It Felt Like Summer Until the Squall Line Came

There is a particular kind of autumn day that feels like a borrowed memory of summer, warm and humid and slightly out of place. Friday in Philadelphia was one of those days. By evening, it would be something else entirely.

The National Weather Service issued a severe thunderstorm watch for the Philadelphia region and much of the Mid-Atlantic, effective until 8 p.m. Friday. The primary threats included widespread wind gusts up to 70 mph, isolated hail, and the possibility of a couple of tornadoes . The watch covered a wide area stretching from Virginia and Washington, D.C., north through Maryland and eastern Pennsylvania, including Philadelphia, Allentown, Harrisburg, and Scranton .

The storms were expected to develop as a strong cold front swept across the region. Forecasters warned that the main wind risk could be associated with a narrow squall line crossing from west to east . In New Jersey, a separate severe thunderstorm watch was issued for all 21 counties, with the most intense storms potentially spawning an isolated tornado .

Behind the front, a dramatic change was coming. Saturday's high was forecast to reach only the mid-50s, more than 20 degrees colder than Friday's expected high near 80. Gusty northwest winds of 25 mph or more would make it feel even colder .

Sunday morning brought another alert: the potential for frost and freezing temperatures, particularly in colder northern and western suburbs, with lows falling into the 30s for the first time this season . Temperatures were expected to moderate gradually early next week, returning to the 60s and eventually the 70s .

For those with evening plans, the advice was simple: pay attention to the forecast, be prepared for rapidly changing conditions, and keep a jacket nearby. The season was shifting, and Friday evening was the moment it made itself known.

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Sources: CBS News Philadelphia, NBC10 Philadelphia, NJ.com, Yahoo News, Inquirer.com