Alert archive / Virginia / Mesoscale Discussions in 2011

Mesoscale Discussion 461

April 16, 20116 states

The Storm Prediction Center issued this mesoscale discussion at Apr 16, 2011, 6:38 PM EDT for 6 states. It was in force for 97 min.

The area

The outline as issued.

The facts

Issued: Apr 16, 2011, 6:38 PM EDT (22:38 UTC)
Expired: Apr 16, 2011, 8:15 PM EDT
In force: 97 min
Issued by: the Storm Prediction Center

All 82 counties

Kent County, DE, New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Cecil 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, Washington County, MD, Cumberland County, NJ, Gloucester County, NJ, Salem County, NJ, Adams County, PA, Berks County, PA, Chester County, PA, Cumberland County, PA, Dauphin County, PA, Delaware County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Mifflin County, PA, Montgomery County, PA, Northumberland County, PA, Perry County, PA, Schuylkill County, PA, Snyder County, PA, York County, PA, Albemarle County, VA, Arlington County, VA, Augusta County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Harrisonburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Greene County, VA, King George County, VA, Loudoun County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Westmoreland County, VA, Berkeley County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Morgan County, WV

The radar

The Sterling radar (KLWX), 43 km from the middle of the area, began a volume at 22:39 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 35 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 533 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 473 m²/s²
0-3 km storm-relative helicity: 699 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.

506 
ACUS11 KWNS 162238
SWOMCD
SPC MCD 162238 
NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-170015-

MESOSCALE DISCUSSION 0461
NWS STORM PREDICTION CENTER NORMAN OK
0538 PM CDT SAT APR 16 2011

AREAS AFFECTED...DC...MD...NRN VA...ERN WV...DE...SWRN NJ...SRN PA

CONCERNING...TORNADO WATCH 151...152...

VALID 162238Z - 170015Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 151...152...CONTINUES.

LATEST SFC MESOANALYSIS DEPICTS LOW PRESSURE OVER NWRN VA WITH A
PREFRONTAL TROUGH TRAILING SWD FROM THE LOW ACROSS THE WRN PERIPHERY
OF WW 151. EAST OF THIS FEATURE...THE MOIST/UNSTABLE SECTOR IS SOUTH
OF A BAROCLINIC ZONE ARCING NEWD FROM THE SFC LOW TOWARD 30 S MRB
AND THEN SEWD TOWARD CHESAPEAKE BAY. SOUTH OF THIS
BOUNDARY...DEWPOINTS IN THE LOWER TO MIDDLE 60S ARE FOUND OVER CNTRL
VA SUPPORTING A WEAKLY UNSTABLE AIR MASS /MLCAPE VALUES OF 250 TO
AROUND 500 J PER KG/. NORTH OF THE BOUNDARY...INSTABILITY IS EVEN
MORE MARGINAL GIVEN SFC DEWPOINTS IN THE MIDDLE 50S.

PERSISTENT SHOWER AND TSTM ACTIVITY IS REINFORCING THE COOL AIR
NORTH OF THE BOUNDARY TO SOME EXTENT. HOWEVER...STRONG ASCENT OVER
THE MID ATLANTIC...REFLECTED BY SFC PRESSURE FALLS OF 4 TO 6 MB PER
2 HRS OVER SERN PA...WILL ALLOW THE SFC LOW TO TRANSLATE NEWD OVER
THE NEXT FEW HOURS WITH SFC WINDS GRADUALLY VEERING ACROSS CNTRL/ERN
VA INTO ERN MD AND SERN PA IN RESPONSE TO ISALLOBARIC FORCING. IN
TURN...MOISTURE TRAJECTORIES WILL BECOME MORE FAVORABLE IN THIS AREA
FOR THE SLIGHTLY HIGHER INSTABILITY /ALBEIT MARGINAL/ AND MORE
ROBUST UPDRAFT POTENTIAL TO NOSE NWD IN TIME. DESPITE THE MARGINAL
DEGREE OF INSTABILITY...STRONG DEEP-LAYER SHEAR /71 KT OF 0-6 KM
SHEAR PER STERLING VWP/ AHEAD OF THE PREFRONTAL TROUGH WILL PROVIDE
ADDITIONAL SUPPORT FOR UPDRAFTS.

THE PRIMARY CONVECTIVE MODE IS FORECAST TO CONSIST OF LINE
SEGMENTS/QLCS STRUCTURES MOVING NEWD...WITH EMBEDDED SUPERCELL
STRUCTURES POSSIBLE OVER SRN PORTIONS OF WW151 INVOF STRONGER
INSTABILITY. VERY STRONG WINDS JUST OFF THE SFC /AROUND 50 KT AT 1
KM PER STERLING VWP/ WILL SUPPORT A DMGG WIND THREAT WITH ANY OF
THIS ACTIVITY. A FEW TORNADOES WILL REMAIN POSSIBLE...AS
WELL...GIVEN THE DEGREE OF LOW-LEVEL SHEAR /EFFECTIVE SRH WELL ABOVE
400 M2 PER S2 IN MANY AREAS/...PARTICULARLY WITH ANY LEWP
STRUCTURES.

..COHEN.. 04/16/2011

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

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

LAT...LON   38227947 39367876 40467829 40947709 40857629 40477550
            39757501 39377492 39027518 38767561 38457576 38227588
            38057603 37967631 38077686 38147722 38057752 37967814
            37707882 37897920 38227947

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 16, 4:41 PM EDT	Tornado Watch	SPC	Kent, New Castle	6 hr
Apr 16, 12:52 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Calvert, Caroline, Charles, Dorchester, Frederick and 10 more	113 min
Apr 16, 1:29 PM EDT	Tornado Watch	SPC	Allegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 8 more	8 hr
Apr 16, 4:29 PM EDT	Mesoscale Discussion	SPC	Allegany, Anne Arundel, Baltimore, Calvert, Carroll, Cecil and 13 more	31 min
Apr 16, 10:43 AM EDT	Mesoscale Discussion	SPC	Fayette, Greene, Washington	62 min
Apr 16, 1:34 PM EDT	Mesoscale Discussion	SPC	Beaver, Crawford, Lawrence, Mercer, Washington	116 min
Apr 16, 2:05 PM EDT	Mesoscale Discussion	SPC	Adams, Bedford, Cumberland, Dauphin, Franklin, Fulton and 6 more	55 min
Apr 16, 10:39 AM EDT	Mesoscale Discussion	SPC	Brunswick, Charles City, Chesterfield, Dinwiddie, Gloucester, Greensville and 25 more	2 hr
Apr 16, 12:02 PM EDT	Tornado Watch PDS	SPC	Amelia, Amherst, Appomattox, Bedford, Brunswick, Buckingham and 62 more	11 hr
Apr 16, 2:28 PM EDT	Mesoscale Discussion	SPC	Amelia, Brunswick, Charles City, Charlotte, Chesterfield, Cumberland and 43 more	92 min
Apr 16, 4:49 PM EDT	Mesoscale Discussion	SPC	Brunswick, Caroline, Charles City, Chesterfield, Dinwiddie, Essex and 33 more	86 min
Apr 16, 6:59 PM EDT	Mesoscale Discussion	SPC	Greensville, Isle of Wight, Prince George, Southampton, Surry, Sussex and 9 more	91 min

Nearby

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