Alert archive / Maryland / Mesoscale Discussions in 2011

Mesoscale Discussion 798

May 17, 20115 states

The Storm Prediction Center issued this mesoscale discussion at May 17, 2011, 6:27 PM EDT for 5 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: May 17, 2011, 6:27 PM EDT (22:27 UTC)
Expired: May 17, 2011, 8:30 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center

All 40 counties

Kent County, DE, New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Caroline County, MD, Carroll County, MD, Cecil County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Talbot County, MD, Washington County, MD, Adams County, PA, Cumberland County, PA, Franklin County, PA, Fulton County, PA, Lancaster County, PA, York County, PA, Arlington County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Manassas, VA, City of Manassas Park, VA, City of Winchester, VA, Clarke County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Loudoun County, VA, Prince William County, VA, Warren County, VA, Berkeley County, WV, Jefferson County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 71 km from the middle of the area, began a volume at 22:27 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, 10.5 hours before the alert went out and 65 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: 65 J/kg
Mixed-layer CIN: -5 J/kg
Mixed-layer LCL: 490 m above ground
0-6 km bulk shear: 30 kt
0-1 km storm-relative helicity: 87 m²/s²
0-3 km storm-relative helicity: 118 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.

455 
ACUS11 KWNS 172227
SWOMCD
SPC MCD 172227 
NJZ000-DEZ000-PAZ000-MDZ000-DCZ000-VAZ000-WVZ000-180030-

MESOSCALE DISCUSSION 0798
NWS STORM PREDICTION CENTER NORMAN OK
0527 PM CDT TUE MAY 17 2011

AREAS AFFECTED...PA/NJ/MD/DE/VA/WV/DC

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 172227Z - 180030Z

AREAS FROM THE NRN CHESAPEAKE BAY AND DELAWARE BAY INLAND ACROSS
SERN PA...THE WV PANHANDLE...NRN VA AND D.C...ARE BEING MONITORED
FOR ORGANIZED TSTM DEVELOPMENT. CONDITIONS IN THESE AREAS COULD
FAVOR PERSISTENT STORMS WITH THE POTENTIAL FOR LOW LEVEL STORM
ROTATION AND POSSIBLY A BRIEF TORNADO. HOWEVER...LIMITED STORM
COVERAGE AND INSTABILITY SUGGEST THAT TEMPORAL NATURE OF THIS THREAT
IS LIKELY TOO LIMITED FOR A WATCH.

ASCENT ASSOCIATED WITH VORT LOBE PIVOTING THROUGH THE NERN QUADRANT
OF MID/UPPER LEVEL LOW APPEARS TO HAVE AIDED A BAND OF TSTMS NOW 
DEVELOPING NNWWD INTO SRN/CNTRL PA. IN THE WAKE OF THIS
ACTIVITY...LOW LEVEL AIRMASS REMAINS MOIST AND WEAKLY UNSTABLE WITH
CONFLUENT LOW ELY LEVEL FLOW TOPPED BY 50KT MID LEVEL JET STREAK
ROTATING AROUND THE UPPER LOW. IF ADDITIONAL DISCRETE STORMS CAN
INITIATE OVER THE NEXT FEW HOURS...NWWD/NWD-MOVING STORM UPDRAFTS
WILL EXIST IN KINEMATIC REGIME SUPPORTIVE OF LOW LEVEL STORM
ROTATION WITH EFFECTIVE SRH AROUND 200 J PER KG AND RELATIVELY LOW
LFC FAVORING THE POTENTIAL FOR A TORNADO. OVERALL SCENARIO APPEARS
TO BE TEMPERED BY THE POTENTIAL THAT DEEPER ASCENT MAY BE ON THE
WANE WITH THE PASSAGE OF THE UPPER VORT LOBE AND ASSOCIATED DPVA.
NONETHELESS...ONGOING ISOLATED STORMS MAY POSE SOME THREAT AND ANY
UPWARD TRENDS IN STORM COVERAGE MAY WARRANT A REASSESSMENT.

..CARBIN.. 05/17/2011

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

ATTN...WFO...PHI...AKQ...CTP...LWX...

LAT...LON   40107604 39717540 39137542 38667579 38447730 38617797
            39037848 39817840 40207768 40107604

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 17, 11:14 AM EDT	Mesoscale Discussion	SPC	Calvert, Charles, Saint Mary's	2 hr

Nearby

Mesoscale Discussions in Maryland, 2011 Mesoscale Discussions in Virginia, 2011 Mesoscale Discussions in Pennsylvania, 2011 Every 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.