Alert archive / Virginia / Mesoscale Discussions in 2009

Mesoscale Discussion 1739

July 31, 200921 counties in North Carolina; 33 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Jul 31, 2009, 4:47 PM EDT for 21 counties in North Carolina; 33 counties in Virginia. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued: Jul 31, 2009, 4:47 PM EDT (20:47 UTC)
Expired: Jul 31, 2009, 6:15 PM EDT
In force: 88 min
Issued by: the Storm Prediction Center

All 54 counties

Bertie County, NC, Chowan County, NC, Edgecombe County, NC, Franklin County, NC, Gates County, NC, Granville County, NC, Greene County, NC, Halifax County, NC, Harnett County, NC, Hertford County, NC, Johnston County, NC, Lee County, NC, Martin County, NC, Nash County, NC, Northampton County, NC, Pitt County, NC, Vance County, NC, Wake County, NC, Warren County, NC, Wayne County, NC, Wilson County, NC, Brunswick 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, Gloucester County, VA, Greensville County, VA, Hanover County, VA, Henrico County, VA, Isle of Wight County, VA, James City County, VA, King William County, VA, Mathews County, VA, New Kent County, VA, Northampton County, VA, Prince George County, VA, Southampton County, VA, Surry County, VA, Sussex County, VA, York County, VA

The radar

The Raleigh/Durham radar (KRAX), 75 km from the middle of the area, began a volume at 20:49 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

Roanoke, VA (KRNK), launched 12:00Z, 8.8 hours before the alert went out and 183 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: 271 J/kg
Mixed-layer CIN: -84 J/kg
Mixed-layer LCL: 785 m above ground
0-6 km bulk shear: 49 kt
0-1 km storm-relative helicity: 124 m²/s²
0-3 km storm-relative helicity: 192 m²/s²
Significant tornado parameter: 0.1
Supercell composite: 0.7

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.

Issued	Product	Office	Counties	Lasted
Jul 31, 2:25 PM EDT	Severe Thunderstorm Watch	SPC	Alamance, Anson, Bertie, Camden, Chatham, Chowan and 39 more	6 hr
Jul 31, 6:54 PM EDT	Mesoscale Discussion	SPC	Alamance, Bertie, Chatham, Chowan, Cumberland, Duplin and 24 more	66 min
Jul 31, 12:06 PM EDT	Mesoscale Discussion	SPC	Arlington, Caroline, Essex, Fairfax, Hanover, King and Queen and 19 more	84 min
Jul 31, 1:18 PM EDT	Severe Thunderstorm Watch	SPC	Arlington, Culpeper, Fairfax, Fauquier, King George, Loudoun and 12 more	7 hr
Jul 31, 3:05 PM EDT	Mesoscale Discussion	SPC	Arlington, Culpeper, Fairfax, King George, Prince William, Stafford and 5 more	85 min

Nearby

Mesoscale Discussions in Virginia, 2009 Mesoscale Discussions in North Carolina, 2009 Every 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.