A slow moving cold front approached the area on the 22nd before passing through on the 23rd. A deep southerly flow allowed for tropical moisture to move into the area ahead of the boundary.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LWX wrote it up.
A slow moving cold front approached the area on the 22nd before passing through on the 23rd. A deep southerly flow allowed for tropical moisture to move into the area ahead of the boundary. This led to heavy rainfall as the cold front approached, and several instances of flooding along with isolated instances of flash flooding occurred.
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 Sep 22, 3:01 AM EST, 2 hours 21 minutes earlier.
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
401 AM EDT Wed Sep 22 2021
.SYNOPSIS...
An upper-level disturbance will pass over the region this
morning. A strong cold front will then move across the region
later today through Thursday. Canadian high pressure will then
build overhead late this week into the weekend.
&&
.NEAR TERM /THROUGH THURSDAY/...
Current water vapor satellite depicts a weak upper-level
disturbance over central VA moving towards the northeast.
Additionally, a much stronger upper-level trough is digging into
the Ohio Valley and taking on more of a negative tile. This is
resulting in an abundance of moisture across the region at this
time, with moderate to heavy showers across central and southern
VA. The heaviest of precipitation has generally been to our
south for the time being, but that will change in the next
several hours, as the weak upper-level disturbance passes
overhead. Blended TPW and RAP mesoanalysis depict rich PWATS in
excess of 2" advecting into our southwestern zones. There will
be a significant upslope component into the Blue Ridge Mountains
with training convection due to strong unidirectional flow.
Already seeing some impressive rainfall amounts to our south, so
expect to see an uptick in rainfall as we get further into this
morning.
This activity will move towards the north through the early
afternoon, before leaving a brief "lull" in its wake. I use
quotes there because there may not really be much of a dry
period. Recent trends have been a little more bullish in terms
of CAPE across our SW zones, developing another round of
thunderstorms down that way this afternoon ahead of the main
cold front, which will be on our doorstep by mid-afternoon. With
the surface low occluding off to the northwest, the cold front
will progress across the region rather slowly Wednesday late in
the afternoon through Thursday afternoon, before clearing the
region by Thursday evening.
As far as hazards are concerned, the first to be concerned with
will be the risk for flooding rainfall, especially west of the
Blue Ridge. Current forecast depicts 3-5 inches in these areas
with isolated higher amounts of 6-8 inches across the ridges
where higher rainfall rates are expected due to orographic
enhancement. Severe weather is also a threat this afternoon
through Thursday afternoon. Could see a sneaky severe threat
across our southwestern zones this afternoon with abundant
moisture and shear and the uptick in CAPE observed in some of
the latest guidance. This would be ahead of the main cold front,
and gusty winds and an isolated tornado can't be ruled out with
this round of convection. Then of course the main line comes
through later this afternoon/evening through Thursday. This is
associated with the cold front itself and will be the higher
threat for severe weather. Would likely see a bit of a downtick
in severe threat overnight, but Thursday could get quite
interesting across central and northeast MD should we tap into
the higher instability (up to 1000 J/kg) depicted in some of
the guidance. Damaging winds and an isolated tornado are the
primary threats with this round as well.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As mentioned previously, the cold front is expected to clear the
region Thursday night. In its wake, much cooler temperatures
are expected overnight, with lows dipping into the upper 40s to
mid 50s (with lower values closer to 40 out west).
Dry and seasonably cool on Friday with highs in the low to mid
70s as high pressure builds towards the region. This will
continue into Friday night as well, with temps even a touch
cooler than Thursday night.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
An amplified but fairly progressive pattern is expected through the
extended forecast period. Surface high pressure will be situated
southwest of the area Saturday, which should provide dry weather
much of the day along with slightly below normal temperatures. A
shortwave trough and accompanying weak surface front will approach
Saturday evening and cross Saturday night. Moisture will already be
limited with the front, and low level westerly (downsloping) flow
should keep any minimal shower chance near and west of the Allegheny
Front.
Surface high pressure will expand across the area Sunday and Monday.
Dry weather is expected with seasonable temperatures, with Monday
slightly warmer due to return flow.
Model solutions diverge by Tuesday in handling the timing and
amplitude of the next shortwave trough. The forecast remains dry now
due to the disparate ensemble solutions, although the 00Z guidance
suite indicates a trend toward a chance of showers and perhaps even
thunderstorms.
&&
.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Low-end MVFR to IFR CIGs are overspreading the region at this
time. Showers over KCHO and KMRB at this time as well. CIGs
improve somewhat to MVFR this afternoon ahead of a strong cold
front pushing towards the area. The rest of terminals will get
into the showers by later today and continuing into Thursday.
Expect gusty winds today at eastern terminals. Strong frontal
passage expected Thursday morning with shifting winds from NW.
VFR conditions return for Thursday night through Friday as high
pressure builds towards the area.
VFR conditions expected this weekend. Weak frontal passage will
likely result in a wind shift from south to west Saturday night.
&&
.MARINE...
Strengthening SSE winds today with solid SCA expected and Gale
gusts expected Wed afternoon and night. Gradient winds begin to
diminish after 15Z Thu but with SCA conditions persisting. As
the cold front pushes through Thursday, could see some SMWs
being needed as gusty winds will be possible in thunderstorms
along the boundary.
NW wind gusts of 20-25 kts are possible behind the cold front on
Friday. The wind should become lighter Friday night.
Winds will become southerly on Saturday but then shift to the west
Saturday night as a weak front passes. Marginal SCA conditions are
possible Saturday night into Sunday morning.
&&
.TIDES/COASTAL FLOODING...
Anomalies haven't increased much as of early this morning. Am only
expecting minor flooding at DC SW Waterfront this morning, although
Annapolis will be close.
Water levels will likely increase dramatically later today and
tonight as southerly winds strengthen. There's some uncertainty with
just how high anomalies will be, as model guidance can be too
aggressive in these regimes. However, fairly widespread minor
flooding is possible later today through Thursday morning. Have
issued a Coast Flood Watch for Annapolis since guidance indicates
close to moderate flood levels.
There's also some uncertainty on how quickly water levels decrease
on Thursday, which will be dependent on a wind shift associated with
a cold front.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory from 7 AM this morning to midnight EDT
tonight for DCZ001.
MD...Flash Flood Watch from 8 AM EDT this morning through Thursday
morning for MDZ001-003-004-501-502.
Coastal Flood Watch from 3 PM EDT this afternoon through
Thursday morning for MDZ014.
Coastal Flood Advisory until 6 AM EDT early this morning for
MDZ017.
VA...Flash Flood Watch through Thursday morning for VAZ025>027-029-
036>038-503-504-507-508.
Flash Flood Watch from 8 AM EDT this morning through Thursday
morning for VAZ028-030-031-039-040-501-505.
WV...Flash Flood Watch through Thursday morning for WVZ055-501-502-
505-506.
Flash Flood Watch from 8 AM EDT this morning through Thursday
morning for WVZ050>053-503-504.
MARINE...Small Craft Advisory until noon EDT today for ANZ531>533-
539>542.
Small Craft Advisory from 4 AM to 6 PM EDT Thursday for
ANZ531>534-537-539>543.
Gale Warning from noon today to 4 AM EDT Thursday for
ANZ531>534-537-539>543.
Small Craft Advisory until noon EDT today for ANZ534-537-543.
Small Craft Advisory until 6 PM EDT Thursday for ANZ530-535-
538.
Small Craft Advisory until 6 PM EDT Thursday for ANZ536.
&&
SYNOPSIS...CJL
NEAR TERM...CJL
SHORT TERM...CJL
LONG TERM...ADS
AVIATION...ADS/CJL
MARINE...ADS/CJL
TIDES/COASTAL FLOODING...ADSHazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 515 AM EDT Wed Sep 22 2021 ANZ530>543-DCZ001-MDZ008-011-013-014-016>018-504-506-508- VAZ052>057-230915- 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- 515 AM EDT Wed Sep 22 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...Today and Tonight A Gale Warning is in effect this afternoon through much of tonight for the lower tidal Potomac River, and portions of the Chesapeake Bay and adjoining estuaries between Smith Point and Pooles Island. A Coastal Flood Watch goes into effect for Anne Arundel County at 3 PM for the potential of moderate coastal flooding. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday A Coastal Flood Watch remains in effect for Anne Arundel County through Thursday morning. Severe thunderstorms are possible Thursday. The main threats are damaging wind gusts or an isolated tornado, though a few instances of flooding can't be ruled out. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed Thursday. MDZ003>006-503-505-507-VAZ025>031-036>040-050-051-501-502-505>508- WVZ050>053-055-230915- 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- 515 AM EDT Wed Sep 22 2021 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 A Flash Flood Watch is in effect for areas along and west of US Route 15 through tonight. Severe thunderstorms are possible late this afternoon and tonight. The main threats are damaging wind gusts or an isolated tornado. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday Severe thunderstorms are possible Thursday east of the Blue Ridge and Catoctin Mountains. The main threats are damaging wind gusts or an isolated tornado. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this afternoon into Thursday. MDZ001-501-502-VAZ503-504-WVZ501>506-230915- Garrett-Extreme Western Allegany-Central and Eastern Allegany- Western Highland-Eastern Highland-Western Grant-Eastern Grant- Western Mineral-Eastern Mineral-Western Pendleton- Eastern Pendleton- 515 AM EDT Wed Sep 22 2021 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 A Flash Flood Watch is in effect for the entire outlook area through tonight. A River Flood Watch is in effect for the South Branch Potomac River at Franklin West Virginia. Severe thunderstorms are possible this afternoon into tonight. The main threats are damaging wind gusts or an isolated tornado. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed later today.
The Sterling radar (KLWX), 74 km away, was scanning. The volume nearest the first event began at 10:22 UTC.
63 flood, 4 flash flood. Local standard time, as filed.
The water level along the Big Pipe Creek at Bruceville rose above flood stage, cresting at 11.33 feet at 9:45 AM on the 23rd of September. Keysville-Bruceville Road was flooded.
Road closures due to flooding starting to be reported in the Brunswick, Jefferson, and Knoxville areas.
Road closure due to flooding in the Rocky Ridge area.
Hill Road between Coppermine Road and Renner Road is closed due to high water.
MD 194 at Cash Smith Road was closed due to high water.
There was a swift water rescue near the 8900 Block of Jones Road in Libertytown.
MD-75 at Coppermine Road was closed due to high water.
Sams Creek Road was closed due to flooding at Sams Creek between MD-31 New Windsor Road and Oak Orchard Road.
Claybaugh Road was closed due to flooding at Little Pipe Creek.
Hill Road was closed due to flooding between Coppermine Road and Renner Road.
Hiney Road was closed due to flooding between Legore Road and Haughs Church Road.
Roddy Road was closed due to flooding at Owen's Creek.
Jones' Road was blocked by high water near South Street.
High water blocks MD-26 (Main Street) at Trammel's Valley.
The Little Antietam Creek was flowing across Leitersburg Smithsburg Road, closing the road.
A swift water rescue took place in the 9900 Block of Daysville Road at Cabbage Run.
The stream gauge on Big Pipe Creek at Bruceville reached flood stage.
High water blocks MD-355 Urbana Pike near Doctor Perry Road.
Devilbliss Bridge Road was blocked by high water near MD-194 Woodsboro Pike.
MD-31 New Windsor Road was blocked by high water near Bessie Clemson Road.
Water rescue for a vehicle stranded in high water near Beach Drive and Connecticut Avenue.
Bretheren Church Road was closed due to flooding at Catoctin Creek.
Orndoff Road was closed due to flooding near Old Frederick Road.
Water Street Road was closed due to flooding by Harp Road.
Detrick Road was closed due to flooding near South Fork Bens Branch.
Lime Plant Road was closed due to flooding at North Fork Bens Branch.
Stauffer Road was closed due to flooding near Water Street Road.
Crum Road was closed due to flooding near Stauffer Road.
Old Frederick Road was closed due to flooding near Old Mill Road.
Jesse Smith Road was closed due to flooding at South Fork Bens Branch.
Annandale Road was closed due to flooding near Toms Creek.
Gas House Pike was closed due to flooding near Central Church Road.
The 11800 Block of Beaver Dam Road was blocked by high water.
Rock Creek out of its banks flooding Beach Drive near Cedar Lane. Roadway being closed.
Several roads were blocked by high water in Westminster.
Several roads were blocked by high water in Winfield .
Several roads were blocked by high water in Mount Airy .
Several roads closed due to high water in/near Bethesda.
MD-84 Baust Church Road was closed due to flooding at MD-382 Old Taneytown Road.
The water level along the Monocacy River at Bridgeport rose above flood stage, cresting at 16.55 feet at 1:30 PM EST on the 23rd of September. Fields and yards were flooded near Bridgeport and Baptist Road was also flooded.
MD-5 Leonardtown Road was closed due to flooding at Post Office Road.
The stream gauge on the Monocacy River at Bridgeport reached flood stage.
MD-238 Maddox Road was closed due to flooding south of Hurry Road.
The water level along the Seneca Creek at Dawsonville rose above flood stage, cresting at 7.67 feet at 8:40 AM EST on the 23rd of September. Portions of the Seneca Creek Greenway were flooded and a small portion of Berryville Road west of Darnestown Road was flooded.
The stream gauge on Seneca Creek at Dawsonville reached flood stage.
About a half dozen roads closed for high water.
Sligo Creek Parkway was closed due to flooding between MD-320 Piney Branch Road and Maple Avenue.
The water level rose above flood stage along the Patuxent River in Unity, cresting at 8.54 feet at 11:25 AM EST on the 23rd. The parking lot for the Patuxent River State Park at Maryland Route 97 was flooded.
The stream gauge on the Patuxent River at Unity reached flood stage.
MD-7 Philadelphia Road is closed due to flooding near MD-136 Calvary Road.
MD-22 Churchville Road was blocked by high water at Aldino Stepeny Road.
High water on Westbound I-70/US-40 Baltimore National Pike at Mile Marker 64.0.
US-40 Pulaski Highway is closed due to flooding between Locust Lane and Robin Hood Road.
New Bridge Road closed at Horseshoe Road due to Octoraro Creek flowing onto the intersection/bridge.
Old Battle Grove Road was closed due to flooding near North Point Road.
Grace Road was closed due to flooding near Alice Avenue.
MD-623 Castleton Road was closed due to flooding at Peddler Run near Glen Cove.
Multiple vehicles were stranded in 6 to 12 inches of water flowing across US-40 (South Philadelphia Boulevard) near Old Philadelphia Road.
The water level rose above flood stage of 7 feet, cresting at 7.46 feet on September 23rd at 12:00 PM EST. Portions of Upper Glencoe Road and Lower Glencoe Road were flooded.
The stream gauge on Gunpowder Falls at Glencoe reached flood stage.
Old Fort Road was closed around Fort Washington Road due to high water.
A car was stuck in high water in Bladensburg.
The water level rose above flood stage, cresting at 19.03 feet at 4:45 AM on the 23rd of September. Significant lowland flooding occurred along the river, with backwater flooding also occurring. Numerous roads were closed. Water reached the parking lot at Gambrill Mill along the Monocacy Battlefield. Backwater flooding from Carroll Creek also approached the underside of the bridge leading to the Frederick city wastewater treatment plant.
Much of Pinecliff Park and Rivermist Park were flooded. Buckeystown Community Park was also flooded.
The stream gauge on the Monocacy River at Frederick reached flood stage.
The water level along the Monocacy River at Frederick (FRMM2) rose above moderate flood stage, cresting at 22.59 feet at 1:45 AM EST on the 24th of September.
The stream gauge on the Monocacy River above Frederick reached flood stage.
The water level rose above flood stage, cresting at 16.39 feet at 3:35 PM EST on the 23rd. Water covered a portion of River Road in the Patapsco Valley State Park. Large portions of the park were flooded near the playground off Gunn Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2021Every state in 2021This day in weather historyWarnings in Maryland, September 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: 986645, 986372, 986373, 986374, 985690, 985691, 985692, 986375, 986376, 986377, 986378, 986389, 986390, 986392, 986393, 985693, 986394, 986397, 986414, 986415, 986400, 986416, 986417, 986418, 986419, 986420, 986424, 986429, 986431, 986433, 986434, 986578, 986579, 986401, 986582, 986585, 986588, 986412, 986591, 986655, and more.