Low pressure tracked northeastward across Michigan and eastern Canada, pushing a warm front across western Pennsylvania in the morning, with some showers and thunderstorms ahead of it.  Breaks in the clouds behind this morning activity allowed instability to build once again during the afternoon.  The environment behind the warm front was favorable for severe weather with strong wind shear and deep moisture.  Several discrete storms were able to form, with rotation and bounded weak echo regions noted in a few storms.  However, the only reports of damage were received from Jefferson County.  Several reports of trees and wires being blown down were received, and a confirmed EF-1 tornado occurred near Brockway before crossing into Elk County.

Flood in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:30:00 to 21-AUG-18 17:45:00 (EST-5)
Location: REYNOLDSVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

County 911 officials reported that Route 950 was flooded near Vo-Tech Road.

Flood in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:27:00 to 21-AUG-18 17:45:00 (EST-5)
Location: RED MILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported road flooding at Airport Road and Stevenson Hill Road.

Flood in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:30:00 to 21-AUG-18 17:45:00 (EST-5)
Location: CRENSHAW
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported that Route 219 was flooded near Brockway.

Flash Flood in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 18:35:00 to 21-AUG-18 21:38:00 (EST-5)
Location: BROCKWAY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported that water was up to the first floor of a home, and the residents were evacuated.

Flood in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 14:30:00 to 21-AUG-18 17:45:00 (EST-5)
Location: PINE CREEK
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported roadway flooding at Richards Street and Melba Lane.

Flood in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:00:00 to 21-AUG-18 17:45:00 (EST-5)
Location: EMERICKVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported roadway flooding along Route 322 between Reynoldsville and Brookville.

Tornado in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:08:00 to 21-AUG-18 15:10:00 (EST-5)
Location: CRENSHAW
Tornado F-scale: EF1
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A ground survey was conducted and found the starting point at
Fermantown Road where three hardwood trees were knocked down.
The storm headed northeast to Coder Road where several homes had
trees fall on them. One house had a large tree limb pierce
through the ceiling. A large tractor was flipped over. This area had
the worst property damage of the entire path.  The tornado then crossed
into Elk County.

Thunderstorm Wind in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:10:00 to 21-AUG-18 15:10:00 (EST-5)
Location: LANES MILLS
Magnitude: 50.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported that trees and power lines were blown down along Route 219 at Harveys Run Road.

Thunderstorm Wind in JEFFERSON, PENNSYLVANIA
From 21-AUG-18 15:13:00 to 21-AUG-18 15:13:00 (EST-5)
Location: LANES MILLS
Magnitude: 50.00 EG
Property damage: 0.50K
Crop damage: 0.00K
Reported by: 911 Call Center

County 911 officials reported that several trees were downed along Fermantown Road near Rattlesnake Road.