Summary

Another round of severe weather moved across Central Pennsylvania during the afternoon of July 27th, 2006. The local storm report showed most of the severe thunderstorms occurring in the eastern and southern portion of the county warning area. Like the July 18th event, this was another case in which thunderstorms formed in an unstable but weakly sheared environment. The morning upper air soundings taken at 1200 UTC at Pittsburgh, PA and Sterling, VA showed high CAPE values (2144 and 2980 J/Kg, respectively) but weak unidirectional vertical wind shear. This indicated that the storms would tend to be non-rotating and only produce hail and strong winds.

As the storms developed in the mid afternoon they began to get more organized. At 19:38 UTC (3:38 pm) a cluster of thunderstorms moved into central Snyder county and by 19:54 UTC (3:54 pm) these storms were producing wind damage around Sellinsgrove and Sunbury in eastern Snyder and western Northumberland counties. Around 4:05 pm and 4:15 pm emergency managers reported trees down around Sunbury where the radar showed a very strong thunderstorm moving through the area at 20:07 UTC (4:07 pm).

By 4:30 pm the severe weather action shifted south across Adams and York counties. Trees and wires were reported to be blown down in East Berlin on the Adams and York county line where radar showed a strong storm at 20:29 UTC (4:29 pm). This storm traveled northeast and also produced wind damage around Lewisbury in northeast York county at 4:55 pm. Several trees were blown down in Swatara Township as it moved across southern Dauphin county around 5:10 pm (21:10 UTC).

Meanwhile the severe action was just getting started across Lancaster county. Around 20:30 UTC (4:30 pm) an isolated thunderstorm developed across north central Lancaster county and moved east toward Denver at 20:47 UTC (4:47 pm). Emergency managers reported wind damage and trees down at 5:10 pm in the town of Denver with this storm. At the same time in western Lancaster county a group of thunderstorms was moving east out of southern Dauphin county and producing nickel size hail 1 mile north of Elizabethtown. By 5:35 (21:35 UTC) pm a little farther to the north thunderstorms were producing severe winds in Lebanon where the roof of a building was damaged.

By 6:00 pm the severe weather had moved into eastern Lancaster county. A loop of the visible satellite imagery and lightning strikes showed the storms had increased in intensity. Radar at 22:12 UTC (6:12 pm) showed the storms had organized into a line and the Vertically Integrated Liquid product showed very high values indicating the potential for large hail. A few minutes later at 6:15 pm penny size hail was reported at Gap in far eastern Lancaster county.

PRELIMINARY LOCAL STORM REPORT...CORRECTED
 NATIONAL WEATHER SERVICE STATE COLLEGE PA
 1052 PM EDT THU JUL 27 2006
 
 ..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
 ..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
             ..REMARKS..
 
 0359 PM     TSTM WND DMG     SSE SELINSGROVE         40.80N 76.87W
 07/27/2006                   SNYDER             PA   EMERGENCY MNGR 
 
             TREES DOWN IN THE ISLE OF QUE.
 
 0405 PM     TSTM WND DMG     4 S SUNBURY             40.80N 76.79W
 07/27/2006                   NORTHUMBERLAND     PA   EMERGENCY MNGR 
 
             ONE TREE DOWN IN LOWER AUGUSTA TOWNSHIP.
 
 0415 PM     TSTM WND DMG     4 NE SUNBURY            40.90N 76.73W
 07/27/2006                   NORTHUMBERLAND     PA   EMERGENCY MNGR 
 
             TREES DOWN ALONG ROUTE 145 IN UPPER AUGUSTA TOWNSHIP.
 
 0430 PM     TSTM WND DMG     EAST BERLIN             39.94N 76.98W
 07/27/2006                   ADAMS              PA   EMERGENCY MNGR 
 
             TREES AND POWER LINES DOWN.
 
 0455 PM     TSTM WND DMG     3 E LEWISBERRY          40.14N 76.80W
 07/27/2006                   YORK               PA   EMERGENCY MNGR 
 
             ONE TREE DOWN IN NEWBERRY TOWNSHIP.
 
 0510 PM     TSTM WND DMG     MIDDLETOWN              40.20N 76.73W
 07/27/2006                   DAUPHIN            PA   EMERGENCY MNGR 
 
             SEVERAL TREES DOWN IN LOWER SWATARA TOWNSHIP.
 
 0510 PM     TSTM WND DMG     DENVER                  40.23N 76.14W
 07/27/2006                   LANCASTER          PA   EMERGENCY MNGR 
 
             TREES DOWN IN DENVER AND ADAMSTOWN.
 
 0515 PM     HAIL             1 N ELIZABETHTOWN       40.17N 76.60W
 07/27/2006  M0.88 INCH       LANCASTER          PA   TRAINED SPOTTER
 
             NICKEL SIZE HAIL AND WINDS ESTIMATED AT 60 MPH.
 
 0535 PM     TSTM WND DMG     LEBANON                 40.34N 76.42W
 07/27/2006                   LEBANON            PA   EMERGENCY MNGR 
 
             ROOF OF A BUILDING DAMAGED IN LEBANON.
 
 0615 PM     HAIL             GAP                     39.99N 76.02W
 07/27/2006  E0.75 INCH       LANCASTER          PA   TRAINED SPOTTER
 
             PENNY SIZE HAIL REPORTED IN GAP.
 
 1005 PM     TSTM WND DMG     YORK SPRINGS            40.01N 77.12W
 07/27/2006                   ADAMS              PA   EMERGENCY MNGR 
 
             TREES AND WIRES DOWN.

Images

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KLWX 1200 UTC upper air sounding showing high CAPE (2980 J/kg) and weak, unidirectional shear.

Thunderstorms producing wind damage around Sellinsgrove and Sunbury in eastern Snyder and western Northumberland counties at 19:54 UTC (3:54 pm).

Around 4:05 pm and 4:15 pm emergency managers reported trees down around Sunbury where the radar showed strong storms at 20:07 UTC (4:07 pm).

Trees and wires were reported to be blown down in East Berlin on the Adams and York county line at 20:29 UTC (4:29 pm).

Isolated storm over central Lancaster county and moving east toward Denver at 20:47 UTC (4:47 pm).

By 5:35 (21:35 UTC) pm thunderstorms were producing severe winds in Lebanon where the roof of a building was damaged.

Vertically Integrated Liquid product at 22:12 UTC (6:12 pm) showed very high values indicating the potential for large hail. A few minutes later at 6:15 pm penny size hail was reported at Gap in far eastern Lancaster county.