Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1284
The Storm Prediction Center issued this mesoscale discussion at Jul 14, 2021, 3:24 PM EDT for 6 counties in Maryland; 24 counties in Virginia. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Jul 14, 2021, 3:24 PM EDT (19:24 UTC)
- Expired
- Jul 14, 2021, 5:30 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 30 counties
Anne Arundel County, MD, Calvert County, MD, Charles County, MD, Howard County, MD, Montgomery County, MD, Prince George's County, MD, Arlington County, VA, Caroline 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, Clarke County, VA, Culpeper County, VA, Fairfax County, VA, Fauquier County, VA, Greene County, VA, King George County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Orange County, VA, Prince William County, VA, Rappahannock County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA
The radar
The Sterling radar (KLWX), 49 km from the middle of the area, began a volume at 19:27 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, 7.4 hours before the alert went out and 46 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.
- Mixed-layer CAPE
- 58 J/kg
- Mixed-layer CIN
- -111 J/kg
- Mixed-layer LCL
- 1557 m above ground
- 0-6 km bulk shear
- 33 kt
- 0-1 km storm-relative helicity
- -3 m²/s²
- 0-3 km storm-relative helicity
- 62 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
418
ACUS11 KWNS 141925
SWOMCD
SPC MCD 141924
MDZ000-VAZ000-DCZ000-WVZ000-142130-
Mesoscale Discussion 1284
NWS Storm Prediction Center Norman OK
0224 PM CDT Wed Jul 14 2021
Areas affected...northern Virginia into Maryland
Concerning...Severe potential...Watch unlikely
Valid 141924Z - 142130Z
Probability of Watch Issuance...20 percent
SUMMARY...A cluster of storms may produce strong wind gusts capable
of localized damage over the next few hours.
DISCUSSION...Steep low-level lapse rates have developed near a weak
surface trough, resulting in deep mixed layers per modified forecast
soundings. A small cluster of storms has already formed over
northern VA, consistent with earlier CAM depictions, and these cells
are likely to propagate east/southeast over the next few hours.
Deep-layer shear is weak, but perhaps sufficient to sustain and
advect these storms eastward given the deep mixed layers and
sufficient instability. As such, localized damaging gusts cannot be
ruled out. Storms are expected to remain tied to the diurnal cycle,
and weaken by evening.
..Jewell/Bunting.. 07/14/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...LWX...
LAT...LON 37937729 37877831 38107861 38397842 39037828 39317779
39367706 39187662 38757648 38357649 38227660 37937729Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in Maryland, 2021Every 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.