Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 1321

June 30, 20125 states

The Storm Prediction Center issued this mesoscale discussion at Jun 30, 2012, 4:27 PM EDT for 5 states. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Jun 30, 2012, 4:27 PM EDT (20:27 UTC)
Expired: Jun 30, 2012, 7:00 PM EDT
In force: 3 hr
Issued by: the Storm Prediction Center
Chance of a watch: 80%

All 101 counties

Montgomery County, MD, Alleghany County, NC, Ashe County, NC, Caswell County, NC, Forsyth County, NC, Person County, NC, Rockingham County, NC, Stokes County, NC, Surry County, NC, Watauga County, NC, Wilkes County, NC, Yadkin County, NC, Johnson County, TN, Albemarle County, VA, Alleghany County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Augusta County, VA, Bath County, VA, Bedford County, VA, Bland County, VA, Botetourt County, VA, Buchanan County, VA, Buckingham County, VA, Campbell County, VA, Carroll County, VA, Charlotte County, VA, City of Alexandria, VA, City of Bristol, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Covington, VA, City of Danville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Galax, VA, City of Harrisonburg, VA, City of Lexington, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Norton, VA, City of Radford, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Craig County, VA, Culpeper County, VA, Cumberland County, VA, Dickenson County, VA, Fairfax County, VA, Fauquier County, VA, Floyd County, VA, Fluvanna County, VA, Franklin County, VA, Frederick County, VA, Giles County, VA, Goochland County, VA, Grayson County, VA, Greene County, VA, Halifax County, VA, Henry County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Montgomery County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince William County, VA, Pulaski County, VA, Rappahannock County, VA, Roanoke County, VA, Rockbridge County, VA, Rockingham County, VA, Russell County, VA, Shenandoah County, VA, Smyth County, VA, Spotsylvania County, VA, Stafford County, VA, Tazewell County, VA, Warren County, VA, Washington County, VA, Wise County, VA, Wythe County, VA, Jefferson County, WV, McDowell County, WV, Mercer County, WV, Monroe County, WV, Summers County, WV

The radar

The Roanoke radar (KFCX), 78 km from the middle of the area, began a volume at 20:27 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, 8.5 hours before the alert went out and 60 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: 656 J/kg
Mixed-layer CIN: -356 J/kg
Mixed-layer LCL: 1666 m above ground
0-6 km bulk shear: 25 kt
0-1 km storm-relative helicity: -1 m²/s²
0-3 km storm-relative helicity: 47 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.

305 
ACUS11 KWNS 302027
SWOMCD
SPC MCD 302027 
MDZ000-DCZ000-VAZ000-WVZ000-NCZ000-TNZ000-KYZ000-302300-

MESOSCALE DISCUSSION 1321
NWS STORM PREDICTION CENTER NORMAN OK
0327 PM CDT SAT JUN 30 2012

AREAS AFFECTED...CNTRL/SRN APPALACHIANS AND ADJACENT PIEDMONT

CONCERNING...SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY 

VALID 302027Z - 302300Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...ISOLATED TSTMS SHOULD FORM WITHIN A HOT/DEEPLY-MIXED AIR
MASS FROM PARTS OF ERN KY TO WRN VA. ALTHOUGH IT REMAINS UNCLEAR HOW
CONVECTION WILL EVOLVE...POTENTIAL FOR CLUSTERING AMIDST MODERATE TO
STRONG DEEP-LAYER W/NWLYS SHOULD BE SUFFICIENT FOR ISOLATED TO
WIDELY SCATTERED DAMAGING WIND EVENTS THIS EVENING.

DISCUSSION...GROWING CU WAS NOTED FROM ERN KY TO WRN VA IN RECENT
VISIBLE SATELLITE IMAGERY...WITHIN A HOT AIR MASS CHARACTERIZED BY
SURFACE TEMPERATURES IN THE MIDDLE 90S TO AROUND 102. ALTHOUGH
SURFACE DEW POINTS HAVE LARGELY MIXED INTO THE UPPER 50S TO MIDDLE
60S...MODIFIED 18Z IAD RAOB AND PREVIOUS GENERATION RUC VERSION OF
SFCOA WOULD SUPPORT MODERATE BUOYANCY WITH MLCAPE OF 1000-2500 J/KG.
DEEP-LAYER SPEED SHEAR WAS STRONG IN THE 18Z IAD RAOB IN ASSOCIATION
WITH A WEAK IMPULSE PROGRESSING ACROSS ERN PA INTO NJ. ALTHOUGH FLOW
WEAKENS SOMEWHAT WITH SLY EXTENT...IT SHOULD REMAIN SUFFICIENT FOR
ORGANIZED UPDRAFTS. GIVEN THE STEEP LOW-LEVEL LAPSE
RATES...CONGLOMERATION OF COLD POOLS SHOULD FAVOR UPSCALE GROWTH
INTO ONE OR MORE CLUSTERS. PRIMARY RISK WILL LIKELY BE DAMAGING
WINDS.

..GRAMS/THOMPSON/HART.. 06/30/2012

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

ATTN...WFO...AKQ...LWX...RAH...RNK...RLX...MRX...JKL...

LAT...LON   37468258 37508140 37848033 38787896 39437812 39477760
            39317715 39097699 38537707 37067818 36297895 36087998
            36098102 36218174 36568229 36908281 37468258

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jun 29, 10:09 PM EDT	Severe Thunderstorm Watch	SPC	Caroline, Cecil, Dorchester, Kent, Queen Anne's, Somerset and 3 more	4 hr
Jun 29, 10:51 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 14 more	84 min
Jun 30, 7:39 PM EDT	Mesoscale Discussion	SPC	Anne Arundel, Calvert, Caroline, Charles, Dorchester, Kent and 7 more	3 hr

Nearby

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