Alert archive / Virginia / Mesoscale Discussions in 2011

Mesoscale Discussion 641

April 27, 201114 counties in Maryland; 6 counties in North Carolina; 60 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 27, 2011, 7:55 PM EDT for 14 counties in Maryland; 6 counties in North Carolina; 60 counties in Virginia. It was in force for 65 min.

The area

The outline as issued.

The facts

Issued
Apr 27, 2011, 7:55 PM EDT (23:55 UTC)
Expired
Apr 27, 2011, 9:00 PM EDT
In force
65 min
Issued by
the Storm Prediction Center
All 80 counties

Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Saint Mary's County, MD, Talbot County, MD, Alamance County, NC, Caswell County, NC, Granville County, NC, Orange County, NC, Person County, NC, Rockingham County, NC, Albemarle County, VA, Amelia County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Bedford 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 Alexandria, VA, City of Charlottesville, VA, City of Colonial Heights, VA, City of Danville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Hopewell, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Martinsville, VA, City of Petersburg, VA, City of Richmond, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Goochland County, VA, Greene County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, King and Queen County, VA, King George County, VA, King William County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Mecklenburg County, VA, Nelson County, VA, New Kent County, VA, Nottoway County, VA, Orange County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA

The radar

The Norfolk radar (KAKQ), 108 km from the middle of the area, began a volume at 23:55 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.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 11.9 hours before the alert went out and 129 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, Washington/Dulle, VA at 12:00Z on 2011-04-27Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 215 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, Washington/Dulle, VA at 12:00Z on 2011-04-27The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 123 square meters per square second.193958Sfc1 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
215 J/kg
Mixed-layer CIN
-75 J/kg
Mixed-layer LCL
636 m above ground
0-6 km bulk shear
39 kt
0-1 km storm-relative helicity
123 m²/s²
0-3 km storm-relative helicity
150 m²/s²
Significant tornado parameter
0.1
Supercell composite
0.8

Open this sounding in Storm Lab

The text

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

010 
ACUS11 KWNS 272355
SWOMCD
SPC MCD 272355 
MDZ000-PAZ000-VAZ000-DCZ000-NCZ000-280100-

MESOSCALE DISCUSSION 0641
NWS STORM PREDICTION CENTER NORMAN OK
0655 PM CDT WED APR 27 2011

AREAS AFFECTED...CNTRL/ERN MD...CNTRL VA...N-CNTRL NC

CONCERNING...TORNADO WATCH 240...

VALID 272355Z - 280100Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 240 CONTINUES.

TORNADO THREAT CONTINUES WITHIN WW 240 AS NUMEROUS DISCRETE
STORMS...MANY OF WHICH ARE EXHIBITING ROTATION AND SPLITTING
SUPERCELL CHARACTERISTICS...PERSIST WITHIN A BROAD WARM SECTOR FROM
CNTRL MD SWWD TO N-CNTRL NC. AREA VWP DATA HAS SHOWN STRENGTHENING
OF LOW-LEVEL FLOW DURING THE PAST HOUR WITH 0-1 KM SHEAR OF 30-40 KT
BECOMING INCREASINGLY COMMON. LEAD UPPER-LEVEL IMPULSE /EVIDENT IN
WATER VAPOR IMAGERY/ SHIFTING NE ACROSS THE MID-ATLANTIC SHOULD
SERVE TO MAINTAIN FORCED ASCENT AND TSTM ACTIVITY THROUGH MUCH OF
THE EVENING. SUBSIDENCE IN THE WAKE OF THIS IMPULSE SHOULD MITIGATE
ADDITIONAL DEVELOPMENT S OF ONGOING TSTMS IN N-CNTRL NC.

..GRAMS.. 04/27/2011

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

ATTN...WFO...PHI...AKQ...CTP...LWX...RAH...RNK...

LAT...LON   36577817 35937912 36298011 37367953 39037798 39787676
            39667615 39147597 38587606 37827649 36937754 36577817

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 27, 1:23 PM EDTTornado WatchSPCAllegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 8 more5 hr
Apr 27, 1:24 PM EDTMesoscale DiscussionSPCAllegany, Garrett96 min
Apr 27, 3:10 PM EDTTornado WatchSPCGarrett7 hr
Apr 27, 3:55 PM EDTMesoscale DiscussionSPCCaroline, Cecil, Dorchester, Harford, Kent, Queen Anne's and 3 more65 min
Apr 27, 4:39 PM EDTMesoscale DiscussionSPCAllegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 10 more66 min
Apr 27, 6:00 PM EDTMesoscale DiscussionSPCAnne Arundel, Baltimore, Calvert, Carroll, Charles, Frederick and 9 more60 min
Apr 27, 6:15 PM EDTTornado WatchSPCAllegany, Anne Arundel, Baltimore, Calvert, Carroll, Charles and 8 more6 hr
Apr 27, 6:50 PM EDTMesoscale DiscussionSPCCarroll, Harford, Washington55 min
Apr 27, 8:34 AM EDTTornado WatchSPCCherokee, Clay4 hr
Apr 27, 11:27 AM EDTTornado WatchSPCCherokee, Clay6 hr
Apr 27, 12:39 PM EDTMesoscale DiscussionSPCCherokee66 min
Apr 27, 12:51 PM EDTMesoscale DiscussionSPCAlamance, Anson, Bertie, Bladen, Cabarrus, Caswell and 47 more84 min
Apr 27, 2:03 PM EDTMesoscale DiscussionSPCCherokee, Clay, Graham57 min
Apr 27, 3:22 PM EDTMesoscale DiscussionSPCAlleghany, Ashe, Avery, Buncombe, Caldwell, Haywood and 6 more83 min
Apr 27, 4:36 PM EDTTornado Watch PDSSPCCherokee, Clay8 hr
Apr 27, 6:41 PM EDTMesoscale DiscussionSPCAlexander, Avery, Buncombe, Burke, Caldwell, Catawba and 16 more34 min
Apr 27, 6:52 PM EDTTornado Watch PDSSPCAlexander, Avery, Buncombe, Burke, Caldwell, Catawba and 19 more9 hr
Apr 27, 5:38 PM EDTMesoscale DiscussionSPCBuchanan, Dickenson, Lee, Russell, Scott, Wise and 1 more37 min
Apr 27, 5:44 PM EDTTornado WatchSPCBuchanan, Dickenson, Lee, Russell, Scott, Smyth and 5 more7 hr

Nearby

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