Alert archive / Virginia / Mesoscale Discussions in 2012

Mesoscale Discussion 1810

August 25, 2012Somerset County, Worcester County, Maryland; 14 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Aug 25, 2012, 11:22 AM EDT for Somerset County, Worcester County, Maryland; 14 counties in Virginia. It was in force for 113 min.

The area

The outline as issued.

The facts

Issued: Aug 25, 2012, 11:22 AM EDT (15:22 UTC)
Expired: Aug 25, 2012, 1:15 PM EDT
In force: 113 min
Issued by: the Storm Prediction Center

Counties Somerset County, MD, Worcester County, MD, Accomack County, VA, City of Hampton, VA, City of Newport News, VA, City of Norfolk, VA, City of Poquoson, VA, City of Portsmouth, VA, Gloucester County, VA, Isle of Wight County, VA, Lancaster County, VA, Mathews County, VA, Middlesex County, VA, Northampton County, VA, Northumberland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 96 km from the middle of the area, began a volume at 15:22 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

Wallops Is Stn, VA (KWAL), launched 12:00Z, 3.4 hours before the alert went out and 82 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: 86 J/kg
Mixed-layer CIN: -59 J/kg
Mixed-layer LCL: 860 m above ground
0-6 km bulk shear: 21 kt
0-1 km storm-relative helicity: -37 m²/s²
0-3 km storm-relative helicity: 64 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.

645 
ACUS11 KWNS 251523
SWOMCD
SPC MCD 251522
MDZ000-VAZ000-251715-

MESOSCALE DISCUSSION 1810
NWS STORM PREDICTION CENTER NORMAN OK
1022 AM CDT SAT AUG 25 2012

AREAS AFFECTED...SERN VA INTO SRN MD

CONCERNING...OUTLOOK UPGRADE

VALID 251522Z - 251715Z

SUMMARY...AT LEAST A MODEST THREAT FOR ISOLATED BRIEF TORNADOES IS
EXPECTED TO PERSIST INTO THE AFTERNOON OVER A SMALL PORTION OF SERN
VA. THREAT AREA MAY SLOWLY BUT GRADUALLY SPREAD NWD INTO SRN MD.
AREA IS BEING EVALUATED AND A SMALL SLIGHT RISK AREA WILL LIKELY BE
INTRODUCED ON THE 1630Z UPDATE.

DISCUSSION...LATE THIS MORNING A SFC LOW WAS LOCATED OVER NERN NC
WITH A WARM OR QUASI-STATIONARY FRONT EXTENDING NEWD FROM THE LOW
INTO EXTREME SERN VA. COLD FRONT STRETCHES SWD THROUGH ERN NC. THE
SFC LOW HAS DEVELOPED IN ASSOCIATION WITH A VERY SLOW MOVING UPPER
LOW CIRCULATION OVER SERN VA. VISIBLE IMAGERY INDICATES THE WARM
SECTOR HAS CLEARED OUT FROM ERN NC INTO SERN VA WHERE DIABATIC
WARMING SHOULD BOOST MLCAPE TO 400-800 J/KG. HOWEVER...A MID-UPPER
LEVEL DRY SLOT INDICATED ON WV IS SHIFTING NWD WHICH MIGHT LIMIT
OVERALL DEEP CONVECTIVE POTENTIAL WITH SWD EXTENT IN WARM SECTOR.
STORMS SHOULD CONTINUE DEVELOPING PRIMARILY ALONG AND JUST NORTH OF
SW-NE ORIENTED WARM FRONT OVER SERN VA WHERE LOW LEVEL WINDS ARE
BACKED TO ELY WITH SUFFICIENT SFC-2 KM VEERING FOR 150-200 M2/S2
STORM RELATIVE HELICITY. THREAT FOR BRIEF ISOLATED TORNADOES MAY
EXIST AS STORMS INTERACT WITH BOUNDARY AND BEFORE WEAKENING AS THEY
CROSS INTO THE COOL SECTOR. MORE ROBUST SEVERE THREAT WILL PROBABLY
REMAIN SOMEWHAT LIMITED BY THE MARGINAL THERMODYNAMIC ENVIRONMENT.

HEAVY RAIN WITH RATES LOCALLY EXCEEDING 2 INCHES PER HOUR IS ALSO
LIKELY FROM SERN AND ERN VA INTO SRN MD NEXT FEW HOURS.

..DIAL/WEISS.. 08/25/2012

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

ATTN...WFO...AKQ...

LAT...LON   37097587 36637684 37897655 38327516 37097587

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 25, 4:46 PM EDT	Mesoscale Discussion	SPC	Somerset, Wicomico, Worcester	89 min
Aug 25, 6:12 AM EDT	Mesoscale Discussion	SPC	Accomack, Gloucester, Isle of Wight, James City, Mathews, Middlesex and 15 more	3 hr

Nearby

Mesoscale Discussions in Virginia, 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.