Alert archive / Virginia / Mesoscale Discussions in 2023

Mesoscale Discussion 1521

July 13, 20234 states

The Storm Prediction Center issued this mesoscale discussion at Jul 13, 2023, 2:36 PM EDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Jul 13, 2023, 2:36 PM EDT (18:36 UTC)
Expired: Jul 13, 2023, 5:00 PM EDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

All 109 counties

Allegany County, MD, Anne Arundel County, MD, Baltimore County, MD, Carroll County, MD, Charles County, MD, City of Baltimore, MD, Frederick County, MD, Harford County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Washington County, MD, Adams County, PA, Bedford County, PA, Berks County, PA, Carbon County, PA, Columbia County, PA, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Fulton County, PA, Huntingdon County, PA, Juniata County, PA, Lackawanna County, PA, Lancaster County, PA, Lebanon County, PA, Lehigh County, PA, Luzerne County, PA, Lycoming County, PA, Mifflin County, PA, Monroe County, PA, Montour County, PA, Northampton County, PA, Northumberland County, PA, Perry County, PA, Schuylkill County, PA, Snyder County, PA, Sullivan County, PA, Union County, PA, Wyoming County, PA, York County, PA, Albemarle County, VA, Alleghany County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Augusta County, VA, Bath County, VA, Bedford County, VA, Botetourt County, VA, Buckingham County, VA, Campbell County, VA, Caroline County, VA, City of Alexandria, VA, City of Buena Vista, VA, City of Charlottesville, VA, City of Covington, VA, City of Fairfax, VA, City of Falls Church, VA, City of Fredericksburg, VA, City of Harrisonburg, VA, City of Lexington, VA, City of Lynchburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Roanoke, VA, City of Salem, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Craig County, VA, Culpeper County, VA, Cumberland County, VA, Fairfax County, VA, Fauquier County, VA, Floyd County, VA, Fluvanna County, VA, Franklin County, VA, Frederick County, VA, Goochland County, VA, Greene County, VA, Highland County, VA, King George County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Montgomery County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Pittsylvania County, VA, Prince Edward County, VA, Prince William County, VA, Rappahannock County, VA, Roanoke County, VA, Rockbridge County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Berkeley County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV, Pendleton County, WV

The radar

The Sterling radar (KLWX), 54 km from the middle of the area, began a volume at 18:36 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, 6.6 hours before the alert went out and 61 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: 96 J/kg
Mixed-layer CIN: -216 J/kg
Mixed-layer LCL: 1477 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 87 m²/s²
0-3 km storm-relative helicity: 83 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

041 
ACUS11 KWNS 131837
SWOMCD
SPC MCD 131836 
PAZ000-MDZ000-DCZ000-VAZ000-WVZ000-132100-

Mesoscale Discussion 1521
NWS Storm Prediction Center Norman OK
0136 PM CDT Thu Jul 13 2023

Areas affected...Portions of eastern WV...VA...DC...western/central
MD...and central/eastern PA

Concerning...Severe potential...Watch possible 

Valid 131836Z - 132100Z

Probability of Watch Issuance...40 percent

SUMMARY...Some threat for damaging winds and hail may exist as
thunderstorms move eastward this afternoon. The need for a watch
remains unclear, but trends will be monitored.

DISCUSSION...Scattered thunderstorms have developed this afternoon
across parts of the central Appalachians. More isolated activity is
attempting to deepen across parts of north-central into northeastern
PA, closer to the upper trough over NY and southern Quebec. A
surface lee trough is present along/east of the Appalachians/Blue
Ridge Mountains, with ample daytime heating acting to steepen
low-level lapse rates. Latest mesoanalysis shows a relative minimum
in instability along/east of the lee trough across parts of
central/eastern VA into central MD and eastern PA. This area appears
to have shallower low-level moisture based on area 12Z soundings,
and some lingering MLCIN.

Still, various RAP/NAM forecast soundings across this region suggest
that a well mixed boundary layer will support at least an isolated
damaging wind threat with any convection that can spread eastward
off the higher terrain this afternoon and evening. Around 25-35 kt
of deep-layer shear should also foster some thunderstorm
organization, with multicells to marginal supercells possible. Some
hail may occur with the strongest cores. With better large-scale
ascent focused farther north across NY and New England, overall
thunderstorm coverage remains uncertain. The need for a Severe
Thunderstorm Watch this afternoon is also unclear, but observational
trends will be closely monitored.

..Gleason/Bunting.. 07/13/2023

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

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

LAT...LON   36898068 39057921 39887863 41777665 41747536 40947513
            38517672 37207843 36657958 36898068

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 13, 11:58 AM EDT	Mesoscale Discussion	SPC	Susquehanna	2 hr
Jul 13, 1:56 PM EDT	Severe Thunderstorm Watch	SPC	Fayette, Greene	7 hr
Jul 13, 1:26 PM EDT	Mesoscale Discussion	SPC	Barbour, Boone, Braxton, Cabell, Calhoun, Clay and 31 more	64 min
Jul 13, 4:42 PM EDT	Mesoscale Discussion	SPC	Barbour, Braxton, Cabell, Calhoun, Clay, Doddridge and 25 more	93 min
Jul 13, 7:07 PM EDT	Mesoscale Discussion	SPC	Boone, Fayette, Greenbrier, Lincoln, Logan, Mingo and 5 more	53 min

Nearby

Mesoscale Discussions in Virginia, 2023 Mesoscale Discussions in Pennsylvania, 2023 Mesoscale Discussions in Maryland, 2023 Every mesoscale discussion in 2023

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.