Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* another round of severe storms and flooding concerns today *

1:30 p.m. Tuesday, July 28, 2026:

The last week of July kicked off on a partly-to-mostly sunny and seasonably warm note across the Lower Susquehanna Valley with high temperatures in the mid-to-upper 80s Monday afternoon. Unfortunately, the tranquil conditions will be replaced by another round of severe thunderstorms and flash flooding concerns this afternoon and evening. The Storm Prediction Center (SPC) has placed areas south/east of I-78/81 in a "slight risk" for severe weather, and the Weather Prediction Center (WPC) has outlined a "slight risk" for flash flooding across northern MD/south-central PA and "moderate risk" in southeastern PA. A vigorous, upper-level disturbance and its associated storm system will move from the eastern Great Lakes region into southern New England over the next 24-36 hours and trigger showers and heavy, drenching thunderstorms along a trailing cold front (see below). Following this morning's round of activity, a second round will sweep through the region between 2-8 PM.

Although sunshine between the rounds has been limited, the upper-level disturbance moving through the Commonwealth is quite intense and impressive by late-July standards. In addition, the atmosphere will be sufficiently moist and unstable for rapid thunderstorm development and growth with dewpoints in the low 70s and temperatures in the low 80s. Thus, the most intense storms will produce blinding downpours, frequent lightning, small hail, localized flash flooding of urban-, low-lying and poor-drainage areas, and damaging wind gusts up to 60 mph. Any wind damage in the form of downed trees or powerlines should be relatively sparse. Instead, the flash flooding threat will be the biggest and most widespread concern. Rainfall rates could briefly reach 3" per hour in the worst storms, and areas hit repeatedly by torrential downpours could receive as much as 3-5" of rain. As such, a Flood Watch is in effect until 2 AM Thursday for northern MD and the Lower Susquehanna Valley and until 2 PM Thursday in southeastern PA (see below). 3-hour flash flood guidance values range from 3-5" across the region, so creek and river flooding won't be a concern. However, some smaller streams could overflow their banks, mainly across the eastern third of PA. Be alert for debris and standing water on some roadways during the PM commute, and seek shelter in an interior room or basement if a severe thunderstorm warning is issued. Never drive through floodwaters, either! A mere 12-18" of water can float many vehicles, and 2 feet of rushing water can sweep most of them away. 

Storms should push south/east of I-95 between 7-9 PM, and no more than an additional shower or two is expected overnight. The aforementioned cold front will also sweep through the region late this evening, and winds will turn northwesterly after midnight. The northwesterly flow will then persist through Thursday night, cause skies to at least partially clear late tonight, and usher slightly cooler and drier air into the Lower Susquehanna Valley. It's strange to see during the "Dog Days" of summer, but a closed-off, upper-level low will develop over NY State tonight and then meander through southern New England until Thursday night. Fortunately, most of PA and the Delmarva Region will be in the "subsidence zone" on the system's southwestern flank. In this region, large-scale, sinking motion will thwart additional thunderstorm development and allow for no more than an isolated shower or two to erupt each afternoon/evening (see below). Morning sunshine will be of the "self-destruct" variety with a pocket of cooler air aloft overhead, but high temperatures should still only be around 5°F below average and range from near 80°F along I-81 to the mid 80s in the I-95 corridor. A refreshing, 12-25 mph breeze will accompany the comfortable conditions and knock dewpoints back down into the mid 60s on Wednesday and low-to-mid 60s Thursday/Friday. 

Both the surface- and upper-level lows will finally exit into the western Atlantic by Thursday afternoon and move much farther out to sea by the end of the week. In their wake, an area of high pressure will settle into the mid-Atlantic States and central Appalachians and promote dry and seasonably warm conditions both Friday and Saturday. Skies should be mainly clear from Thursday night through Friday night and then partly sunny on Saturday with high temperatures in the mid 80s each afternoon and overnight lows in the low-to-mid 60s. The next, slow-moving storm system may then move close enough to renew the threat for showers and thunderstorms during the second half of the weekend and/or early next week. Those details will remain nebulous for a few more days, so check back Friday for an update! Regardless, the first weekend of August will be quite typical of summer and "nothing to write home about" weatherwise, and the first half will likely be better than the second for outdoor activities. -- Elliott