Alert archive / Virginia / Mesoscale Discussions in 2021

Mesoscale Discussion 1524

August 14, 20217 counties in Maryland; 33 counties in North Carolina; 79 counties in Virginia

The Storm Prediction Center issued this mesoscale discussion at Aug 14, 2021, 1:10 PM EDT for 7 counties in Maryland; 33 counties in North Carolina; 79 counties in Virginia. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Aug 14, 2021, 1:10 PM EDT (17:10 UTC)
Expired: Aug 14, 2021, 3:15 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

All 119 counties

Calvert County, MD, Charles County, MD, Dorchester County, MD, Prince George's County, MD, Saint Mary's County, MD, Somerset County, MD, Talbot County, MD, Alamance County, NC, Alexander County, NC, Cabarrus County, NC, Caswell County, NC, Chatham County, NC, Davidson County, NC, Davie County, NC, Durham County, NC, Forsyth County, NC, Franklin County, NC, Granville County, NC, Guilford County, NC, Halifax County, NC, Harnett County, NC, Iredell County, NC, Lee County, NC, Montgomery County, NC, Moore County, NC, Nash County, NC, Northampton County, NC, Orange County, NC, Person County, NC, Randolph County, NC, Rockingham County, NC, Rowan County, NC, Stanly County, NC, Stokes County, NC, Surry County, NC, Vance County, NC, Wake County, NC, Warren County, NC, Wilkes County, NC, Yadkin 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, Carroll County, VA, Charles City County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Colonial Heights, VA, City of Danville, VA, City of Emporia, 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 Newport News, VA, City of Petersburg, VA, City of Richmond, VA, City of Roanoke, VA, City of Williamsburg, VA, Culpeper County, VA, Cumberland County, VA, Dinwiddie County, VA, Essex County, VA, Fairfax County, VA, Floyd County, VA, Fluvanna County, VA, Franklin County, VA, Gloucester County, VA, Goochland County, VA, Greene County, VA, Greensville County, VA, Halifax County, VA, Hanover County, VA, Henrico County, VA, Henry 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, Madison County, VA, Mathews County, VA, Mecklenburg County, VA, Middlesex County, VA, Nelson County, VA, New Kent County, VA, Northumberland County, VA, Nottoway County, VA, Orange County, VA, Patrick County, VA, Pittsylvania County, VA, Powhatan County, VA, Prince Edward County, VA, Prince George County, VA, Prince William County, VA, Richmond County, VA, Southampton County, VA, Spotsylvania County, VA, Stafford County, VA, Surry County, VA, Sussex County, VA, Westmoreland County, VA, York County, VA

The radar

The Norfolk radar (KAKQ), 116 km from the middle of the area, began a volume at 17:11 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, 5.2 hours before the alert went out and 108 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: 154 J/kg
Mixed-layer CIN: -126 J/kg
Mixed-layer LCL: 1147 m above ground
0-6 km bulk shear: 20 kt
0-1 km storm-relative helicity: 32 m²/s²
0-3 km storm-relative helicity: 52 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

968 
ACUS11 KWNS 141710
SWOMCD
SPC MCD 141710 
VAZ000-MDZ000-DCZ000-NCZ000-141915-

Mesoscale Discussion 1524
NWS Storm Prediction Center Norman OK
1210 PM CDT Sat Aug 14 2021

Areas affected...North Carolina...Virginia...and east Maryland

Concerning...Severe potential...Watch possible 

Valid 141710Z - 141915Z

Probability of Watch Issuance...40 percent

SUMMARY...Thunderstorms are expected to gradually develop through
the mid/late afternoon hours and may pose a damaging wind risk.
Trends will be monitored, and a watch may be needed.

DISCUSSION...Latest GOES imagery shows generally clear skies over
VA/NC with a few cumulus fields developing along the Blue Ridge
Mountains from the Carolinas into western VA as well as across
central NC along a weakly confluent trough axis. The development of
these cumulus fields are indicative of boundary-layer
destabilization thanks to a combination of rich boundary-layer
moisture, minimal capping (as observed in regional 12z soundings),
and near-surface parcels approaching their convective temperatures
(generally in the upper 80s and low 90s) via strong insolation. RAP
analyses support this idea, showing diminishing MLCIN amid
increasing MLCAPE (up to 1500-2500 J/kg). Convective initiation is
already underway south of this region into SC/GA along the trough
axis where capping is weaker and confluence stronger. Similar storm
development is expected from NC northward into VA through the mid
afternoon hours along the trough axis and approaching weak cold
front as inhibition continues to erode. Deep-layer shear is fairly
weak, which will limit the overall potential for organized severe
storms. However, steepening low-level lapse rates may allow for
sporadic, but damaging, downburst winds with any cell or storm
clusters. Trends will be monitored, and a watch may be needed for
portions of central/eastern VA.

..Moore/Hart.. 08/14/2021

...Please see www.spc.noaa.gov for graphic product...

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

LAT...LON   36258136 37128030 38157874 38937737 39007635 38687580
            38287573 37627596 37067649 36597714 36047766 35577834
            35217925 35268008 35488109 36258136

Nearby

Mesoscale Discussions in Virginia, 2021 Mesoscale Discussions in North Carolina, 2021 Mesoscale Discussions in Maryland, 2021 Every mesoscale discussion in 2021

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.