An isolated thunderstorm produced flooding in Greene County, VA.
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The episode as NWS LWX wrote it up.
An isolated thunderstorm produced flooding in Greene County, VA.
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, 8:00 PM EST, 3 hours 25 minutes earlier.
Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 900 PM EDT Sat Aug 21 2021 .SYNOPSIS... An upper-level low will remain overhead through the weekend, while Henri tracks northward toward Long Island/New England. High pressure will build in for the first half of the week before a cold front approaches from the north during the second half of the week. && .NEAR TERM /THROUGH SUNDAY/... 9:00 PM UPDATE: Current satellite observations depict an upper low directly over the forecast area, particularly over our western zones. This has re-invigorated convection over the higher terrain, even now in the absence of daytime heating. A few storms have gotten fairly tall, but have failed to become severe thus far. The bigger concern is going to be for some isolated instances of flooding/flash flooding, as storms struggle to move much in the absence of significant steering flow. Do expect this to gradually taper off over the next few hours however, as stabilization continues. So, will maintain an isolated severe/flash flood threat until radar activity tapers off. PREVIOUS DISCUSSION: As we move into the overnight hours, attention will turn to our north, where an inverted surface trough is expected to develop over PA/NJ to the northwest of Henri/ahead of the upper low overhead. Model guidance indicates that a very heavy band of precipitation may form within this inverted trough, but thankfully CAM guidance has also been consistent run to run in keeping this heavier precipitation just to the north and east of our forecast area. However, this feature does bear watching as we move through the rest of the day into tonight, since it could potentially impact northeast MD if its location were to trend further southwest over time. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... 9:00 PM UPDATE: With the latest runs of the HRRR, now including the 18z extended run, not much has changed in regards to our forecast for tomorrow. Still far too much uncertainty at this point to know for sure how much rain northeast Maryland sees tomorrow. The 18z run throws a spiral band down through northeast MD early tomorrow morning, then brings in wrap-around precip late tomorrow night. Should this occur, we would likely have some flooding issues, albeit isolated outside of the Baltimore metro. Will have to monitor closely as the overnight runs come in to see if some consensus is formed on the evolution of things tomorrow regarding Henri. Think as the 00z guidance trickles in, perhaps a decision can be made on any flooding headlines. PREVIOUS DISCUSSION: The aforementioned upper low will continue to reside overhead during the day tomorrow. Meanwhile, Henri will continue to track toward the north, likely making landfall on Long Island some time tomorrow afternoon. Exactly how Henri interacts with the upper low will have a strong influence on our forecast for tomorrow, and an atypical amount of spread exists in the forecast for tomorrow afternoon into tomorrow night, especially across northeastern MD. Some members of the 12z HREF (most notably the HRRR and WRF-ARW members) draw Henri much further south than other model guidance, backing heavy rain into northeastern MD by tomorrow evening. If this type of scenario were to play out, some localized instances of flooding can't be ruled out. Thankfully, flash flood guidance is relatively high over northeastern MD outside of Baltimore, so we may avoid hydro issues as long as the heaviest rain stays out of Baltimore. These HRRR and WRF-ARW solutions are outliers at the moment, so it is very possible that the entire forecast area avoids heavier rain, with just some lighter rain across northern MD tomorrow afternoon into tomorrow night. Elsewhere, a stray shower or thunderstorm can't be ruled out tomorrow afternoon or evening, but areal coverage of storms isn't expected to be high and the storms aren't expected to be intense. Any precipitation associated with Henri should exit off to our north and east by daybreak Monday. The upper low will also depart off to our north and east during the day Monday, but a warm and humid airmass will still remain in place in its wake. As a result, a stray afternoon or evening thunderstorm can't be ruled out in response to daytime heating. With limited instability and weak flow, any storms that do form aren't expected to lead to any hazardous weather. Highs on Monday will return to near normal, with highs in the upper 80s for most. && .LONG TERM /TUESDAY THROUGH SATURDAY/... High pressure returns to the region for the bulk of the week, with hot and humid conditions and spotty afternoon thunderstorms. Hottest and driest day looks likely to be Tuesday in the wake of Henri with best compressional heating as the system moves away and high pressure builds in. This wanes Wednesday and Thursday as high pressure, initially just to our west, shifts east and we start to get a stronger flow of moist tropical air back northward across the region. By Friday into Saturday, we'll be watching a front approaching from the north, which may start to focus the storm development Friday, then may stall in the area Saturday. Still lots of uncertainty with this, but overall looks like a stormier and cooling trend as we head into next weekend. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... Prevailing VFR conditions are expected through Monday. Thunderstorms will be possible each afternoon, but areal coverage of storms isn't expected to be high. A steadier period of rain associated with the outer fringe of Henri may potentially work into MTN or BWI tomorrow evening, but confidence in this occurring remains low. Winds will be light out of the east or north today through tonight, before becoming light out of the west to northwest tomorrow through Monday. Generally VFR Tuesday through Thursday under high pressure. Main concern is for patchy early morning fog and isolated to scattered afternoon/early evening thunderstorms. Best risk of both will be at MRB and CHO. The risk likely is lowest on Tuesday with a gradual increase in chances through Thursday. && .MARINE... Sub-SCA level winds are expected through Monday. Winds will be light out of either the east or north today, before becoming light out of the west to northwest tomorrow and Monday. An MWS may be needed this afternoon if a storm were to move over the waters. Light winds likely prevail over Tuesday thru Thursday under high pressure. Only concern would be for an isolated thunderstorm reaching the waters. The risk likely is lowest on Tuesday with a gradual increase in chances through Thursday. && .TIDES/COASTAL FLOODING... Latest guidance has continued to keep tidal anomalies lower. Most sites with the exception of DC Waterfront and Annapolis will remain below action stage over the next few days. Otherwise, not anticipating any minor tidal flooding issues over the next few days. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && SYNOPSIS...KJP NEAR TERM...CJL/KJP SHORT TERM...CJL/KJP LONG TERM...RCM AVIATION...RCM/KJP MARINE...RCM/KJP TIDES/COASTAL FLOODING...BRO
Hazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 1003 PM EDT Sat Aug 21 2021 ANZ530>543-DCZ001-MDZ008-011-013-014-016>018-504-506-508- VAZ052>057-230215- 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- 1003 PM EDT Sat Aug 21 2021 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...Tonight No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday Isolated instances of flash flooding are possible Sunday and Sunday night in association with Henri, particularly near and northeast of Baltimore. .SPOTTER INFORMATION STATEMENT... Spotter activation may be necessary today. MDZ003>006-503-505-507-VAZ025>031-036>040-050-051-501-502-505>508- WVZ050>053-055-230215- 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- 1003 PM EDT Sat Aug 21 2021 This Hazardous Weather Outlook is for portions of eastern West Virginia, northern and central Virginia, and central and western Maryland. .DAY ONE...Tonight Scattered slow moving storms could lead to isolated instances of flash flooding over the next couple of hours. An isolated severe thunderstorm is also possible through this evening, with damaging winds being the primary threat. .DAYS TWO THROUGH SEVEN...Sunday through Friday Isolated instances of flash flooding are possible Sunday and Sunday night in association with Henri, particularly near and northeast of Baltimore. .SPOTTER INFORMATION STATEMENT... Spotter activation may be necessary today. MDZ001-501-502-VAZ503-504-WVZ501>506-230215- Garrett-Extreme Western Allegany-Central and Eastern Allegany- Western Highland-Eastern Highland-Western Grant-Eastern Grant- Western Mineral-Eastern Mineral-Western Pendleton- Eastern Pendleton- 1003 PM EDT Sat Aug 21 2021 This Hazardous Weather Outlook is for the Allegheny Front counties in western Maryland, eastern West Virginia, and Highland County Virginia. .DAY ONE...Tonight Scattered slow moving storms could lead to isolated instances of flash flooding over the next couple of hours. An isolated severe thunderstorm is also possible through this evening, with damaging winds being the primary threat. .DAYS TWO THROUGH SEVEN...Sunday through Friday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation not expected at this time. CJL
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
N. Ridge Way bridge over Standardsville Run closed due to flooding.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Virginia in 2021Every state in 2021This day in weather historyWarnings in Virginia, August 2021
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: 980892.