTC)
- Expired
- May 18, 2011, 3:30 PM EDT
- In force
- 56 min
- Issued by
- the Storm Prediction Center
All 31 counties
Burlington County, NJ, Essex County, NJ, Hunterdon County, NJ, Mercer County, NJ, Middlesex County, NJ, Monmouth County, NJ, Morris County, NJ, Ocean County, NJ, Somerset County, NJ, Sussex County, NJ, Union County, NJ, Warren County, NJ, Richmond County, NY, Berks County, PA, Bucks County, PA, Carbon County, PA, Columbia County, PA, Lackawanna County, PA, Lebanon County, PA, Lehigh County, PA, Luzerne County, PA, Monroe County, PA, Montgomery County, PA, Montour County, PA, Northampton County, PA, Northumberland County, PA, Philadelphia County, PA, Pike County, PA, Schuylkill County, PA, Sullivan County, PA, Wyoming County, PA
The radar
The Philadelphia radar (KDIX), 94 km from the middle of the area, began a volume at 18:36 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
Phillips Aaf/Abe, MD (KAPG), launched 12:00Z, 6.6 hours before the alert went out and 146 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
- 79 J/kg
- Mixed-layer CIN
- -31 J/kg
- Mixed-layer LCL
- 561 m above ground
- 0-6 km bulk shear
- 31 kt
- 0-1 km storm-relative helicity
- 66 m²/s²
- 0-3 km storm-relative helicity
- 169 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.4
The text
As transmitted, in the capitals the NWS used until 2016.
655
ACUS11 KWNS 181834
SWOMCD
SPC MCD 181834
NJZ000-NYZ000-PAZ000-181930-
MESOSCALE DISCUSSION 0802
NWS STORM PREDICTION CENTER NORMAN OK
0134 PM CDT WED MAY 18 2011
AREAS AFFECTED...PARTS OF ERN PA AND CENTRAL/NRN NJ
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 181834Z - 181930Z
WW IS POSSIBLE THIS AFTERNOON ACROSS PARTS OF ERN PA AND CENTRAL/NRN
NJ. THIS POTENTIAL WILL BE GREATER IF INSTABILITY INCREASES BEYOND
THE CURRENT MARGINAL VALUES AND RADAR TRENDS SUGGEST MORE PERSISTENT
UPDRAFTS.
SURFACE ANALYSES INDICATED A CORRIDOR OF GREATER MOISTURE EXTENDING
INLAND FROM THE NJ COAST INTO ERN PA...WITH VALUES IN THE LOWER 60S
ACROSS MUCH OF NJ INTO EAST CENTRAL/SERN PA AND NEAR 60 IN NERN PA.
ALTHOUGH CLOUDINESS HAS LIMITED SURFACE HEATING/ DESTABILIZATION AND
WEAKER MIDLEVEL LAPSE RATES EXIST ACROSS THIS AREA...MUCAPE IS
RANGING FROM 500-1000 J/KG. THE MARGINAL INSTABILITY AND LAPSE
RATES SUGGEST INDIVIDUAL STORMS MAY STRUGGLE TO ATTAIN PERSISTENT
UPDRAFTS...AND THUS POSE A SUFFICIENT THREAT FOR STRONG TO SEVERE
TSTM COVERAGE THAT WOULD WARRANT A SEVERE WEATHER WATCH.
DESPITE THE MARGINAL INSTABILITY...KINEMATICS ARE FAVORABLE FOR
STORM ORGANIZATION AND SOME ROTATION. TRENDS IN LOW LEVEL FLOW PER
OBJECTIVE ANALYSES AND AREA WSR-88D VWPS INDICATED AN INCREASE IN
WIND SPEEDS WITH SOME BACKING TO SELY. THIS IS RESULTING IN AN
INCREASE IN LOW LEVEL SHEAR FOR STORM ROTATION. STRONGER ESELY
MIDLEVEL WINDS/DEEP SHEAR WILL CONTINUE TO INCREASE THIS AFTERNOON
AS THE ATTENDANT CLOSED LOW LOCATED OVER THE CENTRAL APPALACHIANS
SHIFTS NWD. REGIONAL RADAR IMAGERY SHOWED AN AREA OF SHOWERS/
EMBEDDED TSTMS EXTENDING FROM SERN PA THROUGH CENTRAL/NRN NJ AND
OFFSHORE...WITH A FEW OF THE STORMS INDICATING PERIODIC LOW LEVEL
ROTATIONAL COUPLETS.
..PETERS.. 05/18/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...OKX...PHI...BGM...CTP...
LAT...LON 39697423 39987539 40347657 40807703 41587662 41697574
41317473 40887420 40457406 39827398 39697423SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 18, 12:55 PM EDT | Severe Thunderstorm Watch | SPC | Cape May, Cumberland, Salem | 8 hr |
| May 18, 3:08 PM EDT | Mesoscale Discussion | SPC | Atlantic, Burlington, Camden, Cape May, Cumberland, Essex and 14 more | 67 min |
| May 18, 11:55 AM EDT | Mesoscale Discussion | SPC | Adams, Allegheny, Beaver, Bedford, Blair, Cambria and 8 more | 65 min |
| May 18, 6:01 PM EDT | Mesoscale Discussion | SPC | Adams, Allegheny, Beaver, Bedford, Butler, Fayette and 7 more | 89 min |
Nearby
Mesoscale Discussions in Pennsylvania, 2011Mesoscale Discussions in New Jersey, 2011Mesoscale Discussions in New York, 2011Every mesoscale discussion in 2011
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.