Summary

For the second straight day, York County, PA, bore the brunt of the Thunderstorms that formed over Central PA. The afternoon and evening brought many thunderstorms to the state, but the repeated thunderstorms over York County produced a widespread flooding event that affected most of the southern two-thirds of the county. The rains were less concentrated than the day before, but the already-wet ground and torrential downpours produced many more flooding reports than Thursday (the 1st). Traffic on the southbound side of Interstate 83 to the south of the City of York (near the Glen Rock Exit) was slowed or stopped due to a foot or more of water on the roadway surface. In addition to the flooding, a rotating thunderstorm cell produced at least two incidents of wind damage south of the City of York.

Preliminary Damage Reports in Text format

Images

Infrared Satellite Picture from 2203z (603pm EDT) with multiple storms over York County.

KCCX WSR-88D One Hour Precipitation Estimate from 2105z through 2205z for York County. Note the yellow colors inside the purples, indicating possibly over two inches of rain in just one hour! These estimates were deemed very accurate, as very little hail was reported from these storms, and the precipitation algorithm setting that was incorrect the day before (the 1st) had been corrected by NWS CTP Staff. Again, this area received torrential rains in one hour (then additional rain later), with a well-corroborated rain gage report from a storm spotter in the area of 2.5 inches of rain in just an hour and a half.

KCCX WSR-88D Storm Relative Motion from 2203z. Note the red and green colors right next to each other (a velocity couplet) over South-Central York County indicating a mesocyclone (mid-level cyclonic rotation) in the thunderstorm cell. This cell is the one that produced the wind damage, and it also contributed to the flooding. The mesocyclone was an indication of the very strong updraft in the storm.
People often ask us - "What is the advantage of a Doppler Radar?" Well - this is it! We (as radar operators) can see the storm-scale rotation, and make inferences about the strength and severity of the individual storm cells. Not every storm has the potential to make wind damage and hail, and the doppler radar gives us the ability to infer more about the storm from it's structure than we could with only reflectivity.

KCCX WSR-88D Reflectivity from 2203z. This is the same time and view of the SRM picture immediately above. Note the strong reflectivities, and the sharp gradient on the southeastern side of the cell. This is sometimes a sign of rotation and a mesocyclone, and corresponds very well with the SRM pic above.