Mesoscale Discussion 1787

Issued

Sep 28, 2021, 4:16 PM EDT (20:16 UTC)

Expired

Sep 28, 2021, 6:15 PM EDT

In force

119 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Albemarle County, VA, Buckingham County, VA, City of Charlottesville, VA, City of Fredericksburg, VA, City of Waynesboro, VA, Culpeper County, VA, Fauquier County, VA, Fluvanna County, VA, Greene County, VA, Louisa County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Rappahannock County, VA, Spotsylvania County, VA, Stafford County, VA

The Sterling radar (KLWX), 91 km from the middle of the area, began a volume at 20:17 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.

352 
ACUS11 KWNS 282017
SWOMCD
SPC MCD 282016 
VAZ000-282215-

Mesoscale Discussion 1787
NWS Storm Prediction Center Norman OK
0316 PM CDT Tue Sep 28 2021

Areas affected...Parts of northwestern/northern Virginia

Concerning...Severe potential...Watch unlikely 

Valid 282016Z - 282215Z

Probability of Watch Issuance...5 percent

SUMMARY...Widely scattered strong storms may develop through 5-7 PM
EDT, and pose at least some risk for severe hail and locally strong
wind gusts, particularly near and east/south of the Charlottesville
area.

DISCUSSION...To the north of a weakening mid-level speed maximum
(around 40 kt near the 500 mb level) propagating across the Roanoke
vicinity, the latest Rapid Refresh suggests that boundary-layer
destabilization may become maximized during the next few hours along
and to the lee of the Blue Ridge.  Beneath an elongated mid-level
cold pocket aligned along this corridor, lower/mid tropospheric
lapse rates are becoming rather steep, with sufficient low-level
moisture to contribute to mixed-layer CAPE in excess of 1000 J/kg,
and perhaps locally as large as 2000 J/kg.

Mid/upper forcing for ascent to support thunderstorm initiation is
unclear, but widely scattered areas of deepening convective
development are becoming evident along the higher terrain.  This
includes one area to the northwest of Charlottesville (near
Staunton), where 2-3 mb 2-hourly surface pressure falls were
apparent in 19Z observational data.  In the presence of deep-layer
shear at least marginally supportive of organized thunderstorm
development, the environment appears conducive to widely scattered
storms, perhaps including an isolated supercell structure or two,
capable of producing severe hail.  Locally strong surface gusts also
appear possible, before activity weakens this evening with the loss
of daytime heating.

..Kerr/Thompson.. 09/28/2021

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

ATTN...WFO...AKQ...LWX...RNK...

LAT...LON   38837776 38617741 38287738 38077755 37917782 37547860
            37817922 38367894 38757823 38837776

Mesoscale Discussions in Virginia, 2021Every mesoscale discussion in 2021

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.