Alert archive / Virginia / Mesoscale Discussions in 2009

Mesoscale Discussion 541

April 20, 2009Saint Mary's County, Maryland; 5 counties in North Carolina; 47 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2009, 7:15 PM EDT for Saint Mary's County, Maryland; 5 counties in North Carolina; 47 counties in Virginia. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued
Apr 20, 2009, 7:15 PM EDT (23:15 UTC)
Expired
Apr 20, 2009, 8:45 PM EDT
In force
90 min
Issued by
the Storm Prediction Center
All 53 counties

Saint Mary's County, MD, Gates County, NC, Halifax County, NC, Hertford County, NC, Northampton County, NC, Warren County, NC, Amelia County, VA, Brunswick County, VA, Caroline County, VA, Charles City County, VA, Chesterfield County, VA, City of Chesapeake, VA, City of Colonial Heights, VA, City of Emporia, VA, City of Franklin, VA, City of Hampton, VA, City of Hopewell, 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 Suffolk, VA, City of Williamsburg, VA, Dinwiddie County, VA, Essex County, VA, Gloucester County, VA, Goochland County, VA, Greensville County, VA, Hanover County, VA, Henrico 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, Mathews County, VA, Middlesex County, VA, New Kent County, VA, Northumberland County, VA, Nottoway County, VA, Powhatan County, VA, Prince George County, VA, Richmond County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 26 km from the middle of the area, began a volume at 23:17 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, 11.3 hours before the alert went out and 194 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, Wallops Is Stn, VA at 12:00Z on 2009-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 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, Wallops Is Stn, VA at 12:00Z on 2009-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 103 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
766 m above ground
0-6 km bulk shear
46 kt
0-1 km storm-relative helicity
103 m²/s²
0-3 km storm-relative helicity
270 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.

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SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 20, 2:50 PM EDTTornado WatchSPCCalvert, Charles, Saint Mary's7 hr
Apr 20, 4:57 PM EDTMesoscale DiscussionSPCCharles, Saint Mary's, Somerset93 min
Apr 20, 12:42 AM EDTTornado WatchSPCCatawba, Cleveland, Gaston, Henderson, Lincoln, Mecklenburg and 2 more5 hr
Apr 20, 12:22 PM EDTMesoscale DiscussionSPCBeaufort, Bertie, Camden, Chowan, Craven, Edgecombe and 19 more83 min
Apr 20, 2:09 PM EDTMesoscale DiscussionSPCAlamance, Caswell, Durham, Edgecombe, Franklin, Granville and 11 more2 hr
Apr 20, 2:52 PM EDTMesoscale DiscussionSPCBladen, Brunswick, Columbus, Duplin, New Hanover, Pender83 min
Apr 20, 3:16 PM EDTSevere Thunderstorm WatchSPCBeaufort, Bladen, Brunswick, Carteret, Columbus, Craven and 25 more6 hr
Apr 20, 4:55 PM EDTMesoscale DiscussionSPCBeaufort, Bertie, Bladen, Brunswick, Carteret, Chowan and 20 more95 min
Apr 20, 7:36 PM EDTMesoscale DiscussionSPCBeaufort, Bladen, Columbus, Craven, Duplin, Greene and 12 more84 min

Nearby

Mesoscale Discussions in Virginia, 2009Mesoscale Discussions in North Carolina, 2009Mesoscale Discussions in Maryland, 2009Every mesoscale discussion in 2009

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.