Showers and thunderstorms developed near a boundary over central Virginia. Anomalous moisture was present, and the storm motion was slow which led to areas of flooding and flash flooding.
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The episode as NWS LWX wrote it up.
Showers and thunderstorms developed near a boundary over central Virginia. Anomalous moisture was present, and the storm motion was slow which led to areas of flooding and flash flooding.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Baltimore/Washington wrote its last area forecast discussion before the first event at Aug 21, 8:51 AM EST, 54 minutes earlier.
Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 951 AM EDT Sun Aug 21 2022 .SYNOPSIS... A cold front will approach from the Ohio River Valley today, then slowly cross the region through Tuesday. The front will likely stall just offshore through mid week as high pressure builds in its wake. Another frontal system likely approaches late in the week. && .NEAR TERM /THROUGH TONIGHT/... The regional radar mosaic depicts an active morning across the region. A band of moderate to heavy showers and thunderstorms were moving northeastward into the Potomac Highlands and the central Shenandoah Valley. Based on upstream observations, 1 to 1.50 inches of rain have fallen in an hour with this cluster. All of this activity will work its way across the Blue Ridge and toward the DC metro area within the next few hours. In terms of the current environment, the 12Z IAD sounding yielded a very moist sounding with a precipitable water of 1.83 inches. Based on mid/late August climatology, this value is around the 90th percentile. With near saturation to 250-mb, updrafts should not deal with notable dry air entrainment processes. Thus, storms should be highly efficient in heavy rainfall production. Ample cloud cover is expected across the forecast area today, but it should be thin enough for at least some limited daytime heating to ensue. Temperatures are expected to make it in the upper 70s across western portions of the forecast area, with low-mid 80s further east. A slow moving mid-upper level trough is evident on water vapor imagery over the western Great Lakes this morning. Over the course of the day, this feature will slowly drift eastward, placing us in southwesterly flow aloft. The low-level mass response ahead of this feature will cause southerly flow to advect an increasingly moist airmass into the region, with precipitable water values climbing to near 2 inches by later today. Large scale ascent downstream of the approaching trough coupled with daytime heating will lead to the development of numerous showers and thunderstorms this afternoon. These storms will initially form to the west of the Blue Ridge during the early-mid afternoon hours, before spreading further east during the evening. The main concern today will be heavy rainfall and resultant hydro related issues. Today's environment checks several boxes for heavy rain producing storms. Model soundings show nearly saturated profiles through a deep layer, along with the aforementioned well above normal precipitable water values. This will provide ample moisture to any storms, allowing for efficient rainfall production, while also limiting any cold pool driven propagation (thereby making training storm motions a bit easier to achieve). Model soundings also show ample instability (CAPE values on the order of 1000-2000 J/kg), and strong low-level inflow values (greater than 20 knots in the 0-1 km layer). This will allow storms to have strong updrafts that process a lot of air, maximizing the amount of precipitation produced. Limiting factors for flash flooding include somewhat elevated flash flood guidance values (due to relatively dry antecedent conditions), as well as strong winds aloft, which may act to keep storms moving along at a decent clip. 00z CAMs are very consistent in producing localized hefty rainfall totals (all have localized maxima of 4+"), but are very inconsistent with respect to placement of the heaviest rain, which makes sense in the absence of a focusing low-level boundary. Confidence wasn't yet high enough to issue a Flood Watch, but we'll continue to monitor the threat for heavy rainfall and resultant flooding through the remainder of the day. Severe thunderstorms aren't expected to be much of a threat today, as the relatively moist profiles will limit evaporatively driven downburst potential. The threat for heavy rainfall may continue through the first half of the overnight to the east of the Blue Ridge with instability still in place, and the approaching large scale trough providing continued synoptic scale ascent. Storms should eventually wind down and move out of the area during the second half of the overnight. Lows overnight are expected to be in the mid 60s to low 70s. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The aforementioned mid-upper level trough will continue to ever so slowly drift eastward on Monday, with the trough axis still remaining upstream of the area. As a result, showers and thunderstorms are expected to form in response to daytime heating once again. While coverage of storms might not be quite as high as today, most locations will still stand a good chance of experiencing a storm during the afternoon or evening hours. Precipitable water values will be a tad bit lower than today, but will still remain elevated. Instability values will be on par with, or a little higher than today (generally around 1500-2000 J/kg). As a result, storms could still be heavy rainfall producers, although likely not as prolific as today. However, any rains will be falling on top of what could already be saturated ground. As a result, there will be at least some threat for hydro related issues. Although there will be a bit more CAPE, as well as slightly greater DCAPE values (as a little bit of dry air works in aloft), severe thunderstorms aren't expected to be a major threat. However, an isolated strong downburst or two can't be ruled out. Highs tomorrow are expected to be in the low 80s for most. The upper trough will slowly progress further eastward on Tuesday, with height rises expected locally. However, another shortwave will dig toward Lake Michigan, helping to reinforce the broader trough situated over the eastern half of the CONUS. With height rises aloft, and some drying out at low levels in westerly flow, coverage of any afternoon showers or thunderstorms is expected to remain low. Highs on Tuesday will climb into the low-mid 80s for most. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Mid/upper-level troughing, loosely tied to a persistent upper low near NE Canada, will weaken during the second half of the week before re-orienting itself over the middle of the country. At the surface, a weakening cold front will likely be stalled just off the coast Wednesday through Friday as weak high pressure builds in from the OH Valley and ridging (Bermuda high) builds offshore. Low probabilities for showers and thunderstorms may exist each afternoon and evening with the front lingering nearby. Another frontal system may approach by week's end. Added forcing with the front could offer higher chances of showers and thunderstorms. Temperatures are expected to be near normal for much of the second half of the upcoming week; this translates to highs in the mid/upper 80s and lows in the 60s to around 70 east of the mountains. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... Periods of MVFR to occasionally IFR ceilings are likely across CHO and MRB, while potentially impacting IAD as well. Some restrictions are possible this morning at CHO as a cluster of showers moves in from the southwest. It remains to be seen if this impacts downstream terminals. Improvement back to VFR is possible this afternoon. Widespread showers and thunderstorms are expected later this afternoon into this evening. The storms should form closer to MRB and CHO this afternoon and then spread eastward toward the major hubs this evening. Tried as best as possible to time the VCTS into a 4 hours window at each TAF site, but both showers and thunderstorms are possible over a fairly long time period. MVFR to IFR ceilings are also expected during the latter half of the overnight, with some fog possible as well. Conditions will improve back to VFR tomorrow morning, with showers and thunderstorms possible again tomorrow afternoon. Prevailing VFR conditions (outside of any storms) should continue into Tuesday, with lesser chances for a passing shower or storm Tuesday afternoon. Winds will be light out of the south for both today and tomorrow, before becoming light out of the west on Tuesday. Mainly VFR Wed-Thu with light S/SE flow. Patchy early AM fog is possible, as is a pop up PM shower/thunderstorm. && .MARINE... Predominantly sub-SCA magnitude southerly winds are expected over the waters through Monday. Winds may briefly reach low-end SCA levels in channeled southerly flow Monday afternoon. Sub- SCA westerly flow is expected on Tuesday. Southerly to southeasterly flow is expected as a front stalls and weakens offshore Wednesday into Thursday. A pop up shower or thunderstorm can't be ruled out each afternoon and evening, but at the moment it appears most of the time should be dry. && .TIDES/COASTAL FLOODING... Light onshore flow is resulting in modestly elevated tide levels around 0.5 to 0.75 feet above normal. Minor flooding appears unlikely, but can't be completely ruled out through Monday along vulnerable shoreline. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && SYNOPSIS...DHOF NEAR TERM...BRO/KJP SHORT TERM...KJP LONG TERM...DHOF AVIATION...DHOF/BRO/KJP MARINE...DHOF/KJP TIDES/COASTAL FLOODING...DHOF
Hazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 500 AM EDT Sun Aug 21 2022 ANZ530>543-DCZ001-MDZ008-011-013-014-016>018-504-506-508- VAZ052>057-220900- Chesapeake Bay north of Pooles Island MD- Chesapeake Bay from Pooles Island to Sandy Point MD- Chesapeake Bay from Sandy Point to North Beach MD- Chesapeake Bay from North Beach to Drum Point MD- Chesapeake Bay from Drum Point MD to Smith Point VA- Tidal Potomac from Key Bridge to Indian Head MD- Tidal Potomac from Indian Head to Cobb Island MD- Tidal Potomac from Cobb Island MD to Smith Point VA- Patapsco River including Baltimore Harbor- Chester River to Queenstown MD-Eastern Bay- Choptank River to Cambridge MD and the Little Choptank River- Patuxent River to Broomes Island MD- Tangier Sound and the inland waters surrounding Bloodsworth Island-District of Columbia-Cecil-Southern Baltimore- Prince Georges-Anne Arundel-Charles-St. Marys-Calvert- Central and Southeast Montgomery-Central and Southeast Howard- Southeast Harford-Prince William/Manassas/Manassas Park-Fairfax- Arlington/Falls Church/Alexandria-Stafford-Spotsylvania- King George- 500 AM EDT Sun Aug 21 2022 This Hazardous Weather Outlook is for the Maryland portion of the Chesapeake Bay, Tidal Potomac River, and I-95 corridor through central Maryland, northern Virginia, and District of Columbia. .DAY ONE...Today and Tonight Showers and scattered to numerous thunderstorms are expected late this afternoon into tonight. Some of the storms could produce heavy rainfall resulting in isolated instances of flooding. .DAYS TWO THROUGH SEVEN...Monday through Saturday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. MDZ003>006-503-505-507-VAZ025>031-036>040-050-051-501-502-505>508- WVZ050>053-055-220900- Washington-Frederick MD-Carroll-Northern Baltimore- Northwest Montgomery-Northwest Howard-Northwest Harford-Augusta- Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke-Nelson- Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper- Northern Fauquier-Southern Fauquier-Western Loudoun- Eastern Loudoun-Northern Virginia Blue Ridge- Central Virginia Blue Ridge-Hampshire-Morgan-Berkeley-Jefferson- Hardy- 500 AM EDT Sun Aug 21 2022 This Hazardous Weather Outlook is for portions of eastern West Virginia, northern and central Virginia, and central and western Maryland. .DAY ONE...Today and Tonight Showers and scattered to numerous thunderstorms are expected this afternoon through this evening. Some of the storms could produce heavy rainfall resulting in isolated instances of flooding. .DAYS TWO THROUGH SEVEN...Monday through Saturday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. MDZ001-501-502-VAZ503-504-WVZ501>506-220900- Garrett-Extreme Western Allegany-Central and Eastern Allegany- Western Highland-Eastern Highland-Western Grant-Eastern Grant- Western Mineral-Eastern Mineral-Western Pendleton- Eastern Pendleton- 500 AM EDT Sun Aug 21 2022 This Hazardous Weather Outlook is for the Allegheny Front counties in western Maryland, eastern West Virginia, and Highland County Virginia. .DAY ONE...Today and Tonight Showers and scattered to numerous thunderstorms are expected through this evening. Some of the storms could produce heavy rainfall resulting in isolated instances of flooding. .DAYS TWO THROUGH SEVEN...Monday through Saturday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. DHOF
The Sterling radar (KLWX), 158 km away, was scanning. The volume nearest the first event began at 14:43 UTC.
3 flood, 3 flash flood. Local standard time, as filed.
There was a report of two feet of water over a road at the Kate Collins Middle School.
There were multiple reports of flooding along Front Street.
Flooding was reported on University Avenue near Emmet Street. The road was blocked off by local city personnel.
Glade Road was caved in where Buffalo Creek Stream intersections the road north of the James River Road. A car was also stuck in flood waters near the caved in portion of the road.
Water was flowing over Route 29 around Town Creek.
Water was about 1 foot deep flowing over roads around Roseland. Cattle were stranded in flood waters as well.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Virginia in 2022Every state in 2022This day in weather historyWarnings in Virginia, August 2022
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1042771, 1042767, 1042772, 1042769, 1042768, 1042770.