Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 370
The Storm Prediction Center issued this mesoscale discussion at Apr 11, 2021, 4:54 PM EDT for 4 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 11, 2021, 4:54 PM EDT (20:54 UTC)
- Expired
- Apr 11, 2021, 7:00 PM EDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
All 41 counties
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, Cumberland County, PA, Dauphin County, PA, Franklin County, PA, Juniata County, PA, Lancaster County, PA, Lebanon County, PA, Perry County, PA, York County, PA, Arlington 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, Madison County, VA, Orange County, VA, Prince William County, VA, Rappahannock County, VA, Spotsylvania County, VA, Stafford County, VA, Berkeley County, WV, Jefferson County, WV
The radar
The Sterling radar (KLWX), 67 km from the middle of the area, began a volume at 20:56 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, 8.9 hours before the alert went out and 69 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
- 26 J/kg
- Mixed-layer CIN
- 0 J/kg
- Mixed-layer LCL
- 506 m above ground
- 0-6 km bulk shear
- 31 kt
- 0-1 km storm-relative helicity
- -68 m²/s²
- 0-3 km storm-relative helicity
- 36 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
126
ACUS11 KWNS 112054
SWOMCD
SPC MCD 112054
PAZ000-MDZ000-VAZ000-DCZ000-WVZ000-112300-
Mesoscale Discussion 0370
NWS Storm Prediction Center Norman OK
0354 PM CDT Sun Apr 11 2021
Areas affected...Northern Virginia...Maryland...southern
Pennsylvania
Concerning...Severe potential...Watch unlikely
Valid 112054Z - 112300Z
Probability of Watch Issuance...5 percent
SUMMARY...A few strong to locally severe thunderstorms may develop
through late afternoon/early evening, primarily across parts of
northern Virginia and central Maryland into southern Pennsylvania.
DISCUSSION...Convection has struggled to deepen this afternoon
near/just ahead of an eastward-moving cold front, owing to factors
such as limited boundary layer moisture and weak convergence owing
to veered near-surface winds within the pre-frontal warm sector.
While surface dewpoints continue to drop coincident with ample
boundary layer mixing, a recent modest increase in convergence has
been noted in vicinity of the front and near/just east of the Blue
Ridge along with increasing cumuliform development.
Additional development and convective intensification is still
plausible through the late afternoon/early evening, particularly
within a corridor across northern Virginia/DC vicinity/central
Maryland into south-central Pennsylvania where low-level convergence
should maximize in vicinity of surface low/triple point. Where
thunderstorms are able to develop and sustain, a warm and well-mixed
boundary layer would support the possibility of some strong/locally
damaging wind gusts, aside from the possibility of some hail.
..Guyer/Thompson.. 04/11/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...CTP...LWX...
LAT...LON 40707728 40537652 40027590 39337606 38087714 38137818
38467834 39257810 40407794 40707728Nearby
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.