Strong heating of a very moist low level air mass aided severe thunderstorm development during the afternoon and evening over the south central mountains and lower Susquehanna valley. Despite weak upper level support and vertical wind shear, several storms produced damaging winds and hail up to one inch in diameter. In addition, this environment proved to be favorable for slow-moving/training storms which resulted in localized flash flooding in Lancaster County.

Flash Flood in LANCASTER, PENNSYLVANIA
From 31-MAY-10 19:00:00 to 31-MAY-10 19:09:00 (EST-5)
Location: FALMOUTH
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Torrential thunderstorm rains in excess of 3 inches in a few hours caused flash flooding in west-central Lancaster County during the evening. The areas most affected included Columbia and Marietta Boroughs and much of West Hempfield Township. Several municipal roads including State Routes 23 and 441 were closed due to flooding. A mudslide on SR 411 contributed to a three-vehicle accident. A several roads were closed in the Willow Street/Pequea Township and Lancaster areas. The Rheems Fire Department reported areas of flash flooding in Maytown. Route 30 was closed near Columbia. Several basements were flooded.
The flash flooding eventually transitioned to areal flooding later in the evening before receding around midnight.

Thunderstorm Wind in LANCASTER, PENNSYLVANIA
From 31-MAY-10 16:55:00 to 31-MAY-10 16:55:00 (EST-5)
Location: HAMILTON PARK
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds estimated near 60 mph downed several large tree limbs on the west side of Lancaster.

Thunderstorm Wind in YORK, PENNSYLVANIA
From 31-MAY-10 17:00:00 to 31-MAY-10 17:00:00 (EST-5)
Location: WRIGHTSVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm winds estimated near 60 mph downed numerous trees and wires in Wrightsville.

Hail in LANCASTER, PENNSYLVANIA
From 31-MAY-10 18:00:00 to 31-MAY-10 18:00:00 (EST-5)
Location: ELIZABETHTOWN
Magnitude: 1.25 
Crop damage: 0.00K
Reported by: Broadcast Media

Hail in YORK, PENNSYLVANIA
From 31-MAY-10 18:15:00 to 31-MAY-10 18:15:00 (EST-5)
Location: ROLER
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: Broadcast Media

Heavy Rain in LANCASTER, PENNSYLVANIA
From 31-MAY-10 18:20:00 to 31-MAY-10 18:20:00 (EST-5)
Location: HAMILTON PARK
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter reported over 3 inches of rain in 1-2 hours.

Hail in LANCASTER, PENNSYLVANIA
From 31-MAY-10 15:50:00 to 31-MAY-10 15:50:00 (EST-5)
Location: WILLOW STREET
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: Trained Spotter

Quarter size hail reported at the intersection of Routes 222 and 741 just north of Willow Street.

Thunderstorm Wind in CLEARFIELD, PENNSYLVANIA
From 31-MAY-10 16:30:00 to 31-MAY-10 16:30:00 (EST-5)
Location: CURWENSVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: County Official

Thunderstorm winds estimated near 60 mph downed trees and wires along Route 453 near Curwensville.

Hail in LANCASTER, PENNSYLVANIA
From 31-MAY-10 16:45:00 to 31-MAY-10 16:45:00 (EST-5)
Location: MILLERSVILLE
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: Trained Spotter

Nickel to quarter size hail reported at Millersville University.

Hail in LANCASTER, PENNSYLVANIA
From 31-MAY-10 16:50:00 to 31-MAY-10 16:50:00 (EST-5)
Location: HAMILTON PARK
Magnitude: 0.75 
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in LANCASTER, PENNSYLVANIA
From 31-MAY-10 16:55:00 to 31-MAY-10 16:55:00 (EST-5)
Location: HAMILTON PARK
Magnitude: 0.88 
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in SOMERSET, PENNSYLVANIA
From 31-MAY-10 13:40:00 to 31-MAY-10 13:40:00 (EST-5)
Location: ADDISON
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 60 mph downed trees in Addison.

Thunderstorm Wind in WARREN, PENNSYLVANIA
From 31-MAY-10 14:35:00 to 31-MAY-10 14:35:00 (EST-5)
Location: TIDIOUTE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: County Official

Thunderstorm winds estimated near 60 mph downed numerous trees in Deerfield Township just north of Tidioute.

Thunderstorm Wind in WARREN, PENNSYLVANIA
From 31-MAY-10 14:30:00 to 31-MAY-10 14:30:00 (EST-5)
Location: SUGAR GROVE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: County Official

Thunderstorm winds estimated near 60 mph downed numerous trees in the Sugar Grove area.

Thunderstorm Wind in CAMBRIA, PENNSYLVANIA
From 31-MAY-10 14:55:00 to 31-MAY-10 14:55:00 (EST-5)
Location: SUMMERHILL
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: County Official

Thunderstorm winds estimated near 60 mph downed numerous trees in Summerhill.

Hail in CAMBRIA, PENNSYLVANIA
From 31-MAY-10 15:23:00 to 31-MAY-10 15:23:00 (EST-5)
Location: BUCKHORN
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: County Official

Dime to quarter size hail covering the ground in the village of Buckhorn on Route 36 near the Cambria/Blair line.

Flash Flood in LANCASTER, PENNSYLVANIA
From 31-MAY-10 17:30:00 to 31-MAY-10 18:59:00 (EST-5)
Location: FALMOUTH
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Torrential thunderstorm rains in excess of 3 inches in a few hours caused flash flooding in west-central Lancaster County during the evening. The areas most affected included Columbia and Marietta Boroughs and much of West Hempfield Township. Several municipal roads including State Routes 23 and 441 were closed due to flooding. A mudslide on SR 411 contributed to a three-vehicle accident. A several roads were closed in the Willow Street/Pequea Township and Lancaster areas. The Rheems Fire Department reported areas of flash flooding in Maytown. Route 30 was closed near Columbia. Several basements were flooded.
The flash flooding eventually transitioned to areal flooding later in the evening before receding around midnight.

Flood in LANCASTER, PENNSYLVANIA
From 31-MAY-10 19:09:00 to 31-MAY-10 23:00:00 (EST-5)
Location: FALMOUTH
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Torrential thunderstorm rains in excess of 3 inches in a few hours caused flash flooding in west-central Lancaster County during the evening. The areas most affected included Columbia and Marietta Boroughs and much of West Hempfield Township. The flash flooding transitioned to areal flooding later that night before receding around midnight.