Alert archive / Virginia / Mesoscale Discussions in 2011

Mesoscale Discussion 463

April 16, 201117 counties in Maryland; 28 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 16, 2011, 8:12 PM EDT for 17 counties in Maryland; 28 counties in Virginia. It was in force for 63 min.

The area

The outline as issued.

The facts

Issued: Apr 16, 2011, 8:12 PM EDT (00:12 UTC)
Expired: Apr 16, 2011, 9:15 PM EDT
In force: 63 min
Issued by: the Storm Prediction Center

All 45 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Dorchester County, 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, Saint Mary's County, MD, Talbot County, MD, Arlington County, VA, Caroline County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Manassas, VA, City of Manassas Park, VA, Culpeper County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Goochland County, VA, Hanover County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Northumberland County, VA, Orange County, VA, Prince William County, VA, Richmond County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA

The radar

The Sterling radar (KLWX), 72 km from the middle of the area, began a volume at 00:15 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 00:00Z, 0.2 hours before the alert went out and 67 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: 132 J/kg
Mixed-layer CIN: -18 J/kg
Mixed-layer LCL: 547 m above ground
0-6 km bulk shear: 77 kt
0-1 km storm-relative helicity: 574 m²/s²
0-3 km storm-relative helicity: 593 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.5

Open this sounding in Storm Lab

The text

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

807 
ACUS11 KWNS 170013
SWOMCD
SPC MCD 170012
MDZ000-VAZ000-DCZ000-170115-

MESOSCALE DISCUSSION 0463
NWS STORM PREDICTION CENTER NORMAN OK
0712 PM CDT SAT APR 16 2011

AREAS AFFECTED...DC...NRN VA...ERN MD

CONCERNING...TORNADO WATCH 151...

VALID 170012Z - 170115Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 151 CONTINUES.

BROKEN QLCS STRUCTURES CONTINUE TO DEVELOP ACROSS THE NRN AND CNTRL
SECTIONS OF WW151 AND MOVE NEWD AS THE SFC MOIST AXIS EXPANDS N/NEWD
ACROSS THE MIDDLE ATLANTIC AHEAD OF AN APPROACHING COLD FRONT AND
PREFRONTAL TROUGH. STRONG DEEP-LAYER AND LOW-LEVEL SHEAR HAS ALLOWED
LEWP AND OCCASIONAL SUPERCELL STRUCTURES TO EVOLVE INVOF A WARM
FRONT. THIS WARM FRONT EXTENDS ROUGHLY FROM A SFC LOW OVER NRN VA TO
THE BALTIMORE AREA AND FARTHER SEWD OVER THE SRN TIP OF LOWER SRN
MD...AND WILL REMAIN A FOCUSING MECHANISM FOR CONTINUED TORNADO
POTENTIAL AS IT LIFTS NEWD WITH TIME. THE TORNADO POTENTIAL WILL
ALSO EXTEND FARTHER SOUTH INTO THE WEAKLY UNSTABLE SECTOR GIVEN
EFFECTIVE SRH VALUES AOA 700 M2/S2. STRONG FLOW JUST ABOVE THE SFC
WILL ALLOW FOR A CONTINUED DMGG WIND POTENTIAL...AS WELL. THE
CONVECTION IS EXPECTED TO CROSS THE BALTIMORE AND DC METRO AREAS
BETWEEN 0030Z AND 0100Z...AND COULD PERSIST PAST THE SCHEDULED
EXPIRATION TIME OF 01Z ACROSS PORTIONS OF NERN VA AND ERN MD.
THUS...THE WW MAY NEED TO BE LOCALLY EXTENDED IN TIME ACROSS THE
NERN QUARTER OF THE WW 151 AREA.

..COHEN.. 04/17/2011

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

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

LAT...LON   37647732 37647784 37727822 37987849 38317836 38917804
            39547737 39627666 39487586 38587579 37997602 37637688
            37647732

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 16, 9:58 PM EDT	Mesoscale Discussion	SPC	Caroline, Queen Anne's	62 min

Nearby

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