Alert archive / Virginia / Mesoscale Discussions in 2011

Mesoscale Discussion 796

May 17, 2011Calvert County, Charles County, Saint Mary's County, Maryland; 22 counties in North Carolina; 94 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at May 17, 2011, 11:14 AM EDT for Calvert County, Charles County, Saint Mary's County, Maryland; 22 counties in North Carolina; 94 counties in Virginia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
May 17, 2011, 11:14 AM EDT (15:14 UTC)
Expired
May 17, 2011, 1:15 PM EDT
In force
2 hr
Issued by
the Storm Prediction Center
All 119 counties

Calvert County, MD, Charles County, MD, Saint Mary's County, MD, Bertie County, NC, Camden County, NC, Caswell County, NC, Chowan County, NC, Currituck County, NC, Franklin County, NC, Gates County, NC, Granville County, NC, Halifax County, NC, Hertford County, NC, Hyde County, NC, Martin County, NC, Northampton County, NC, Pasquotank County, NC, Perquimans County, NC, Person County, NC, Rockingham County, NC, Stokes County, NC, Tyrrell County, NC, Vance County, NC, Warren County, NC, Washington County, NC, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Augusta County, VA, Bedford County, VA, Botetourt 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 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 Franklin, VA, City of Fredericksburg, VA, City of Hampton, 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 Richmond, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Suffolk, VA, City of Virginia Beach, VA, City of Waynesboro, VA, City of Williamsburg, 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, 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, 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, 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, Rockbridge County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 65 km from the middle of the area, began a volume at 15:15 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

Roanoke, VA (KRNK), launched 12:00Z, 3.2 hours before the alert went out and 158 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-pSkew-T log-p diagram, Roanoke, VA at 12:00Z on 2011-05-17Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 12 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Roanoke, VA at 12:00Z on 2011-05-17The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 233 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
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
12 J/kg
Mixed-layer CIN
-55 J/kg
Mixed-layer LCL
472 m above ground
0-6 km bulk shear
30 kt
0-1 km storm-relative helicity
233 m²/s²
0-3 km storm-relative helicity
287 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.1

Open this sounding in Storm Lab

The text

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

582 
ACUS11 KWNS 171514
SWOMCD
SPC MCD 171514 
VAZ000-NCZ000-MDZ000-171715-

MESOSCALE DISCUSSION 0796
NWS STORM PREDICTION CENTER NORMAN OK
1014 AM CDT TUE MAY 17 2011

AREAS AFFECTED...PARTS OF CENTRAL/SRN VA...SRN MD AND NRN NC

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 171514Z - 171715Z

STRONGER AND PERSISTENT UPDRAFTS WILL HAVE THE POTENTIAL TO PRODUCE
AN ISOLATED STRONG WIND GUST OR TWO.  GIVEN THE PRESENCE OF AMBIENT
VORTICITY ATTENDANT TO THE CLOSED LOW TRACKING NNWWD FROM CENTRAL NC
AND SURFACE VORTICITY FOCUSED INVOF TWO WARM FRONTS OVER VA...A LOW
PROBABILITY EXISTS FOR AN ISOLATED TORNADO.

LATE MORNING SURFACE ANALYSES SHOWED AN AREA OF LOW PRESSURE
CENTERED OVER WEST CENTRAL NC /40 SSW GSO/ WITH THIS FEATURE MOVING
SLOWLY NWD.  ONE WARM FRONT EXTENDED NNEWD FROM THIS LOW INTO WRN VA
/NEAR SHD/ AND THEN THROUGH SERN PA TO ALONG/S OF LONG ISLAND.  A
SECOND WARM FRONT/DIFFERENTIAL HEATING BOUNDARY /PER VISIBLE IMAGERY
AND SURFACE OBSERVATIONS/ EXTENDED NEWD INTO CENTRAL VA AND THEN
STRETCHED SEWD TO JUST N OF ORF.  SURFACE HEATING ALONG/S OF THE
SECOND WARM FRONT HAS ALLOWED TEMPERATURES TO RISE INTO THE MID 60S
TO AROUND 70...EFFECTIVELY ELIMINATING THE WEAK CAP THAT WAS PRESENT
ON THE 12Z SOUNDINGS AND SUPPORTING CU DEVELOPMENT PER VISIBLE
IMAGERY.  DESPITE THE DIABATIC HEATING...MODEST MIDLEVEL LAPSE RATES
/6-6.5 C PER KM/ ARE TENDING TO INHIBIT STRONGER DESTABILIZATION. 
ADDITIONAL SURFACE HEATING WILL...HOWEVER...STEEPEN LOW LEVEL LAPSE
RATES AND ENHANCE THE POTENTIAL FOR STRONGER WIND GUSTS WITH MORE
PERSISTENT STORMS TODAY.  

AT 15Z...REGIONAL RADAR IMAGERY SHOWED A PERSISTENT AREA OF TSTMS
MOVING NWD ACROSS CENTRAL VA WITH THIS ACTIVITY LOCATED ALONG THE
SECONDARY WARM FRONT/LOW LEVEL CONVERGENCE.  TSTMS WERE ALSO
TRACKING NWD THROUGH NERN NC WITH THIS ACTIVITY LIKELY ATTENDANT TO
STRONGER DCVA WITH A MIDLEVEL IMPULSE ROTATING THROUGH THE NERN
PERIPHERY OF THE NC CLOSED LOW.  ALTHOUGH DEEP LAYER SHEAR WILL
INCREASE AS STRONGER MIDLEVEL WINDS SPREAD ACROSS VA/NRN NC
SUPPORTING PRIMARILY MULTICELLS...WEAK INSTABILITY IS EXPECTED TO
PRECLUDE GREATER COVERAGE OF STRONGER STORMS.  THESE FACTORS SUGGEST
A WW IS NOT WARRANTED AT THIS TIME.

..PETERS.. 05/17/2011

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

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

LAT...LON   35147612 35957762 36187967 36248036 36738061 38117936
            38717844 38917760 38697667 38357631 37607579 36277581
            35147612

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 17, 6:27 PM EDTMesoscale DiscussionSPCAnne Arundel, Baltimore, Caroline, Carroll, Cecil, Frederick and 9 more2 hr
May 17, 6:51 PM EDTMesoscale DiscussionSPCBladen, Columbus, Robeson, Scotland114 min

Nearby

Mesoscale Discussions in Virginia, 2011Mesoscale Discussions in North Carolina, 2011Mesoscale Discussions in Maryland, 2011Every 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.