Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 1964

September 18, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Sep 18, 2012, 1:27 PM EDT for 4 states. It was in force for 63 min.

The area

The outline as issued.

The facts

Issued: Sep 18, 2012, 1:27 PM EDT (17:27 UTC)
Expired: Sep 18, 2012, 2:30 PM EDT
In force: 63 min
Issued by: the Storm Prediction Center

All 113 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Dorchester County, MD, Frederick County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Somerset County, MD, Talbot County, MD, Wicomico County, MD, Worcester County, MD, Camden County, NC, Chowan County, NC, Currituck County, NC, Gates County, NC, Hertford County, NC, Northampton County, NC, Pasquotank County, NC, Perquimans County, NC, Accomack County, VA, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Brunswick County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Fairfax, VA, City of Falls Church, VA, City of Franklin, VA, City of Fredericksburg, VA, City of Hampton, VA, City of Hopewell, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Newport News, VA, City of Norfolk, VA, City of Petersburg, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Richmond, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Waynesboro, VA, City of Williamsburg, VA, Clarke County, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Gloucester County, VA, Goochland County, VA, Greene County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Isle of Wight County, VA, James City County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Lancaster County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Mathews County, VA, Mecklenburg County, VA, Middlesex County, VA, Nelson County, VA, New Kent County, VA, Northampton County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Page County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Sussex County, VA, Warren County, VA, Westmoreland County, VA, York County, VA, Jefferson County, WV

The radar

The Norfolk radar (KAKQ), 81 km from the middle of the area, began a volume at 17:28 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, 5.5 hours before the alert went out and 141 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: 371 J/kg
Mixed-layer CIN: 0 J/kg
Mixed-layer LCL: 454 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 322 m²/s²
0-3 km storm-relative helicity: 403 m²/s²
Significant tornado parameter: 0.9
Supercell composite: 4.2

Open this sounding in Storm Lab

The text

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

454 
ACUS11 KWNS 181727
SWOMCD
SPC MCD 181727 
DEZ000-MDZ000-VAZ000-NCZ000-DCZ000-WVZ000-181830-

MESOSCALE DISCUSSION 1964
NWS STORM PREDICTION CENTER NORMAN OK
1227 PM CDT TUE SEP 18 2012

AREAS AFFECTED...CNTRL/ERN VA...CNTRL/ERN MD...WASHINGTON DC...NERN
NC

CONCERNING...TORNADO WATCH 642...

VALID 181727Z - 181830Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 642 CONTINUES.

SUMMARY...THE THREAT FOR DMGG WINDS AND TORNADOES CONTINUES ACROSS
TORNADO WATCH 642.

DISCUSSION...A SQUALL LINE CONTINUES TO CONGEAL FROM S-CNTRL PA SWD
INTO S-CNTRL VA NEAR/EAST OF A SFC CONFLUENCE AXIS. THE LINE WILL
CONTINUE TO ADVANCE EWD ACROSS THE WARM SECTOR LYING OVER THE
PIEDMONT...WHICH IS CHARACTERIZED BY MLCAPE OF AROUND 500-1000 M2/S2
AND RICH DEEP MOISTURE. STRONGLY CURVED/LARGE LOW-LEVEL HODOGRAPHS
PER AREA VWP DATA SUPPORTING EFFECTIVE SRH IN EXCESS OF 300
M2/S2...WITH A 60-KT LOW-LEVEL JET MAX AT 1-KM AGL PER STERLING VWP
DATA...WILL SUPPORT A THREAT FOR WIDESPREAD DMGG WINDS AND
TORNADOES. THE TORNADO THREAT WILL BE HIGHEST WITH EMBEDDED
MESOVORTICES/LEWP STRUCTURES/LINE BREAKS. PRESENT INDICATIONS ARE
THAT THE LINE WOULD REACH THE BALTIMORE/WASHINGTON DC AREA AROUND
THE 1830Z-2030Z TIME-FRAME. ADDITIONAL MORE DISCRETE CONVECTION WITH
SVR WINDS/TORNADOES COULD EVOLVE WITHIN A NWD-SURGE OF WAA-RELATED
PRECIPITATION LEADING THE AFOREMENTIONED SQUALL LINE.

..COHEN.. 09/18/2012

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

ATTN...WFO...PHI...AKQ...LWX...RAH...RNK...

LAT...LON   36037646 36377772 36517868 36557969 37097965 37557934
            38827841 39487781 39657708 39437635 38927601 38477568
            38267491 37517512 36447570 36037646

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 18, 8:49 AM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Carroll, Charles, Frederick and 8 more	116 min
Sep 18, 10:54 AM EDT	Tornado Watch	SPC	Anne Arundel, Baltimore, Calvert, Carroll, Charles, Dorchester and 11 more	9 hr
Sep 18, 11:14 AM EDT	Mesoscale Discussion	SPC	Cecil	91 min
Sep 18, 11:19 AM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 13 more	86 min
Sep 18, 12:10 PM EDT	Tornado Watch	SPC	Caroline, Cecil, Kent, Queen Anne's, Talbot	9 hr
Sep 18, 1:56 PM EDT	Mesoscale Discussion	SPC	Cecil, Harford	64 min
Sep 18, 3:52 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Charles, Dorchester, Howard and 7 more	113 min
Sep 18, 4:21 PM EDT	Mesoscale Discussion	SPC	Caroline, Cecil	114 min
Sep 18, 6:15 PM EDT	Mesoscale Discussion	SPC	Somerset, Wicomico, Worcester	30 min
Sep 17, 8:14 PM EDT	Mesoscale Discussion	SPC	Cherokee, Clay, Graham, Haywood, Henderson, Jackson and 4 more	2 hr
Sep 18, 12:23 AM EDT	Mesoscale Discussion	SPC	Alexander, Buncombe, Burke, Cabarrus, Caldwell, Catawba and 14 more	97 min
Sep 18, 9:45 AM EDT	Tornado Watch	SPC	Alamance, Anson, Chatham, Cumberland, Davidson, Durham and 25 more	8 hr
Sep 18, 11:35 AM EDT	Mesoscale Discussion	SPC	Union	85 min
Sep 18, 1:00 PM EDT	Tornado Watch	SPC	Beaufort, Carteret, Craven, Dare, Duplin, Greene and 9 more	5 hr
Sep 18, 1:21 PM EDT	Mesoscale Discussion	SPC	Alamance, Anson, Chatham, Cumberland, Davidson, Durham and 25 more	84 min
Sep 18, 4:11 PM EDT	Mesoscale Discussion	SPC	Alamance, Anson, Beaufort, Carteret, Chatham, Craven and 40 more	94 min

Nearby

Mesoscale Discussions in Virginia, 2012 Mesoscale Discussions in Maryland, 2012 Mesoscale Discussions in North Carolina, 2012 Every mesoscale discussion in 2012

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.