Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 816

May 15, 20127 counties in Maryland; 27 counties in North Carolina; 106 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at May 15, 2012, 2:08 PM EDT for 7 counties in Maryland; 27 counties in North Carolina; 106 counties in Virginia. It was in force for 67 min.

The area

The outline as issued.

The facts

Issued: May 15, 2012, 2:08 PM EDT (18:08 UTC)
Expired: May 15, 2012, 3:15 PM EDT
In force: 67 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 140 counties

Anne Arundel County, MD, Calvert County, MD, Charles County, MD, Dorchester County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Alamance County, NC, Alexander County, NC, Alleghany County, NC, Burke County, NC, Caldwell County, NC, Caswell County, NC, Catawba County, NC, Davidson County, NC, Davie County, NC, Durham County, NC, Forsyth County, NC, Granville County, NC, Guilford County, NC, Iredell County, NC, McDowell County, NC, Northampton County, NC, Orange County, NC, Person County, NC, Rockingham County, NC, Rowan County, NC, Stokes County, NC, Surry County, NC, Vance County, NC, Warren County, NC, Watauga County, NC, Wilkes County, NC, Yadkin County, NC, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Augusta County, VA, Bedford County, VA, Botetourt County, VA, Brunswick County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Carroll County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Buena Vista, 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 Galax, VA, City of Hampton, VA, City of Harrisonburg, VA, City of Hopewell, VA, City of Lexington, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Newport News, VA, City of Norfolk, VA, City of Petersburg, VA, City of Poquoson, VA, City of Portsmouth, VA, City of Radford, VA, City of Richmond, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Suffolk, 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, Floyd County, VA, Fluvanna County, VA, Franklin County, VA, Gloucester County, VA, Goochland County, VA, Grayson County, VA, Greene County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Henry 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, Montgomery County, VA, Nelson County, VA, New Kent County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Page County, VA, Patrick 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, Roanoke County, VA, Rockbridge 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

The radar

The Roanoke radar (KFCX), 71 km from the middle of the area, began a volume at 18:09 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 279May 15, 3:15 PM EDT

The nearest sounding before it

Roanoke, VA (KRNK), launched 12:00Z, 6.1 hours before the alert went out and 31 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: 54 J/kg
Mixed-layer CIN: -43 J/kg
Mixed-layer LCL: 511 m above ground
0-6 km bulk shear: 27 kt
0-1 km storm-relative helicity: 32 m²/s²
0-3 km storm-relative helicity: 39 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.

290 
ACUS11 KWNS 151809
SWOMCD
SPC MCD 151808
MDZ000-VAZ000-NCZ000-DCZ000-WVZ000-151915-

MESOSCALE DISCUSSION 0816
NWS STORM PREDICTION CENTER NORMAN OK
0108 PM CDT TUE MAY 15 2012

AREAS AFFECTED...WRN NC / WRN-CNTRL-NRN VA / PARTS OF MD

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 151808Z - 151915Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...SCTD TSTMS ARE EXPECTED TO DEVELOP 18-21Z.  THE STRONGER
STORMS WILL POSE AN ISOLD DMGG WIND/LARGE HAIL RISK.

DISCUSSION...SURFACE MESOANALYSIS PLACES A WEAK SURFACE TROUGH
EXTENDING NEWD FROM THE LEE OF THE SRN APPALACHIANS NEWD INTO WRN
VA.  THE INFLUENCE OF WEAK SHORTWAVE RIDGING ALOFT WILL ABATE THIS
AFTERNOON AS A WEAK SHORTWAVE TROUGH OVER THE TN VALLEY MOVES NEWD
WITHIN A BROAD CYCLONIC FLOW REGIME CENTERED FARTHER W OVER THE
LOWER MS RIVER VALLEY.  ALTHOUGH MID-LEVEL LAPSE RATES ARE NOT
PARTICULARLY STEEP /6.5 DEG C PER KM --REF 12Z GSO RAOB/...FURTHER
HEATING WILL ALLOW TEMPS TO CONTINUE TO WARM THROUGH THE 70S AND
INTO THE 80S AND LEAD TO MLCAPE ON THE ORDER OF 1000-1500 J/KG.  AS
SUCH...POCKETS OF SUNSHINE WILL INCREASE 0-2 KM LAPSE RATES AND
BECOME MORE CONDUCIVE FOR INTERMITTENT BOUTS OF STRONGER DOWNDRAFT
PENETRATION IN THE FORM OF LOCALIZED STRONG/MARGINALLY SEVERE WIND
GUSTS.

THE LAST FEW RUNS OF THE HRRR AND OTHER CONVECTION-ALLOWING MODEL
GUIDANCE SHOW SCTD STORMS DEVELOPING IN THE 18-21Z
PERIOD...CONCENTRATED INVOF THE MTNS OVER WRN NC NEWD INTO THE VA
PIEDMONT.  THE MULTICELLULAR CHARACTER OF THESE STORMS SUGGEST AT
LEAST SOME LARGE HAIL RISK WILL DEVELOP WITH THE STRONGER
UPDRAFTS...BEFORE APPRECIABLE CONVECTIVE OVERTURNING/LOSS OF HEATING
TOWARDS EVENING LESSENS THIS RISK.

..SMITH/HART.. 05/15/2012

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

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

LAT...LON   35718220 36248175 39267789 39177670 38487601 36667625
            35608063 35498170 35718220

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 15, 1:07 PM EDT	Mesoscale Discussion	SPC	Anson, Bladen, Brunswick, Columbus, Cumberland, Hoke and 6 more	113 min
May 15, 2:27 PM EDT	Severe Thunderstorm Watch	SPC	Bladen, Brunswick, Columbus, New Hanover, Pender, Robeson	7 hr
May 15, 3:13 PM EDT	Severe Thunderstorm Watch	SPC	Alamance, Alexander, Anson, Buncombe, Burke, Cabarrus and 44 more	7 hr
May 15, 6:30 PM EDT	Mesoscale Discussion	SPC	Alamance, Alexander, Anson, Bladen, Brunswick, Burke and 47 more	90 min

Nearby

Mesoscale Discussions in Virginia, 2012 Mesoscale Discussions in North Carolina, 2012 Mesoscale Discussions in Maryland, 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.