Alert archive / Virginia / Mesoscale Discussions in 2021

Mesoscale Discussion 1462

August 10, 20216 states

The Storm Prediction Center issued this mesoscale discussion at Aug 10, 2021, 2:30 PM EDT for 6 states. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Aug 10, 2021, 2:30 PM EDT (18:30 UTC)
Expired: Aug 10, 2021, 5:00 PM EDT
In force: 3 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 5%

All 78 counties

New Castle County, DE, Anne Arundel County, MD, Baltimore County, MD, Calvert County, MD, Caroline County, MD, Carroll County, MD, Cecil County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Kent County, MD, Montgomery County, MD, Prince George's County, MD, Queen Anne's County, MD, Saint Mary's County, MD, Talbot County, MD, Camden County, NJ, Gloucester County, NJ, Hunterdon County, NJ, Salem County, NJ, Adams County, PA, Berks County, PA, Bucks County, PA, Chester County, PA, Cumberland County, PA, Dauphin County, PA, Delaware County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Montgomery County, PA, Philadelphia County, PA, Schuylkill County, PA, York County, PA, Albemarle County, VA, Amelia County, VA, Appomattox County, VA, Arlington County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, Charlotte County, VA, Chesterfield County, VA, City of Alexandria, VA, City of Charlottesville, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Richmond, VA, Clarke County, VA, Culpeper County, VA, Cumberland County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Goochland County, VA, Hanover County, VA, King George County, VA, King William County, VA, Loudoun County, VA, Louisa County, VA, Lunenburg County, VA, Madison County, VA, Nottoway County, VA, Orange County, VA, Powhatan County, VA, Prince Edward County, VA, Prince William County, VA, Rappahannock County, VA, Spotsylvania County, VA, Stafford County, VA, Westmoreland County, VA, Jefferson County, WV

The radar

The Sterling radar (KLWX), 50 km from the middle of the area, began a volume at 18:29 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

Washington/Dulle, VA (KIAD), launched 12:00Z, 6.5 hours before the alert went out and 47 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: 529 J/kg
Mixed-layer CIN: -120 J/kg
Mixed-layer LCL: 1096 m above ground
0-6 km bulk shear: 14 kt
0-1 km storm-relative helicity: 37 m²/s²
0-3 km storm-relative helicity: 65 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

637 
ACUS11 KWNS 101831
SWOMCD
SPC MCD 101830 
NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-102100-

Mesoscale Discussion 1462
NWS Storm Prediction Center Norman OK
0130 PM CDT Tue Aug 10 2021

Areas affected...Portions of central/eastern VA...DC...MD...DE...
southeastern PA...and western NJ

Concerning...Severe potential...Watch unlikely 

Valid 101830Z - 102100Z

Probability of Watch Issuance...5 percent

SUMMARY...Mainly isolated tree damage may occur with storms this
afternoon. Watch issuance is not expected.

DISCUSSION...Convection is beginning to increase in coverage over
parts of the Blue Ridge Mountains in central VA. Another isolated
storm was located in south-central PA as of 1830Z. Current
expectations are for scattered storms to develop through the
remainder of the afternoon along/east of the Blue Ridge along a weak
surface trough. Mid-level flow is quite weak across VA/MD (20 kt or
less per recent VWP estimated from KLWX), and it strengthens only
modestly with northward extent into south-central PA. Still, with
around 1500-2000 J/kg of MLCAPE present and somewhat steepened
low-level lapse rates, a mix of pulse storms and perhaps a small
cluster or two may ultimately occur. Wet microbursts and/or gusty
outflow winds capable or producing mainly isolated tree damage will
likely be the main severe threat. Given the lack of stronger
low/mid-level flow, the overall severe threat is expected to remain
too marginal to justify watch issuance.

..Gleason/Thompson.. 08/10/2021

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

ATTN...WFO...PHI...AKQ...CTP...LWX...RNK...

LAT...LON   37717892 38227838 39177808 40617691 40827612 40677490
            40077464 38627604 37787696 37167774 36737829 36867889
            37227929 37717892

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 10, 12:12 PM EDT	Mesoscale Discussion	SPC	Allegheny, Armstrong, Beaver, Butler, Fayette, Greene and 2 more	3 hr

Nearby

Mesoscale Discussions in Virginia, 2021 Mesoscale Discussions in Maryland, 2021 Mesoscale Discussions in Pennsylvania, 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.