As many as eight to 10 inches of rain have been recorded across parts of Pennsylvania and into northern Maryland over the past week. Places that saw a desertlike start to the month are now surpassing July rainfall records and even all-time monthly tallies.
With the worst of the rain focused on the central and east-central parts of Pennsylvania, State College and Williamsport are among locations that have set July rainfall records. So has Baltimore to the south. There are and will be others.
When you get this much rain in such a short amount of time, the ground becomes saturated, and any additional rain readily runs off. Then we see creeks and rivers rise.
The NWS Middle Atlantic River Forecast Center (MARFC) is monitoring flooding or near-flooding rivers and tributaries from the New York/Pennsylvania border to Southeastern Virginia. In addition to much of east-central Pennsylvania being under a generalized flood warning through Wednesday evening, minor to major river flooding is ongoing at about two dozen gauges across the state and into parts of neighboring states.
The rising Susquehanna River in Harrisburg is forecast to crest two feet above flood stage Friday morning.
Of most short-term urgency, MARFC is warning of major flooding on Swatara Creek near Hershey, Pa.
A “high risk” of excessive rainfall that could cause flooding is ongoing Wednesday for portions of Pennsylvania. This is the most severe level, and it is an indication of major flooding either ongoing, imminent or both. A “moderate risk” extends into northern Maryland, and much of the D.C. region is at “slight risk.” These areas are likely to also experience more flooding but, perhaps, on a more localized scale.
Early Wednesday afternoon, it wrote, “Increasing coverage of thunderstorms with 1-2 in/hr rain rates is expected across portions of the northern Mid-Atlantic/central Appalachians into upstate NY through the afternoon with localized maxima of 2-4 inches through [mid-evening].”
NWS State College, Pa., handles much of the area dealing with the worst of the flooding.
Thinking of the rain still to come, Wednesday morning, it wrote that some models show “amounts of 3+ inches later today over the eastern half of the forecast area.” Further, “The heavy rain of recent days have left most of the region very susceptible to flooding, with 1 hour flash flood values of only around a half inch.”
At this point, any rain is too much rain. Even if no more falls, and it will, many rivers and creeks would continue to rise through at least late this week. Additional flooding problems remain likely even once the rain from this series of storms ends.