Alert archive / Virginia / Mesoscale Discussions in 2011

Mesoscale Discussion 2255

October 13, 20119 counties in Maryland; 28 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Oct 13, 2011, 6:53 PM EDT for 9 counties in Maryland; 28 counties in Virginia. It was in force for 97 min.

The area

The outline as issued.

The facts

Issued: Oct 13, 2011, 6:53 PM EDT (22:53 UTC)
Expired: Oct 13, 2011, 8:30 PM EDT
In force: 97 min
Issued by: the Storm Prediction Center

All 37 counties

Anne Arundel County, MD, Calvert County, MD, Charles County, MD, Dorchester County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Talbot County, MD, Arlington County, VA, Caroline County, VA, City of Alexandria, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Manassas, VA, City of Manassas Park, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Gloucester County, VA, Hanover 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, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northumberland County, VA, Prince William County, VA, Richmond County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA

The radar

The Sterling radar (KLWX), 84 km from the middle of the area, began a volume at 22:54 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

Washington/Dulle, VA (KIAD), launched 12:00Z, 10.9 hours before the alert went out and 78 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: 69 J/kg
Mixed-layer CIN: -167 J/kg
Mixed-layer LCL: 451 m above ground
0-6 km bulk shear: 36 kt
0-1 km storm-relative helicity: 115 m²/s²
0-3 km storm-relative helicity: 180 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.

772 
ACUS11 KWNS 132253
SWOMCD
SPC MCD 132253 
VAZ000-MDZ000-DCZ000-140030-

MESOSCALE DISCUSSION 2255
NWS STORM PREDICTION CENTER NORMAN OK
0553 PM CDT THU OCT 13 2011

AREAS AFFECTED...ERN VA AND WRN AND NRN MD

CONCERNING...TORNADO WATCH 866...

VALID 132253Z - 140030Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 866 CONTINUES.

THE THREAT FOR ISOLATED TORNADOES AND ISOLATED DAMAGING WIND SHOULD
PERSIST THROUGH EARLY EVENING MAINLY ACROSS NERN VA THROUGH WRN AND
NRN MD. HOWEVER...OVERALL THREAT SHOULD BEGIN A GRADUAL DECREASE BY
01Z.

EARLY THIS EVENING A WARM FRONT EXTENDS FROM CNTRL MD THROUGH NRN VA
AND WNWWD INTO THE OH VALLEY. MOIST WARM SECTOR PERSIST SOUTH OF THE
FRONT WITH UPPER 60S-70F DEWPOINTS. HOWEVER...INSTABILITY REMAINS
MARGINAL OWING TO MODEST LAPSE RATES PROFILES. STORMS WILL CONTINUE
DEVELOPING WITHIN WEAKLY CAPPED WARM SECTOR AND IN ASSOCIATION WITH
VORT MAX EJECTING NWD THROUGH VA THIS EVENING. VWP DATA INDICATE
35-40 KT 0-6 KM SHEAR OVER THE MID ATLANTIC...AND LOW LEVEL
HODOGRAPHS ARE MAXIMIZED NEAR THE WARM FRONT WHERE THE FLOW IS
BACKED TO SELY WITH 0-1 KM STORM RELATIVE HELICITY FROM 100-200
M2/S2. SOME FURTHER INCREASE IN LOW LEVEL SHEAR MAY OCCUR DURING THE
NEXT COUPLE HOURS AS THE LLJ STRENGTHENS. ISOLATED TORNADOES REMAIN
POSSIBLE ANYWHERE WITHIN THE WATCH AREA...BUT THE GREATEST TORNADO
THREAT APPEARS TO BE ACROSS NERN VA INTO NRN AND WRN MD AS STORMS
LIFT NWD AND INTERACT WITH THE BOUNDARY. OVERALL THREAT SHOULD BEGIN
A GRADUAL DECREASE BY 01Z AS THE BOUNDARY LAYER COOLS AND
STABILIZES.

..DIAL.. 10/13/2011

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

ATTN...WFO...PHI...AKQ...LWX...

LAT...LON   38937800 39407702 39157618 38317593 37447608 37297672
            37547742 37897772 38937800

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Oct 13, 4:28 PM EDT	Tornado Watch	SPC	Anne Arundel, Baltimore, Calvert, Charles, Dorchester, Harford and 5 more	4 hr

Nearby

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