Flash Flooding event of 12 Aug 2010
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Flash Flooding event of 12 Aug 2010
High moisture values were tapped by a weak Mesoscale Convective Vortex (MCV) that rolled NW to SE through the state during the middle of the day on August 12th. The vortex touched off numerous showers and thunderstorms with torrential rain falling over the lower Susquehanna valley during the afternoon. Capital City Airport (KCXY) recorded over 3 inches of rain in just one hour, while Harrisburg International Airport (KMDT) received less than three-quarters of an inch of rain during the same time. This is a perfect example of how your neighbor can have much different weather than you -- CXY and MDT are only 3 miles apart.

The torrential rain caused flash flooding in many spots -- especially over Harrisburg City, northern York County and southern Adams County. Much of the area received rainfall during the early morning hours which set the stage for the rainfall in the afternoon to quickly run off into the local low spots and small creeks and streams. The urbanized areas of the Harrisburg metro area bore the brunt of the flooding reports, mainly due to the intensity of the rain over the area, but also because the concrete and other impervious surfaces do not allow water to soak into the ground. That rain rapidly runs downhill and collects at low spots and bottle necks/constrictions like underpasses and culverts.

A few water rescues occurred during the late afternoon and evening and a few people were evacuated from their residences in the southern part of the City of Harrisburg. See the preliminary storm reports and some associated images below:


PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE STATE COLLEGE PA
600 PM EDT THU AUG 12 2010

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..

0300 PM HEAVY RAIN 2 NE HARRISBURG 40.30N 76.86W
08/12/2010 M1.00 INCH DAUPHIN PA TRAINED SPOTTER

ONE INCH IN 45 MINUTES AT PAXTONIA. MINOR FLOODING NEAR
FISHING CREEK.

0305 PM HEAVY RAIN 1 E HARRISBURG 40.28N 76.87W
08/12/2010 E2.00 INCH DAUPHIN PA TRAINED SPOTTER

TWO INCHES PER HOUR AT PROGRESS.

0335 PM HEAVY RAIN SHIREMANSTOWN 40.22N 76.96W
08/12/2010 M0.50 INCH CUMBERLAND PA TRAINED SPOTTER

0.50 IN 15 MINUTES. STREET FLOODING IN LOWER ALLEN
TOWNSHIP. TWO INCHES TOTAL SO FAR TODAY.

0351 PM FLASH FLOOD MOUNT HOLLY SPRINGS 40.11N 77.18W
08/12/2010 CUMBERLAND PA COUNTY OFFICIAL

911 CENTER REPORTED UNDERPASS FLOODED. ROADS PONDED.

0400 PM HEAVY RAIN YORK SPRINGS 40.01N 77.12W
08/12/2010 M0.87 INCH ADAMS PA NWS EMPLOYEE

0.87 IN ONE HOUR WITH THUNDERSTORM BETWEEN 3 PM AND 4 PM.


0400 PM HEAVY RAIN 4 S NEW CUMBERLAND 40.17N 76.88W
08/12/2010 U0.00 INCH YORK PA COUNTY OFFICIAL

911 CENTER REPORTED WATER RESCUE AND SEVERAL HOUSES
STRUCK BY LIGHTNING.

0400 PM HEAVY RAIN 2 SE NEW CUMBERLAND 40.21N 76.85W
08/12/2010 M3.01 INCH YORK PA ASOS

3.01 INCHES IN ONE HOUR AT CAPITAL CITY AIRPORT.

0400 PM FLASH FLOOD GETTYSBURG 39.83N 77.23W
08/12/2010 ADAMS PA COUNTY OFFICIAL

911 CENTER REPORTED SEVERAL VEHICLES STALLED IN FLOODED
ROADWAYS.

0400 PM FLASH FLOOD 7 NW GOLDSBORO 40.23N 76.84W
08/12/2010 YORK PA COUNTY OFFICIAL

911 CENTER REPORTED 2 PERSONS RESCUED FROM VEHICLE
STRANDED IN FLOODED ROADWAY AT LEWISBERRY AND FAIRVIEW
ROADS IN FAIRVIEW TOWNSHIP.

0409 PM HEAVY RAIN MECHANICSBURG 40.21N 77.01W
08/12/2010 M1.10 INCH CUMBERLAND PA TRAINED SPOTTER

1.10 IN 35 MINUTES. URBAN FLOODING. SOME ROADS IMPASSIBLE
WITH 2 FEET OF WATER.

0430 PM FLASH FLOOD HARRISBURG 40.28N 76.88W
08/12/2010 DAUPHIN PA COUNTY OFFICIAL

911 CENTER REPORTED MULTIPLE STREETS FLOODED THROUGHOUT
HARRISBURG AND SURROUNDING TOWNSHIPS. INTERCHANGE 283 AND
83 FLOODED. HOUSES AND VEHICLES FLOODED ESPECIALLY IN
SWATARA TOWNSHIP. FLOODING BEGAN ABOUT 3 PM AND WAS
ONGOING AT 430 PM.

0435 PM HEAVY RAIN 6 WNW GETTYSBURG 39.86N 77.34W
08/12/2010 M1.41 INCH ADAMS PA TRAINED SPOTTER

1.41 INCHES IN 35 MINUTES AT ORRTANNA.

0500 PM FLASH FLOOD HARRISBURG 40.28N 76.88W
08/12/2010 DAUPHIN PA COUNTY OFFICIAL

911 CENTER REPORTED 8 HOMES WERE EVACUATED IN THE 1200
BLOCK OF SOUTH 19TH STREET. A SHELTER WAS SET UP FOR THE
40 PERSONS THAT WERE AFFECTED.

0535 PM FLASH FLOOD 3 NE HANOVER 39.84N 76.94W
08/12/2010 YORK PA COUNTY OFFICIAL

911 CENTER REPORTED A WATER RESCUE FROM A FLOODED VEHICLE
AT THOMAN AND STENNEN ROADS IN HEIDELBERG TOWNSHIP.


&&



Visible Sat image from the morning of the 12th, note circulation from MCV over Central PA and clearing to the south
Visible Sat image from the morning of the 12th, note circulation from MCV over Central PA and clearing to the south


IR Sat image during the morning
IR Sat image during the morning


Dulles (KLWX) sounding at 12z on the 12th
Dulles (KLWX) sounding at 12z on the 12th


Precipitable Water values - note over 2 inches of water available overhead in SE PA
Precipitable Water values - note over 2 inches of water available overhead in SE PA


Early morning radar reflectivity image from KCCX - priming the ground for flooding
Early morning radar reflectivity image from KCCX


Afternoon radar reflectivity image from KCCX - heavy rain in Harrisburg and vicinity
Afternoon radar reflectivity image from KCCX - heavy rain in Harrisburg and vicinity


KCCX Storm Total Precip from the 12th. Note the maxima in the lower Susquehanna valley
KCCX Storm Total Precip from the 12th. Note the maxima in the lower Susquehanna valley


Flooding in Harrisburg, photo courtesy Dauphin County Emergency Management
Flooding in Harrisburg, photo courtesy Dauphin County Emergency Management



 
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Page Last Modified: 13 August 2010 02:54:06 UTC
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