Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1616
The Storm Prediction Center issued this mesoscale discussion at Aug 27, 2021, 1:41 PM EDT for 4 states. It was in force for 3 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 27, 2021, 1:41 PM EDT (17:41 UTC)
- Expired
- Aug 27, 2021, 4:15 PM EDT
- In force
- 3 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
All 43 counties
Anne Arundel County, MD, Baltimore County, MD, Calvert 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, Washington County, MD, Adams County, PA, Cumberland County, PA, Franklin County, PA, Lancaster County, PA, York County, PA, Arlington County, VA, Caroline County, VA, City of Alexandria, 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, 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, Jefferson County, WV
The radar
The Sterling radar (KLWX), 45 km from the middle of the area, began a volume at 17:42 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, 5.7 hours before the alert went out and 40 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
- 780 J/kg
- Mixed-layer CIN
- -92 J/kg
- Mixed-layer LCL
- 983 m above ground
- 0-6 km bulk shear
- 8 kt
- 0-1 km storm-relative helicity
- 13 m²/s²
- 0-3 km storm-relative helicity
- 41 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
268
ACUS11 KWNS 271741
SWOMCD
SPC MCD 271741
PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-272015-
Mesoscale Discussion 1616
NWS Storm Prediction Center Norman OK
1241 PM CDT Fri Aug 27 2021
Areas affected...Parts of the Mid Atlantic
Concerning...Severe potential...Watch unlikely
Valid 271741Z - 272015Z
Probability of Watch Issuance...20 percent
SUMMARY...Storm coverage is expected to increase this afternoon,
with isolated-to-scattered damaging wind gusts possible.
DISCUSSION...Early this afternoon, a weak midlevel shortwave trough
is moving slowly eastward toward the Mid Atlantic, with convection
beginning to develop across the higher terrain. Downstream, strong
heating of a very moist boundary layer is resulting in MLCAPE of
1500-2000 J/kg as of 17Z, with some further increase in buoyancy
expected through the afternoon. Storm coverage is expected to
gradually increase this afternoon in advance of the shortwave
trough. Deep-layer shear is generally weak across the region and
storms may tend to remain disorganized, with a primary risk of
isolated downburst wind gusts within the high PW environment.
However, slightly stronger westerly midlevel flow along the southern
flank of the shortwave trough may promote some loosely organized
clusters across MD/DC/northern VA, which could pose a slightly more
organized damaging wind risk.
Given the weak deep-layer shear across the region, watch issuance is
currently considered unlikely, but this will be reevaluated if more
organized outflow-driven clusters develop or appear imminent.
..Dean/Dial.. 08/27/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...CTP...LWX...
LAT...LON 38837830 40037771 40287700 40327665 40127586 39927571
39657562 39107589 38797625 38447659 38147707 37957738
37897802 38367851 38837830Nearby
Mesoscale Discussions in Virginia, 2021Mesoscale Discussions in Maryland, 2021Mesoscale Discussions in Pennsylvania, 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.