Alert archive / Virginia / Mesoscale Discussions in 2008

Mesoscale Discussion 751

April 28, 200825 counties in North Carolina; 32 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Apr 28, 2008, 12:50 PM EDT for 25 counties in North Carolina; 32 counties in Virginia. It was in force for 55 min.

The area

The outline as issued.

The facts

Issued: Apr 28, 2008, 12:50 PM EDT (16:50 UTC)
Expired: Apr 28, 2008, 1:45 PM EDT
In force: 55 min
Issued by: the Storm Prediction Center

All 57 counties

Alamance County, NC, Bertie County, NC, Caswell County, NC, Chatham County, NC, Chowan County, NC, Durham County, NC, Edgecombe County, NC, Franklin County, NC, Gates County, NC, Granville County, NC, Halifax County, NC, Hertford County, NC, Johnston County, NC, Lee County, NC, Martin County, NC, Nash County, NC, Northampton County, NC, Orange County, NC, Perquimans County, NC, Person County, NC, Randolph County, NC, Vance County, NC, Wake County, NC, Warren 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 Suffolk, VA, City of Virginia Beach, VA, City of Williamsburg, VA, Dinwiddie County, VA, Gloucester County, VA, Greensville County, VA, Henrico County, VA, Isle of Wight County, VA, James City County, VA, Lunenburg County, VA, Mecklenburg County, VA, New Kent County, VA, Nottoway 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), 91 km from the middle of the area, began a volume at 16:53 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.

Tornado Watch 242Apr 28, 3:15 PM EDT

The nearest sounding before it

Roanoke, VA (KRNK), launched 12:00Z, 4.8 hours before the alert went out and 162 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: 60 J/kg
Mixed-layer CIN: -2 J/kg
Mixed-layer LCL: 491 m above ground
0-6 km bulk shear: 60 kt
0-1 km storm-relative helicity: 149 m²/s²
0-3 km storm-relative helicity: 151 m²/s²
Significant tornado parameter: -0.0
Supercell composite: -0.1

Open this sounding in Storm Lab

The text

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

000 
ACUS11 KWNS 281650
SWOMCD
SPC MCD 281650 
VAZ000-NCZ000-281745-

MESOSCALE DISCUSSION 0751
NWS STORM PREDICTION CENTER NORMAN OK
1150 AM CDT MON APR 28 2008

AREAS AFFECTED...NORTHEAST NC...SOUTHEAST VA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 281650Z - 281745Z

THUNDERSTORMS ARE LIKELY TO INCREASE/INTENSIFY THIS AFTERNOON ACROSS
PARTS OF NORTHEAST NC AND SOUTHEAST VA.  RELATIVELY WEAK INSTABILITY
IS LIKELY TO LIMIT OVERALL SEVERE THREAT...BUT TRENDS WILL BE
MONITORED EARLY THIS AFTERNOON FOR A POSSIBLE WATCH.

RECENT RADAR LOOPS INDICATE THAT A CLUSTER OF THUNDERSTORMS HAS
BEGUN TO INTENSIFY OVER ORANGE/PERSON/CASWELL COUNTIES OF NORTH
CENTRAL NC.  THESE STORMS APPEAR TO BE IN RIGHT ENTRANCE REGION OF
MID LEVEL JET MAX ROTATING NORTHWARD INTO PA/NY.  DESPITE NEAR
MOIST-ADIABATIC MID LEVEL LAPSE RATES...SURFACE DEWPOINTS IN THE 60S
AND TEMPERATURES SLOWLY WARMING TOWARD 70F ARE CONTRIBUTING TO
MUCAPE VALUES AROUND 1000 J/KG.  FORECAST SOUNDINGS IN THIS REGION
SHOW MODEST LOW LEVEL AND DEEP LAYER VERTICAL SHEAR PROFILES
SUFFICIENT FOR SUPERCELL STRUCTURES /EFFECTIVE HELICITY OF 100-200
M2/S2 AND EFFECTIVE SHEAR OF 35-40 KNOTS/.  LOCALLY GUSTY WINDS OR
BRIEF TORNADOES WILL BE POSSIBLE FROM STRONGER CELLS.  HAIL THREAT
APPEARS MINIMAL DUE TO WARM TEMPERATURES ALOFT AND WEAK CAPE.

..HART.. 04/28/2008

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

ATTN...WFO...AKQ...MHX...RAH...RNK...

35747993 36697908 37477758 37597669 37267600 36597587
35897672 35417841 35427975

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 28, 3:16 PM EDT	Tornado Watch	SPC	Beaufort, Bertie, Camden, Chowan, Currituck, Dare and 15 more	5 hr
Apr 28, 4:28 PM EDT	Mesoscale Discussion	SPC	Beaufort, Bertie, Camden, Chowan, Craven, Currituck and 18 more	92 min
Apr 28, 6:45 PM EDT	Mesoscale Discussion	SPC	Beaufort, Bertie, Camden, Chowan, Currituck, Dare and 10 more	60 min

Nearby

Mesoscale Discussions in Virginia, 2008 Mesoscale Discussions in North Carolina, 2008 Every mesoscale discussion in 2008

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.