Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* A hot, humid and stormy start to september *

2:00 p.m. Tuesday, September 1, 2026:

Meteorological summer, and August, ended on a warm and muggy note with high temperatures in the low-to-mid 80s across the Lower Susquehanna Valley Monday afternoon, and meteorological fall is kicking off on an ever hotter and stickier note this afternoon. Behind Monday night's warm frontal passage, west-southwesterly winds have ushered unseasonably hot and humid air into northern MD and southeastern PA, and temperatures should peak in the upper 80s to low 90s this afternoon under partly-to-mostly sunny skies. When combined with dewpoints in the low-to-mid 70s, max heat indices will be near 100°F in most spots (see below). If you have prolonged, outdoor plans, drink plenty of non-alcoholic beverages and take frequent breaks in an air-conditioned room or building to stay hydrated and cool. The Commonwealth will be on the northeastern periphery of an upper-level Jet Stream ridge, or "heat dome," centered over the Southeast and Tennessee River Valley through the end of the week. Meteorologists often refer to this zone as the "ring of fire" due to frequent bouts of showers and thunderstorms within this corridor of relatively fast, northwesterly flow. This case will be no exception, and severe weather will even be a concern on Wednesday and Thursday. The first in a series of disturbances is currently moving through northeastern PA and southern New England, but I don't expect much in the way of shower/thunderstorm activity southwest of the Lehigh Valley through tonight. A stray shower or storm may impact a few spots east of the Susquehanna River, but any severe weather concerns will likely be farther north/east (see below). 

A backdoor cold front, or one that moves from northeast-to-southwest, will move through the eastern half of PA tonight and serve as the focal point for more thunderstorms on Wednesday. How far south/west it gets before stalling will determine where the corridor of severe weather occurs in PA. The zone may be no more than 50-100 miles wide, so trying to pinpoint it even 24 hours in advance is quite challenging. Odds favor the western half of the Lower Susquehanna Valley to the I-99 corridor over areas farther east, but only time will tell. Due to light, easterly flow and enhanced cloud cover behind the front, high temperatures on Wednesday will be around 5-15°F lower than this afternoon and range from the mid 70s near Philadelphia to mid-to-upper 80s in Franklin County. The backdoor cold front will then lift back northeastward as a warm front from Wednesday night into Thursday morning. Thus, south-central PA will be in the warm sector again on Thursday with high temperatures, dewpoints and heat indices similar to this afternoon under partly sunny skies. However, a traditional cold front will then sag southward through the Commonwealth later Thursday into Friday morning and trigger yet another round of locally strong-to-severe thunderstorms (see below). At this point, Thursday's round of storms looks like a late-day or evening affair between 4-11 PM, but the exact timing may change by a couple of hours. Regardless, the most intense storms both Wednesday and Thursday will be capable of producing frequent lightning, torrential downpours, localized flash flooding of low-lying, urban- and poor-drainage areas, small hail and damaging wind gusts up to 65 mph. Motorists may face delays and encounter standing water and debris on some roadways each afternoon/evening, and isolated power outages are also a "good bet" in the hardest-hit spots. Seek shelter in an interior room or basement if a severe thunderstorm warning is issued for your location!

Behind the front, winds will finally turn northwesterly on Friday and usher cooler, drier and less humid air into the mid-Atlantic States just in time for Labor Day Weekend. The frontal boundary may still be draped somewhere over the Delmarva Region on Friday and in close enough proximity to bring some additional showers to southern PA and northern MD, but any thunderstorm activity should remain south of Interstate 70. Dewpoints may still be in the upper 60s to perhaps 70°F on Friday, but high temperatures should only reach the low-to-mid 80s on account of the clouds, scattered showers and northwesterly flow. The front will finally push farther south Friday night, and a high pressure system of Canadian origin is then expected to settle into the Northeast over the holiday weekend. The large-scale subsidence, or sinking motion, beneath the high will likely promote mainly clear skies, low humidity and comfortable conditions both locally and at the Jersey, Delaware and Maryland beaches this weekend. Dewpoints should tumble into the upper 50s or low 60s by Saturday morning and then remain there through Labor Day itself. Overnight lows on Saturday and Sunday nights will be similar to the dewpoints, and afternoon highs should be in the low 80s on Saturday, upper 70s Sunday and low 80s again on Monday. Light, east-to-northeasterly flow along the coast may keep high temperature slightly lower at the beaches on Sunday and Monday, but the weather should still be great for beach vacations or local, outdoor gatherings with family and friends. I expect no interruptions from showers, thunderstorms or dangerously hot conditions, and that's an ideal, "unofficial" end to summer in my book! Check back Friday for a brief update. -- Elliott