Alert archive / Virginia / Mesoscale Discussions in 2021
Mesoscale Discussion 1510
The Storm Prediction Center issued this mesoscale discussion at Aug 13, 2021, 12:33 PM EDT for 4 states. It was in force for 87 min.
The area
The outline as issued.
The facts
- Issued
- Aug 13, 2021, 12:33 PM EDT (16:33 UTC)
- Expired
- Aug 13, 2021, 2:00 PM EDT
- In force
- 87 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
All 76 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, Fulton County, PA, Lancaster County, PA, Lebanon County, PA, Perry County, PA, York County, PA, Albemarle County, VA, Amherst County, VA, Appomattox County, VA, Arlington County, VA, Augusta 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 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, Culpeper County, VA, Cumberland County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Franklin County, VA, Frederick County, VA, Goochland County, VA, Greene County, VA, King George County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Nelson County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock 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, Morgan County, WV
The radar
The Sterling radar (KLWX), 63 km from the middle of the area, began a volume at 16:37 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 4.6 hours before the alert went out and 68 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
- 313 J/kg
- Mixed-layer CIN
- -199 J/kg
- Mixed-layer LCL
- 1675 m above ground
- 0-6 km bulk shear
- 8 kt
- 0-1 km storm-relative helicity
- -11 m²/s²
- 0-3 km storm-relative helicity
- 58 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
232
ACUS11 KWNS 131633
SWOMCD
SPC MCD 131633
PAZ000-MDZ000-VAZ000-DCZ000-WVZ000-131800-
Mesoscale Discussion 1510
NWS Storm Prediction Center Norman OK
1133 AM CDT Fri Aug 13 2021
Areas affected...southern PA...MD...central and northern VA
Concerning...Severe potential...Watch possible
Valid 131633Z - 131800Z
Probability of Watch Issuance...40 percent
SUMMARY...Isolated gusts 45-60 mph are forecast with the stronger
storms this afternoon. Localized pockets of wind damage are
expected.
DISCUSSION...Visible-satellite imagery shows a swelling cumulus
field and the early stages of thunderstorm development near the
WV/VA border. Surface temperatures have warmed into the lower 90s
with dewpoints ranging from near 70 degrees west and mid-upper 70s
near Chesapeake Bay. Area 88D VAD data shows weak tropospheric flow
indicative of pulse thunderstorms. Steep low-level lapse rates with
2 inches precipitable water will favor water-loaded downdrafts. The
more intense downdrafts will be capable of gusts 45-60 mph with a
localized risk for wind damage near the heavier bursts. A severe
thunderstorm watch will be considered over the next hour or so.
..Smith/Hart.. 08/13/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...PHI...AKQ...CTP...LWX...RNK...
LAT...LON 36968039 40307823 40527675 40307609 39667610 37957714
36747971 36968039SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 13, 1:11 PM EDT | Severe Thunderstorm Watch | SPC | Anne Arundel, Baltimore, Calvert, Caroline, Carroll, Cecil and 13 more | 7 hr |
| Aug 13, 4:48 PM EDT | Mesoscale Discussion | SPC | Anne Arundel, Baltimore, Cecil, Charles, Harford, Howard and 2 more | 87 min |
| Aug 13, 6:02 PM EDT | Mesoscale Discussion | SPC | Wicomico, Worcester | 58 min |
| Aug 12, 10:08 PM EDT | Mesoscale Discussion | SPC | Berks, Bucks, Carbon, Chester, Columbia, Cumberland and 22 more | 67 min |
| Aug 13, 2:48 PM EDT | Mesoscale Discussion | SPC | Bradford, Cameron, Clinton, Lycoming, Potter, Sullivan and 2 more | 87 min |
| Aug 13, 3:29 PM EDT | Severe Thunderstorm Watch | SPC | Bradford, Clinton, Columbia, Lackawanna, Luzerne, Lycoming and 11 more | 7 hr |
| Aug 13, 4:46 PM EDT | Severe Thunderstorm Watch | SPC | Allegheny, Armstrong, Beaver, Butler, Clarion, Fayette and 9 more | 5 hr |
| Aug 13, 7:14 PM EDT | Mesoscale Discussion | SPC | Bradford, Columbia, Lackawanna, Luzerne, Lycoming, Monroe and 9 more | 61 min |
| Aug 13, 7:49 PM EDT | Mesoscale Discussion | SPC | Allegheny, Armstrong, Beaver, Butler, Cambria, Clarion and 13 more | 56 min |
| Aug 13, 1:13 PM EDT | Mesoscale Discussion | SPC | Cabell, Calhoun, Clay, Doddridge, Gilmer, Harrison and 15 more | 2 hr |
Nearby
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.