A boundary remained overhead on the 30th of July. Hot and humid conditions led to an unstable atmosphere. The instability along with the boundary caused a few severe thunderstorms to develop. Thunderstorms merged across Montgomery, Howard and Baltimore counties and led very heavy rainfall that led to flash flooding. Catastrophic flash flooding occurred in Ellicott City, MD the night of July 30th.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 22:54:00 to 31-JUL-16 06:47:00 (EST-5)
Location: OAKLAND MILLS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Little Patuxent River at Guilford reached their flood stage of 11 feet. It peaked at 14.97 feet at 1:15 EST. Water covered the bridge at South Entrance Road and several trail brides also began to flood. Water approached US 29 in Columbia.

Flood in HOWARD, MARYLAND
From 30-JUL-16 21:45:00 to 31-JUL-16 08:36:00 (EST-5)
Location: SAVAGE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Little Patuxent River at Savage reached their flood stage of 10 feet. It peaked at 18.04 feet at 02:45 EST. Laurel Fort Meade Road was covered by water.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 20:13:00 to 31-JUL-16 00:11:00 (EST-5)
Location: UNITY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Patuxent River at Unity reached their flood stage of 8 feet. It peaked at 9.83 feet at 21:15 EST. The parking lot for the Patuxent River State Park at Maryland Route 97 began to flood.

Flash Flood in BALTIMORE, MARYLAND
From 30-JUL-16 19:46:00 to 30-JUL-16 21:01:00 (EST-5)
Location: MILFORD
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Scotts Level Branch at Rockdale reached their flood stage of 7 feet. It peaked at 7.83 feet at 20:20 EST. Water entered backyards of homes near the stream.

Flash Flood in BALTIMORE, MARYLAND
From 30-JUL-16 20:15:00 to 31-JUL-16 00:20:00 (EST-5)
Location: LOCHEARN
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Gwynn Falls reached their flood stage of 11 feet twice. It was flooding from 20:15 EST until 22:19 EST. It peaked at 11.48 feet at 21:15 EST. The second time it flooded was from 23:49 EST until 00:20 EST. It peaked at 11.07 feet at 00:00 EST. Queen Anne Road began to flood between Essex Road and Villa Nova Road.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 19:18:00 to 31-JUL-16 03:15:00 (EST-5)
Location: CLARKSBURG
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

There was 10 inches of flowing water near 22300 North Frederick Road. There was a person assisted from a car.

Flash Flood in BALTIMORE CITY (C), MARYLAND
From 30-JUL-16 20:13:00 to 30-JUL-16 23:00:00 (EST-5)
Location: WESTPORT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Gwynn Falls at Washington Boulevard reached their flood stage of 13 feet. It peaked at 17.72 feet at 21:05 EST. Water covered the bike path alongside the stream and approached the end of Berlin Street.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 19:44:00 to 31-JUL-16 03:15:00 (EST-5)
Location: DAVIS ARPT
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

There were multiple people rescued from a car by a boat near the 8900 block of Watkins Road.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 19:52:00 to 31-JUL-16 03:15:00 (EST-5)
Location: LAYTONSVILLE
Flood cause: Heavy Rain
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Five people were rescued from three cars near 5700 Sundown Road.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 19:53:00 to 31-JUL-16 03:15:00 (EST-5)
Location: LAYTONSVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

There was a road closed near the intersection of Woodfield Road and Churchill Downs Road due to a foot of water flowing across the road.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 19:53:00 to 31-JUL-16 03:15:00 (EST-5)
Location: BROOKEVILLE
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

There were two people rescued from a car by boat near 19800 Georgia Ave.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 20:16:00 to 31-JUL-16 03:15:00 (EST-5)
Location: PURDUM
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

There was about one foot deep of water flowing about 100 feet south of the intersection of Kings Valley Road and Kingstead Road.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 20:20:00 to 31-JUL-16 03:15:00 (EST-5)
Location: UNITY
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

There was eight inches of water flowing across the road near the interesection of Sundown Road and Zion Road. A person was rescued from a car near 22200 Zion Road.

Flash Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 20:22:00 to 31-JUL-16 03:15:00 (EST-5)
Location: CLARKSBURG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

North Frederick Road was closed in both direction at New Cut road near a bridge crossing over Little Seneca Creek.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 19:48:00 to 30-JUL-16 21:33:00 (EST-5)
Location: NORMANDY HGTS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on the Patapsco River at Hollofield reached their flood stage of 11 feet. It peaked at 14.05 feet at 20:30 EST. Hollofield Road began to flood.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 19:26:00 to 30-JUL-16 23:01:00 (EST-5)
Location: ELKRIDGE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on the Patapsco River at Catonsville reached their flood stage of 20 feet. It peaked at 27.14 at 20:15 EST. Significant flooding was occurring along the river.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 19:06:00 to 31-JUL-16 03:15:00 (EST-5)
Location: ELLICOTT CITY
Flood cause: Heavy Rain
Property damage: 22.40M
Crop damage: 0.00K
Reported by: NWS Storm Survey

The survey revealed clear signs of flooding both from the Patapsco River and from flash flooding within Ellicott City.  Signs of flooding, including damaged pavement, were observed as far up as the intersection of Rogers Avenue and Frederick Road, where Hudson Branch came out of its banks. From this location, eyewitnesses reported seeing water not only in the creek, but moving swiftly down Main Street beginning just after dark.  The intersection of Rogers Avenue and Frederick Road is about 140 feet higher in elevation than the lower part of Old Town Ellicott City. Erosion was noted on both the street side and the creek side of homes along Main Street in a portion of the 8500 block.
The next signs of damage were in the 8300 block of Main Street, with damage again observed both on the creek/river side and the street side of Main Street.  The creek/river side is where the most vehicles were impacted, in Lot D.
In the 8200 block, surveys and surveillance footage show water anywhere from 6 inches to two feet inside buildings on Main Street along with substantial damage to sidewalks and infrastructure outside the buildings.
The most significant damage observed was near 8100 Main Street, where the street curves slightly. Video surveillance footage reviewed after the event clearly indicates that water from the Tiber River was flowing through buildings on the south side of Main Street in this area, toward the street.
Closer to the Patapsco, damage continued with water marks observed 6-8 feet high on and in most buildings. The force of the floodwaters swept away the iconic Ellicott City clock as well as the historical flood marker that was attached to the railroad bridge.

Flood in FREDERICK, MARYLAND
From 30-JUL-16 16:02:00 to 31-JUL-16 21:30:00 (EST-5)
Location: CATOCTIN FURNACE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Auburn Road was closed near to Baugher Road due to flooding.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 19:30:00 to 30-JUL-16 22:02:00 (EST-5)
Location: ELLICOTT CITY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on the Patapsco River at Ellicott City reached their flood stage of 124 feet. It peaked at 128.05 feet at 20:00 EST. Major flooding occurred across Old Town Ellicott City and became more significant due to local rainfall of about 6 inches of rain. Old Town Ellicott City experienced catastrophic damage from flooding.

Flash Flood in BALTIMORE, MARYLAND
From 30-JUL-16 20:12:00 to 30-JUL-16 20:53:00 (EST-5)
Location: CATONSVILLE MANOR
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge at Dead Run at Franklintown reached their flood stage of 10 feet. It peaked at 10.57 at 20:40 EST. Kernan Road began to flood including portions of Dead Run Park.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 19:55:00 to 31-JUL-16 00:31:00 (EST-5)
Location: ELKRIDGE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on the Patapsco River at Elkridge reached their flood stage of 15 feet. It peaked at 23.58 feet at 21:15 EST. Water began to approach structures, Washington Boulevard began to flood at the Elkridge/Halethorpe border, water covered the entrance park at Patapsco Valley State Park and a low spot near the end of Levering Avenue began to flood.

Flash Flood in BALTIMORE, MARYLAND
From 30-JUL-16 19:48:00 to 30-JUL-16 20:16:00 (EST-5)
Location: HALETHORPE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on East Branch Herbert Run reached their flood stage of 7 feet. It peaked at 8.13 feet at 19:55 EST. Water approached structures along the creek and approached the top of a culvert at Sulphur Spring Road.

Flood in CARROLL, MARYLAND
From 30-JUL-16 22:29:00 to 31-JUL-16 22:29:00 (EST-5)
Location: MAYBERRY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Mayberry and Bear Run roads were closed due to flooding.

Flood in MONTGOMERY, MARYLAND
From 30-JUL-16 18:48:00 to 30-JUL-16 20:02:00 (EST-5)
Location: BURDETTS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Ten Mile Creek in Boyds exceeded their 7 foot flood stage. The peak was 8.55 feet at 19:15 EST. Agricultural fields near Ten Mile Creek flooded.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 22:08:00 to 31-JUL-16 05:19:00 (EST-5)
Location: GUILFORD
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: River/Stream Gage

The stream gauge on Little Patuxent River at Allview reached their flood stage of 280 feet (elevation). It peaked at 284 feet at 00:15 EST. Carlinda Avenue began to flood at its lowest point.

Flash Flood in HOWARD, MARYLAND
From 30-JUL-16 18:52:00 to 30-JUL-16 20:30:00 (EST-5)
Location: BRINKLEIGH MANOR
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

Route 40 was closed at Route 29 in Ellicott City. There was a home at 3239 Brookmeade Road with high water marks about 2 feet high on the garage doors.