A cold front dropped southward across the region and interacted with modestly moist and unstable conditions. A humid boundary layer was in place as evidenced by surface dewpoints in the upper 60s to lower 70s. All of this worked to generate widespread thunderstorms mid-afternoon into the early evening over the Southern Tier. A cold front came through in pieces though with first a wind shift to the north noted as early as the early afternoon over Southern Tier, however lower dewpoints failed to arrive until late evening and overnight. Strong low level lapse rates were present, however shear was weak and the mean layer flow was only around 5 knots. The one hour flash flood guidance was about 1.5 inches across the Southern Tier. The storms that developed were very slow movers and flash flooding was observed in all three southern Tier counties. Storms that had stronger cores aloft produced isolated downbursts in southeastern Chautauqua County and southeastern Allegany County. Of interest, peak wind gusts with convection came from the east, which is a non-typical wind direction. This likely resulted in more wind damage to trees than normal for these cells.

Flash Flood in CHAUTAUQUA, NEW YORK
From 09-JUN-21 16:30:00 to 09-JUN-21 18:30:00 (EST-5)
Location: KIANTONE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

South Main Street Extension closed from Bacon Road to the Pennsylvania state line due to high water.

Flash Flood in CATTARAUGUS, NEW YORK
From 09-JUN-21 16:15:00 to 09-JUN-21 17:15:00 (EST-5)
Location: ELLICOTTVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Route 219 flooded and closed in front of the Dollar General.

Flash Flood in ALLEGANY, NEW YORK
From 09-JUN-21 16:25:00 to 09-JUN-21 17:00:00 (EST-5)
Location: WEST CLARKSVILLE
Flood cause: Heavy Rain
Property damage: 40.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water was pouring into four homes with at least four feet of water in each. The fire department was unable to successfully pump the water out for a time due to the rate of water coming into each home.

Thunderstorm Wind in ALLEGANY, NEW YORK
From 09-JUN-21 13:40:00 to 09-JUN-21 13:40:00 (EST-5)
Location: STANNARDS
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Multiple trees were downed in the Trout Run Camp Resort.

Thunderstorm Wind in CHAUTAUQUA, NEW YORK
From 09-JUN-21 16:25:00 to 09-JUN-21 16:25:00 (EST-5)
Location: STILLWATER
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Trees were downed onto Garfield Road.

Thunderstorm Wind in CHAUTAUQUA, NEW YORK
From 09-JUN-21 16:30:00 to 09-JUN-21 16:30:00 (EST-5)
Location: STILLWATER
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Trees were downed onto power lines east of Busti between Forest Avenue and South Main Street Extension.

Flash Flood in ALLEGANY, NEW YORK
From 09-JUN-21 15:15:00 to 09-JUN-21 17:15:00 (EST-5)
Location: WEST CLARKSVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

State route 305 was closed due to water flowing over the roadway.

Flash Flood in ALLEGANY, NEW YORK
From 09-JUN-21 15:20:00 to 09-JUN-21 17:20:00 (EST-5)
Location: WEST CLARKSVILLE
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A section of Hoyett Road was washed out in West Clarksville.