Alert archive / Virginia / Mesoscale Discussions in 2008

Mesoscale Discussion 950

May 20, 20085 counties in North Carolina; 43 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at May 20, 2008, 12:34 PM EDT for 5 counties in North Carolina; 43 counties in Virginia. It was in force for 56 min.

The area

The outline as issued.

The facts

Issued: May 20, 2008, 12:34 PM EDT (16:34 UTC)
Expired: May 20, 2008, 1:30 PM EDT
In force: 56 min
Issued by: the Storm Prediction Center

All 48 counties

Caswell County, NC, Northampton County, NC, Person County, NC, Vance County, NC, Warren County, NC, Amelia County, VA, Appomattox County, VA, Brunswick County, VA, Campbell County, VA, Caroline County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Hopewell, VA, City of Martinsville, VA, City of Petersburg, VA, City of Richmond, VA, City of Williamsburg, VA, Cumberland County, VA, Dinwiddie County, VA, Floyd County, VA, Franklin County, VA, Gloucester County, VA, Goochland County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Henry County, VA, James City County, VA, King and Queen County, VA, King William County, VA, Lunenburg County, VA, Mecklenburg County, VA, Middlesex County, VA, New Kent County, VA, Nottoway County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA

The radar

The Roanoke radar (KFCX), 138 km from the middle of the area, began a volume at 16:35 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 327May 20, 1:10 PM EDT

The nearest sounding before it

Roanoke, VA (KRNK), launched 12:00Z, 4.6 hours before the alert went out and 70 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: 781 m above ground
0-6 km bulk shear: 63 kt
0-1 km storm-relative helicity: 399 m²/s²
0-3 km storm-relative helicity: 426 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.

000 
ACUS11 KWNS 201634
SWOMCD
SPC MCD 201634 
VAZ000-NCZ000-201730-

MESOSCALE DISCUSSION 0950
NWS STORM PREDICTION CENTER NORMAN OK
1134 AM CDT TUE MAY 20 2008

AREAS AFFECTED...SERN VA/NRN NC

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

VALID 201634Z - 201730Z

...WATCH WILL BE NEEDED BY 18Z...

SHOWERS ARE DEEPENING OVER THE MOUNTAINS OF WRN VA FROM FLOYD COUNTY
TO SMYTH COUNTY WHERE LIGHTNING IS NOW BEING OBSERVED WITH THE
STRONGEST UPDRAFT.  ADDITIONALLY...SHOWERS ARE NOW SPREADING OFF THE
HIGHER TERRAIN AS BOUNDARY LAYER LAPSE RATES STEEPEN.  LATEST
DIAGNOSTIC DATA INDICATES SFC-3KM VALUES ARE AOA 7 C/KM...INDICATIVE
OF INCREASING BUOYANCY ACROSS THIS REGION.  AS TEMPERATURES CONTINUE
TO RISE THROUGH THE 70S UPSTREAM CONVECTION WILL GRADUALLY BECOME
MORE ROBUST AND THE THREAT OF SEVERE WILL INCREASE MARKEDLY.  GIVEN
THE STRONG WLY VERTICAL SHEAR IT SEEMS POSSIBLE THAT INITIAL STORM
MODE MAY BE DISCRETE SUPERCELL STRUCTURES....ALTHOUGH BOW-TYPE
ECHOES COULD EVOLVE WHICH WOULD POSE A DAMAGING WIND POTENTIAL.

..DARROW.. 05/20/2008

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

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

36978035 37367886 38107751 37657631 36337719 36418047

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 20, 1:09 PM EDT	Severe Thunderstorm Watch	SPC	Alamance, Alexander, Alleghany, Anson, Bertie, Burke and 54 more	7 hr
May 20, 2:59 PM EDT	Severe Thunderstorm Watch	SPC	Avery, Buncombe, Cherokee, Clay, Graham, Haywood and 11 more	7 hr
May 20, 3:23 PM EDT	Mesoscale Discussion	SPC	Bladen, Brunswick, Columbus, Craven, Duplin, Greene and 7 more	37 min
May 20, 3:39 PM EDT	Tornado Watch	SPC	Beaufort, Bladen, Brunswick, Carteret, Columbus, Craven and 15 more	7 hr
May 20, 4:38 PM EDT	Mesoscale Discussion	SPC	Alamance, Bertie, Cabarrus, Camden, Chatham, Chowan and 22 more	67 min
May 20, 7:19 PM EDT	Mesoscale Discussion	SPC	Anson, Hoke, Richmond, Scotland, Union	86 min

Nearby

Mesoscale Discussions in Virginia, 2008 Mesoscale Discussions in North Carolina, 2008 Every mesoscale discussion in 2008

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.