Alert archive / Virginia / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 402
The Storm Prediction Center issued this severe thunderstorm watch at Jul 29, 2021, 3:00 PM EDT for 11 counties in Maryland; 42 counties in Virginia; 8 counties in West Virginia. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Jul 29, 2021, 3:00 PM EDT (19:00 UTC)
- Expired
- Jul 29, 2021, 9:00 PM EDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 61 counties
Allegany County, MD, Calvert County, MD, Charles County, MD, Dorchester County, MD, Garrett County, MD, Montgomery County, MD, Prince George's County, MD, Saint Mary's County, MD, Somerset County, MD, Wicomico County, MD, Worcester County, MD, Albemarle County, VA, Arlington County, VA, Augusta 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 Harrisonburg, VA, City of Manassas, VA, City of Manassas Park, VA, City of Staunton, VA, City of Waynesboro, VA, City of Winchester, VA, Clarke County, VA, Culpeper County, VA, Essex County, VA, Fairfax County, VA, Fauquier County, VA, Fluvanna County, VA, Frederick County, VA, Greene County, VA, Highland County, VA, King George County, VA, Lancaster County, VA, Loudoun County, VA, Louisa County, VA, Madison County, VA, Nelson County, VA, Northumberland County, VA, Orange County, VA, Page County, VA, Prince William County, VA, Rappahannock County, VA, Richmond County, VA, Rockingham County, VA, Shenandoah County, VA, Spotsylvania County, VA, Stafford County, VA, Warren County, VA, Westmoreland County, VA, Berkeley County, WV, Grant County, WV, Hampshire County, WV, Hardy County, WV, Jefferson County, WV, Mineral County, WV, Morgan County, WV, Pendleton County, WV
The radar
The Sterling radar (KLWX), 22 km from the middle of the area, began a volume at 19:00 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 40%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 20%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 60%
Warnings issued inside it
11 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 29, 4:40 PM EDT | Severe Thunderstorm Warning | LWX | Montgomery, Prince George's | 50 min |
| Jul 29, 4:45 PM EDT | Severe Thunderstorm Warning | LWX | Fauquier, Prince William, Stafford, City of Manassas, City of Manassas Park | 45 min |
| Jul 29, 4:59 PM EDT | Severe Thunderstorm Warning | LWX | Charles | 46 min |
| Jul 29, 5:01 PM EDT | Severe Thunderstorm Warning | LWX | Montgomery, Prince George's | 29 min |
| Jul 29, 5:21 PM EDT | Severe Thunderstorm Warning | LWX | King George, Spotsylvania, Stafford, City of Fredericksburg | 24 min |
| Jul 29, 5:23 PM EDT | Tornado Warning | LWX | Spotsylvania, Stafford, City of Fredericksburg | 25 min |
| Jul 29, 5:27 PM EDT | Severe Thunderstorm Warning | AKQ | Caroline | 33 min |
| Jul 29, 5:30 PM EDT | Severe Thunderstorm Warning | LWX | Anne Arundel, Calvert, Prince George's | 40 min |
| Jul 29, 5:55 PM EDT | Severe Thunderstorm Warning | AKQ | Caroline, Essex, King and Queen, Westmoreland | 35 min |
| Jul 29, 6:19 PM EDT | Severe Thunderstorm Warning | AKQ | Essex, King and Queen, King William, Richmond | 41 min |
| Jul 29, 6:48 PM EDT | Severe Thunderstorm Warning | AKQ | Essex, Gloucester, James City, King and Queen, King William, Middlesex and 1 more | 42 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Washington/Dulle, VA (KIAD), launched 12:00Z, 7.0 hours before the alert went out and 15 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
- 269 J/kg
- Mixed-layer CIN
- -91 J/kg
- Mixed-layer LCL
- 893 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km storm-relative helicity
- 62 m²/s²
- 0-3 km storm-relative helicity
- 62 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.2
The text
As transmitted.
332 WWUS20 KWNS 291856 SEL2 SPC WW 291856 DCZ000-MDZ000-VAZ000-WVZ000-CWZ000-300100- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 402 NWS Storm Prediction Center Norman OK 300 PM EDT Thu Jul 29 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of District Of Columbia Western Maryland and the Eastern Shore Northern Virginia Eastern Panhandle of West Virginia Coastal Waters * Effective this Thursday afternoon and evening from 300 PM until 900 PM EDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...Thunderstorms are expected to develop soon along the mountains of western Virginia and spread eastward across the watch area. The strongest cells will be capable of damaging wind gusts and hail. The severe thunderstorm watch area is approximately along and 45 statute miles north and south of a line from 60 miles west southwest of Martinsburg WV to 40 miles east northeast of Wallops VA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU2). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 401... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27030. ...Hart
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 29, 2:23 PM EDT | Tornado Watch | SPC | Kent, New Castle, Sussex | 8 hr |
| Jul 29, 4:26 PM EDT | Mesoscale Discussion | SPC | Kent, New Castle | 94 min |
| Jul 29, 11:58 AM EDT | Mesoscale Discussion | SPC | Allegany, Garrett | 2 hr |
| Jul 29, 1:21 PM EDT | Mesoscale Discussion | SPC | Carroll, Frederick, Washington | 114 min |
| Jul 29, 3:13 PM EDT | Severe Thunderstorm Watch | SPC | Barbour, Brooke, Calhoun, Doddridge, Gilmer, Hancock and 19 more | 7 hr |
| Jul 29, 6:34 PM EDT | Mesoscale Discussion | SPC | Brooke, Doddridge, Hancock, Harrison, Marion, Marshall and 8 more | 116 min |
Nearby
Severe Thunderstorm Watches in Virginia, 2021Severe Thunderstorm Watches in Maryland, 2021Severe Thunderstorm Watches in West Virginia, 2021Every severe thunderstorm watch 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.