A fast-moving upper level impulse and attendant surface low pressure system moved across the Great Lakes Region. An unseasonably warm and relatively moist air mass /surface temperatures in the 70s to low 80s and dewpoints in the upper 50s/ resided over central Pennsylvania in advance of this system and aided in strong destabilization. The moderate instability combined with strong vertical wind shear profiles promoted organized thunderstorms with supercells and bowing line segments. Large hail and damaging winds were the main threats, however sufficient low-level wind shear was present to support isolated tornadoes. A tornado watch was issued around 1500 EDT on 27 April 2011.
The severe weather threat continued through the evening and into the overnight and early morning hours on 28 April 2011. By this time, thunderstorms had evolved into largely north-south oriented clusters or broken lines with embedded supercell structures. Above normal soil moisture from recent heavy rains combined with high stream-flows and intense short duration rainfall contributed to flash flooding. The storms finally exited the region by mid-morning on 28 April 2011.

Thunderstorm Wind in PERRY, PENNSYLVANIA
From 27-APR-11 18:15:00 to 27-APR-11 18:15:00 (EST-5)
Location: NEWPORT
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Newport.

Flash Flood in CUMBERLAND, PENNSYLVANIA
From 28-APR-11 04:56:00 to 28-APR-11 10:15:00 (EST-5)
Location: CAMP HILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Several road closures and water rescues were reported in and around New Cumberland.
Widespread flooding in Lower Allen Township. Cedar Run out of its banks flooding Old Gettysburg Road. Cars reported flooded, two homes and a business also flooded.

Flash Flood in FRANKLIN, PENNSYLVANIA
From 28-APR-11 04:00:00 to 28-APR-11 06:50:00 (EST-5)
Location: WELTYS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

East Branch of Antietam Creek out of its banks at Renfrew Park.  Water across State Line Road.

Hail in CLEARFIELD, PENNSYLVANIA
From 27-APR-11 22:12:00 to 27-APR-11 22:12:00 (EST-5)
Location: MORRISDALE
Magnitude: 0.88 
Crop damage: 0.00K
Reported by: NWS Employee

Thunderstorm Wind in LEBANON, PENNSYLVANIA
From 28-APR-11 03:55:00 to 28-APR-11 03:55:00 (EST-5)
Location: MYERSTOWN
Magnitude: 54.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter measured a thunderstorm wind gust of 62 mph in Myerstown. The thunderstorm winds also knocked down trees.

Thunderstorm Wind in ADAMS, PENNSYLVANIA
From 28-APR-11 04:30:00 to 28-APR-11 04:30:00 (EST-5)
Location: BIGLERVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 60 mph uprooted trees and knocked down utility wires in Biglerville.

Hail in SOMERSET, PENNSYLVANIA
From 27-APR-11 23:35:00 to 27-APR-11 23:35:00 (EST-5)
Location: BERLIN
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: Public

Hail in BLAIR, PENNSYLVANIA
From 28-APR-11 00:35:00 to 28-APR-11 00:35:00 (EST-5)
Location: (AOO)BLAIR CO ARPT A
Magnitude: 1.25 
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in ADAMS, PENNSYLVANIA
From 28-APR-11 04:42:00 to 28-APR-11 04:42:00 (EST-5)
Location: BERMUDIAN
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down several trees in Lake Meade.

Thunderstorm Wind in YORK, PENNSYLVANIA
From 28-APR-11 04:47:00 to 28-APR-11 04:47:00 (EST-5)
Location: ROSSVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 60 mph knocked down numerous trees near Wellsville.

Thunderstorm Wind in CENTRE, PENNSYLVANIA
From 28-APR-11 01:30:00 to 28-APR-11 01:30:00 (EST-5)
Location: BOALSBURG
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Boalsburg.

Thunderstorm Wind in LEBANON, PENNSYLVANIA
From 28-APR-11 05:35:00 to 28-APR-11 05:35:00 (EST-5)
Location: EAST HANOVER
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 60 mph knocked down trees near Harper Tavern.

Thunderstorm Wind in SNYDER, PENNSYLVANIA
From 28-APR-11 02:35:00 to 28-APR-11 02:35:00 (EST-5)
Location: MIDDLEBURG
Magnitude: 61.00 EG
Property damage: 7.50K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated between 60 and 70 mph knocked down trees and caused minor structural damage in Middleburg. The structural damage was generally limited to only one or two concentrated areas.

Thunderstorm Wind in CENTRE, PENNSYLVANIA
From 28-APR-11 01:40:00 to 28-APR-11 01:40:00 (EST-5)
Location: CENTRE HALL
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Centre Hall.

Thunderstorm Wind in NORTHUMBERLAND, PENNSYLVANIA
From 28-APR-11 02:55:00 to 28-APR-11 02:55:00 (EST-5)
Location: DALMATIA
Magnitude: 61.00 EG
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Department of Highways

Thunderstorm winds estimated near 70 mph knocked down several trees and damaged a trailer in Dalmatia. Two people were extracted from the trailer but sustained no injuries.

Thunderstorm Wind in MIFFLIN, PENNSYLVANIA
From 28-APR-11 01:45:00 to 28-APR-11 01:45:00 (EST-5)
Location: NEWTON HAMILTON
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Lucy Furnace.

Thunderstorm Wind in MIFFLIN, PENNSYLVANIA
From 28-APR-11 02:07:00 to 28-APR-11 02:07:00 (EST-5)
Location: LEWISTOWN
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees along SR 22.

Thunderstorm Wind in JUNIATA, PENNSYLVANIA
From 28-APR-11 02:20:00 to 28-APR-11 02:20:00 (EST-5)
Location: MC ALISTERVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm winds estimated near 60 mph knocked down trees in McAlisterville.

Thunderstorm Wind in LANCASTER, PENNSYLVANIA
From 28-APR-11 08:46:00 to 28-APR-11 08:46:00 (EST-5)
Location: FARMERSVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: County Official

Thunderstorm winds estimated near 60 mph knocked down trees and numerous large limbs in West Early Township.

Hail in DAUPHIN, PENNSYLVANIA
From 28-APR-11 03:00:00 to 28-APR-11 03:00:00 (EST-5)
Location: DAUPHIN
Magnitude: 1.00 
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in LANCASTER, PENNSYLVANIA
From 28-APR-11 09:40:00 to 28-APR-11 09:40:00 (EST-5)
Location: KINZERS
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 60 mph knocked down several utility poles near U.S. Route 30 and Hoover Road in Salisbury Township.

Thunderstorm Wind in NORTHUMBERLAND, PENNSYLVANIA
From 28-APR-11 03:07:00 to 28-APR-11 03:07:00 (EST-5)
Location: REBUCK
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Rebuck.

Thunderstorm Wind in PERRY, PENNSYLVANIA
From 28-APR-11 01:58:00 to 28-APR-11 01:58:00 (EST-5)
Location: NEW GERMANTOWN
Magnitude: 65.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Thunderstorm wind damage was observed in the Tuscarora State Forest on Horse Valley Road, approximately 2 miles south of East Waterford. The wind damage was associated with the rear-flank downdraft of a strongly rotating storm that produced and EF1 tornado on the east side of East Waterford. Several large pine trees and utility wires were toppled at the intersection of Horse Valley and Kansas Valley Roads, completely blocking both roads. Damage indicators surveyed were consistent with maximum thunderstorm winds in excess of 70 mph.

Thunderstorm Wind in NORTHUMBERLAND, PENNSYLVANIA
From 28-APR-11 03:14:00 to 28-APR-11 03:14:00 (EST-5)
Location: LECK KILL
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Leck Kill.

Thunderstorm Wind in ADAMS, PENNSYLVANIA
From 28-APR-11 03:15:00 to 28-APR-11 03:15:00 (EST-5)
Location: BIGLERVILLE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Biglerville.

Flash Flood in COLUMBIA, PENNSYLVANIA
From 28-APR-11 07:15:00 to 28-APR-11 09:15:00 (EST-5)
Location: GROVANIA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Several road closures, mudslides and small stream flooding were reported.

Flash Flood in TIOGA, PENNSYLVANIA
From 28-APR-11 00:15:00 to 28-APR-11 02:00:00 (EST-5)
Location: WEST FIELD
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Small streams were reported out of their banks and road washouts reported in Westfield Township.

Thunderstorm Wind in SCHUYLKILL, PENNSYLVANIA
From 28-APR-11 03:30:00 to 28-APR-11 03:30:00 (EST-5)
Location: VALLEY VIEW
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down multiple trees in Valley View.

Flash Flood in DAUPHIN, PENNSYLVANIA
From 28-APR-11 06:00:00 to 28-APR-11 10:15:00 (EST-5)
Location: PIKETOWN
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flooding reported on Route 443.

Thunderstorm Wind in POTTER, PENNSYLVANIA
From 27-APR-11 17:15:00 to 27-APR-11 17:15:00 (EST-5)
Location: AUSTIN
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down several trees near Austin.

Thunderstorm Wind in COLUMBIA, PENNSYLVANIA
From 28-APR-11 03:35:00 to 28-APR-11 03:35:00 (EST-5)
Location: CATAWISSA
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 60 mph knocked down trees near Catawissa.

Thunderstorm Wind in CLEARFIELD, PENNSYLVANIA
From 27-APR-11 15:50:00 to 27-APR-11 15:50:00 (EST-5)
Location: DU BOIS
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees and utility wires along Quarry Avenue in DuBois.

Thunderstorm Wind in TIOGA, PENNSYLVANIA
From 27-APR-11 18:48:00 to 27-APR-11 18:48:00 (EST-5)
Location: OSCEOLA
Magnitude: 70.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 80 mph produced significant damage in Elkland Borough along SR 49 (West Main Street). Numerous trees were uprooted and large limbs fell onto nearby homes and structures, causing minor to moderate damage. A 70x35 foot barn was completely destroyed.

Thunderstorm Wind in SOMERSET, PENNSYLVANIA
From 27-APR-11 23:26:00 to 27-APR-11 23:26:00 (EST-5)
Location: GARRETT
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorm winds estimated near 60 mph knocked down trees in Garrett.

Thunderstorm Wind in UNION, PENNSYLVANIA
From 28-APR-11 02:45:00 to 28-APR-11 02:45:00 (EST-5)
Location: MIFFLINBURG
Magnitude: 65.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm winds estimated near 75 mph damaged two large barns in Mifflinburg. The first barn was completely destroyed, but appeared to be very old. The second barn was structurally-sound but lost nearly half of the roof.

Flash Flood in ADAMS, PENNSYLVANIA
From 28-APR-11 03:00:00 to 28-APR-11 10:15:00 (EST-5)
Location: ARENDTSVILLE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

Route 234 was closed due to high water.  Small stream flooding, water rescues, basements flooded and water flowing over blocking roads reported in Biglerville.