Thursday, June 21, 2012

Agnes At 40: The Rains Start Again

Agnes' flood waters impacted the Schuylkill and Susquehanna Basins between June 22nd and 25th, thanks to the slow-moving nature of Agnes as it pushed northeast through the Southeastern US.  As it re-emerged in the Atlantic off of the Carolina coastline, Agnes intensified somewhat and became a strong tropical storm.  However, a cool front was pushing east through the Great Lakes and the upper level trough that accompanied the front captured Agnes, pulling the tropical system back northwest into New Jersey, New York, and Pennsylvania.  Agnes stalled out.

This stall lead to prolific rains falling in Pennsylvania between the 21st and 23rd, with Philadelphia getting the lion's share of rain on the 22nd, while Northern and Central Pennsylvania picked up the brunt of the storm on the 22nd and 23rd.
Just between the 21st and 22nd, Harrisburg picked up nearly fifteen inches of rain.  Carlisle picked up nearly ten inches of rain, with Lebanon picking up 9.70" of rain between these two days, with Lebanon getting another four inches of rain on the 23rd.  Rainfall was generally highest across Central Pennsylvania in a swath from Williamsport south to York, running along and just west of I-81.

General contour of Agnes' rainfall in Pennsylvania (NWS)

The highest rainfall total from Agnes in Pennsylvania was 19", recorded at a USDA research site in a rural area of Western Schuylkill County near the village of Pitman.  Between Harrisburg and places to its north and northeast, fifteen inches of rain was common.  These rains, combined with the anywhere between eight and twelve inches of rain that fell farther north, created the flooding situation that Agnes is known for and that we'll talk about this weekend.

One of the byproducts of the weather pattern that Agnes and the upper level low produced in Pennsylvania was record cold high temperatures.  Philadelphia recorded its latest sub 60 degree high on record on June 23rd -- 58 degrees -- the coldest any high temperature had been that late in the year.  Other very cool highs for June 23rd included 54 in Scranton, 57 in Allentown, 53 in Palmerton  (near Jim Thorpe), and a brrrr-riffic 50 in Donegal in Western Pennsylvania.

Between the rain and cold, it was a miserable pattern for the latter portions of June.  The rain, compounded on top of prior rains, created an even bigger problem that ultimately cost nearly two billion dollars in damage.  Our next post will talk about Agnes' flooding.