A disturbance (the remnant of convection from the day before over the Tennessee River Valley) triggered a few supercells and line segments from eastern West Virginia into the Washington/Baltimore metro areas. This lead to some isolated instances of flooding in parts of MD.
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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 disturbance (the remnant of convection from the day before over the Tennessee River Valley) triggered a few supercells and line segments from eastern West Virginia into the Washington/Baltimore metro areas. This lead to some isolated instances of flooding in parts of MD.
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 3, 1:46 PM EST, 2 hours 56 minutes earlier.
Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 246 PM EDT Thu Sep 3 2020 .SYNOPSIS... A surface trough will linger across the area through this evening before a strong cold front crosses the area late Friday. High pressure will build over the area for the Labor Day weekend. && .NEAR TERM /THROUGH TONIGHT/... Showers are moving west-southwest to east-northeast across western Maryland and eastern West Virginia. No thunderstorms yet. I stress yet. Over the next hour or two, we should see a ramp up of strong to severe thunderstorms along I-81 and north of I-66 then immediately east closer to the metro area. Isolated supercells ahead of more organized convection could spawn a tornado or two. If not tornadoes, watch out for damaging winds and heavy rainfall. These thunderstorms will linger into early evening in the metro areas prior to pushing into southern Maryland thereafter. Although flooding concerns are low due to rapid movement of thunderstorms, a few thunderstorms could produce torrential rainfall that could lead to isolated incidences of flash flooding. The highest risk of encountering damaging winds and/or tornado along with flooding rainfall would be northeast Maryland. While temperatures will be in the upper 80s to lower 90s, the heat indice values could approach 100 degrees late this afternoon. Heat indice values could be closer to 105 in parts of east-central Virginia Tonight should be fairly quiet, with lows in the 60s and 70s after the convection makes its way into the Delmarva area. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... A quick moving cold front will move across our area on Friday. A few showers are possible ahead of it, especially over our higher elevations and our southern zones, where it will have weak mid level energy support and higher dew points. Instability will be around 1000 J/kg with 40 knots shear, so an isolated storm could develop with little impacts, especially in eastern Virginia and southern Maryland. High pressure will build into our area Friday night and will remain in control through Saturday night. Dry and cooler air mass will build over us. High temperatures on Saturday will be in the upper 70s and near 80. Low temperatures on Friday and Saturday night will drop into the 50s and 60s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... On Sunday, surface ridging along much of the Eastern Seaboard will remain in place although pressures should come down a bit as the ridge slowly edges eastward. This affords another day of seasonal temperatures along with lower dew points which stay in the mid/upper 50s. Heading into Labor Day, an upper ridge anchoring the western Atlantic is forecast to shift westward toward the coast. The building of mid-level heights will bring temperatures up a bit while conditions becoming noticeably more humid. Uncertainties loom during the early to middle portion of next week given global ensembles diverge on the pattern, most notably upstream. The conclusion of the holiday weekend will be dry with the potential return of precipitation to the forecast by as early as Tuesday. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... An upper level disturbance will spawn strong to severe thunderstorms across the terminals late this afternoon and early evening.. SubVFR conditions will be temporary due to lower cigs. VFR conditions return Thursday night and into Saturday night with quieter weather. A few showers are possible Friday afternoon, especially near CHO, with minimal impacts. No significant weather expected through Labor Day. && .MARINE... Winds remain below Small Craft Advisory criteria through Friday. Winds will increase behind a front Friday night and a Small Craft Advisory may be needed over portions of the waters. Winds will recede below criteria Saturday into Saturday night. Thunderstorms are expected to move across the waters this afternoon into the evening. Special Marine Warnings may be needed. Waterspouts cannot be ruled out. Slight increase in southeasterly winds by Labor Day, up to 12 knots. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...BRO AVIATION...KLW/BRO MARINE...KLW/BRO
Hazardous Weather Outlook National Weather Service Baltimore MD/Washington DC 351 PM EDT Thu Sep 3 2020 ANZ530>543-DCZ001-MDZ011-013-014-016>018-508-VAZ052>057-042000- 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-Southern Baltimore-Prince Georges- Anne Arundel-Charles-St. Marys-Calvert-Southeast Harford- Prince William/Manassas/Manassas Park-Fairfax- Arlington/Falls Church/Alexandria-Stafford-Spotsylvania- King George- 351 PM EDT Thu Sep 3 2020 This Hazardous Weather Outlook is for the Maryland portion of the Chesapeake Bay, Tidal Potomac River, and adjacent counties in central Maryland and northern Virginia as well as the District of Columbia. .DAY ONE...This Afternoon and Tonight Scattered severe thunderstorms with damaging wind gusts and isolated tornadoes are possible this afternoon into this evening. The best chance of severe weather is between 4 PM and 9 PM EDT. The risk is highest for areas along and north of U.S Highway 50. Scattered instances of flash flooding are possible in the District of Columbia, northeast Maryland, and portions of northeast Virginia. A Tornado Watch has been issued for the area until 10 pm this evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed today. MDZ003>006-501>507-VAZ025>031-036>040-050-051-501>508-WVZ050>053- 055-501>506-042000- Washington-Frederick MD-Carroll-Northern Baltimore- Extreme Western Allegany-Central and Eastern Allegany- Northwest Montgomery-Central and Southeast Montgomery- Northwest Howard-Central and Southeast Howard-Northwest Harford- Augusta-Rockingham-Shenandoah-Frederick VA-Page-Warren-Clarke- Nelson-Albemarle-Greene-Madison-Rappahannock-Orange-Culpeper- Northern Fauquier-Southern Fauquier-Western Highland- Eastern Highland-Western Loudoun-Eastern Loudoun- Northern Virginia Blue Ridge-Central Virginia Blue Ridge- Hampshire-Morgan-Berkeley-Jefferson-Hardy-Western Grant- Eastern Grant-Western Mineral-Eastern Mineral-Western Pendleton- Eastern Pendleton- 351 PM EDT Thu Sep 3 2020 This Hazardous Weather Outlook is for eastern West Virginia, northern and central Virginia, and central and western Maryland with the exception of Garrett County. .DAY ONE...This Afternoon and Tonight Isolated to scattered severe thunderstorms with damaging wind gusts and isolated tornadoes are possible this afternoon into this evening. The best chance of severe weather is between 1 PM and 9 PM EDT. The risk is highest for areas along and north of U.S. Highway 50. Scattered instances of flash flooding are also possible in portions of central Maryland. A Tornado Watch is out for a large part of the area until 10 pm this evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed this afternoon.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
457 PM EDT THU SEP 03 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0445 PM TSTM WND GST 1 ENE WASHINGTON GROVE 39.14N 77.16W
09/03/2020 M58 MPH MONTGOMERY MD MESONET
&&
EVENT NUMBER LWX2002367
DHPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
522 PM EDT THU SEP 03 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0454 PM TSTM WND DMG 1 E ROCKVILLE 39.08N 77.13W
09/03/2020 MONTGOMERY MD EMERGENCY MNGR
LARGE BRANCHES CAUSED POWER WIRES TO COME DOWN ON
WOODBURN ROAD NEAR MAPLE AVE.
&&
EVENT NUMBER LWX2002368
JMGThe Sterling radar (KLWX), 35 km away, was scanning. The volume nearest the first event began at 21:39 UTC.
12 flood, 1 flash flood. Local standard time, as filed.
Norbeck Rd. impassable between Bauer Rd. and Baltimore Rd.
The water level rapidly rose above flood stage of 5.5 feet within 40 minutes. The water level crested at 6.14 feet at 5:10 PM EST. Sligo Creek Parkway was flooded near the gauge location just north of Maple Avenue.
Reports of flooded roadway at the intersection of Tinker Rd.
Reports of flooded roadway at the intersection of Tinker Rd.
Flooding at the intersection of Orems Rd. and Rossville Blvd.
The water level rose above the flood stage along the Middle River. The water level crested at 10.89 feet at 5:08 PM EST. Wilsons Point Road was flooded with at least six inches of water flowing over the road in spots.
Beach Dr. closed due to flooding between Grosvenor Ln. and Stoneybrook Dr.
Macarthur Blvd. impassable due to flooding.
Mayo Rd. closed due to flooding.
The water level along the Northeast Branch of the Anacostia River in Riverdale rose above flood stage. The water level crested at 8.1 feet at 7:05 PM EST. The northeast branch trail was flooded in spots.
Defense Hwy. closed due to flooding near Saint Stephens Church Rd.
Central Ave. closed due to flooding at Beards Creek.
The water level at Upper Marlboro rose above flood stage, and it crested at 11.86 feet at 12:15 PM EST. The Water Street Bridge was covered by water.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2020Every state in 2020This day in weather historyWarnings in Maryland, September 2020
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: 921030, 920485, 921032, 921033, 921036, 922007, 921039, 921043, 921044, 922010, 921045, 921047, 922008.