Alert archive / Virginia / Mesoscale Discussions in 2014

Mesoscale Discussion 1663

September 2, 20144 states

The Storm Prediction Center issued this mesoscale discussion at Sep 2, 2014, 4:11 PM EDT for 4 states. It was in force for 94 min.

The area

The outline as issued.

The facts

Issued: Sep 2, 2014, 4:11 PM EDT (20:11 UTC)
Expired: Sep 2, 2014, 5:45 PM EDT
In force: 94 min
Issued by: the Storm Prediction Center
Chance of a watch: 20%

All 80 counties

Allegany County, MD, Baltimore County, MD, Carroll County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Washington County, MD, Adams County, PA, Chester County, PA, Lancaster County, PA, York County, PA, Albemarle County, VA, Alleghany County, VA, Arlington County, VA, Augusta County, VA, Bath County, VA, Botetourt County, VA, City of Alexandria, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Covington, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Harrisonburg, VA, City of Lexington, 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, Craig County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Frederick County, VA, Giles County, VA, Greene County, VA, Highland County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Rockbridge County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Berkeley County, WV, Boone County, WV, Fayette County, WV, Grant County, WV, Greenbrier County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Logan County, WV, McDowell County, WV, Mercer County, WV, Mineral County, WV, Monroe County, WV, Morgan County, WV, Nicholas County, WV, Pendleton County, WV, Pocahontas County, WV, Raleigh County, WV, Randolph County, WV, Summers County, WV, Tucker County, WV, Webster County, WV, Wyoming County, WV

The radar

The Sterling radar (KLWX), 108 km from the middle of the area, began a volume at 20:11 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 489Sep 2, 4:40 PM EDT

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 8.2 hours before the alert went out and 115 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: 497 J/kg
Mixed-layer CIN: -108 J/kg
Mixed-layer LCL: 1408 m above ground
0-6 km bulk shear: 17 kt
0-1 km storm-relative helicity: 68 m²/s²
0-3 km storm-relative helicity: 90 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.

921 
ACUS11 KWNS 022011
SWOMCD
SPC MCD 022011 
PAZ000-MDZ000-DCZ000-VAZ000-WVZ000-KYZ000-022145-

MESOSCALE DISCUSSION 1663
NWS STORM PREDICTION CENTER NORMAN OK
0311 PM CDT TUE SEP 02 2014

AREAS AFFECTED...ERN WV...NRN/WRN VA...MD...SERN PA...WASHINGTON DC

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 022011Z - 022145Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...ISOLATED STRONG TO LOCALLY SVR WIND GUSTS AND OCCASIONAL
INSTANCES OF HAIL WILL BE POSSIBLE THIS AFTERNOON ACROSS THE
MID-ATLANTIC INTO THE CNTRL APPALACHIANS. COVERAGE/MAGNITUDE OF THE
SVR THREAT APPEAR INSUFFICIENT TO WARRANT A WW...BUT TRENDS CONTINUE
TO BE MONITORED.

DISCUSSION...CONVECTIVE TRENDS SUGGEST A SLOW UPTICK IN TSTM
DEVELOPMENT ACROSS THE MID-ATLANTIC INTO THE CNTRL APPALACHIANS THIS
AFTERNOON...INFLUENCED BY LARGE-SCALE ASCENT ACCOMPANYING A
SHORTWAVE TROUGH MOVING THROUGH THE GREAT LAKES AND OH VALLEY. 
SFC OBS FROM 20Z INDICATE GENERALLY WEAK LOW-LEVEL CONVERGENCE
AMIDST NEARLY UNIFORM SWLY FLOW...WITH EXCEPTION TO A MORE
SUBSTANTIAL SLY COMPONENT NOTED OVER NW VA AND CNTRL MD...INVOF A
STRONG TSTM LOCATED NW OF WASHINGTON DC. RICH BOUNDARY LAYER
MOISTURE AMIDST STRONG HEATING /TEMPERATURES IN THE 80S-LOW 90S F/
IS YIELDING MLCAPE VALUES OF 1000-1500 J/KG...AND COMBINED WITH
EFFECTIVE SHEAR VALUES ESTIMATED AT 25-35 KT...THE ENVIRONMENT
REMAINS FAVORABLE FOR ORGANIZED TSTM CLUSTERS AND PERHAPS BRIEFLY
ORGANIZED DISCRETE STRUCTURES TO PERSIST THROUGH LATE AFTERNOON AND
EARLY EVENING. PRIMARY THREAT WILL BE ISOLATED STRONG-SVR WIND
GUSTS...WITH A LESSER THREAT FOR HAIL. COVERAGE/MAGNITUDE OF THESE
THREATS IS CURRENTLY EXPECTED TO REMAIN INSUFFICIENT FOR WW
ISSUANCE...BUT CONVECTIVE TRENDS WILL CONTINUE TO BE MONITORED.

..ROGERS/HART.. 09/02/2014

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

ATTN...WFO...PHI...AKQ...CTP...LWX...RNK...PBZ...RLX...JKL...

LAT...LON   39737809 39927734 40367611 40287590 40007567 39697587
            39067651 37957791 37937805 37517979 37318040 37268165
            37548209 37888208 38178139 38668002 39097972 39637908
            39737809

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 2, 4:39 PM EDT	Severe Thunderstorm Watch	SPC	Anne Arundel, Baltimore, Carroll, Frederick, Harford, Howard and 3 more	5 hr
Sep 2, 6:29 PM EDT	Mesoscale Discussion	SPC	Cecil	91 min
Sep 2, 2:25 PM EDT	Mesoscale Discussion	SPC	Allegheny, Armstrong, Beaver, Bedford, Blair, Bradford and 40 more	2 hr
Sep 2, 7:43 PM EDT	Mesoscale Discussion	SPC	Lackawanna, Wayne	92 min
Sep 2, 4:49 PM EDT	Mesoscale Discussion	SPC	Buchanan, Dickenson, Lee, Scott, Wise, City of Norton	56 min

Nearby

Mesoscale Discussions in Virginia, 2014 Mesoscale Discussions in West Virginia, 2014 Mesoscale Discussions in Maryland, 2014 Every mesoscale discussion in 2014

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.