A cold front approached Pennsylvania from the northwest on Friday, the 7th of October, while a plume of deep tropical moisture flowed up into the mid-atlantic from the east. This tropical moisture and the circulation that accompanied it were the remnants of once-Tropical Storm Tammy.
Infrared Sat Pic from the 7th, with cold front overlaid. (Former) TS Tammy circulation over GA/SC.
Heavy rain was the result. Amounts approached or exceeded 6 inches in places to the east of the Susquehanna River, with the heaviest totals near Lancaster, PA - as a widespread 8 to 12 inches of rain fell there. The rest of Central PA had 2-5 inches of rain. (See pictures below).
Generally, only Minor Flooding of smaller creeks and streams happened, as the area had been very dry for the entire summer.
The dry antecedent conditions helped to keep the flooding from becoming worse in most areas.
However, Major Flooding occurred in Lancaster County, where many roads were closed due to high water for as much as an entire day, and many homes and businesses had water damage.