Alert archive / Virginia / Mesoscale Discussions in 2009

Mesoscale Discussion 537

April 20, 200917 counties in North Carolina; 38 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2009, 2:09 PM EDT for 17 counties in North Carolina; 38 counties in Virginia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Apr 20, 2009, 2:09 PM EDT (18:09 UTC)
Expired
Apr 20, 2009, 4:15 PM EDT
In force
2 hr
Issued by
the Storm Prediction Center
All 55 counties

Alamance County, NC, Caswell County, NC, Durham County, NC, Edgecombe County, NC, Franklin County, NC, Granville County, NC, Halifax County, NC, Hertford County, NC, Johnston County, NC, Nash County, NC, Northampton County, NC, Orange County, NC, Person County, NC, Vance County, NC, Wake County, NC, Warren County, NC, Wilson County, NC, Amelia County, VA, Appomattox 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 Colonial Heights, VA, City of Danville, VA, City of Emporia, VA, City of Franklin, VA, City of Hopewell, VA, City of Petersburg, VA, City of Richmond, VA, City of Williamsburg, VA, Cumberland County, VA, Dinwiddie County, VA, Goochland County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Isle of Wight County, VA, James City County, VA, King and Queen County, VA, King William County, VA, Lunenburg County, VA, Mecklenburg County, VA, New Kent County, VA, Nottoway County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA

The radar

The Norfolk radar (KAKQ), 99 km from the middle of the area, began a volume at 18:12 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

Roanoke, VA (KRNK), launched 12:00Z, 6.2 hours before the alert went out and 131 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, Roanoke, VA at 12:00Z on 2009-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 23 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, Roanoke, VA at 12:00Z on 2009-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 185 square meters per square second.1939587897Sfc1 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
23 J/kg
Mixed-layer CIN
-38 J/kg
Mixed-layer LCL
526 m above ground
0-6 km bulk shear
59 kt
0-1 km storm-relative helicity
185 m²/s²
0-3 km storm-relative helicity
217 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, 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, 2:50 PM EDTTornado WatchSPCAlamance, Bertie, Camden, Caswell, Chatham, Chowan and 18 more7 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, 4:57 PM EDTMesoscale DiscussionSPCAlamance, Camden, Caswell, Chatham, Chowan, Durham and 13 more93 min
Apr 20, 7:15 PM EDTMesoscale DiscussionSPCGates, Halifax, Hertford, Northampton, Warren90 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, 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.