Sweaty Philadelphians are bracing Tuesday for what could be the city's first 100-degree day in more than a decade. But the region already recorded a much stranger weather milestone this week: record-breaking snowfall in July.
The National Weather Service station at Mount Holly observed trace amounts of snow at Philadelphia International Airport on Sunday afternoon. The snow, in this case, was not fluffy white flakes but small hail produced by the thunderstorms that passed over the airport. Since hail is frozen precipitation, it's considered a "trace" of snowfall, a classification for snow that melts upon hitting the ground and never accumulates over 0.1 inches.
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"If it's cold enough high up in the atmosphere, if there's a strong enough updraft, ice droplets as well as rain droplets can essentially just tumble," Mike Lee, a meteorologist for NWS Mount Holly, explained. "... They'll actually accumulate and grow into essentially a hailstone. And then once it weighs enough and the updraft becomes a little weaker, it'll then fall back down to earth. And that's how we get hail.
"It can be pretty common with severe thunderstorms."
The recent hail marked the first time the weather station recorded hail or any type of frozen precipitation in Philadelphia on July 14. NWS Mount Holly has been operating since 1870.
Traces of snow in the summer are unusual, but not impossible. An NWS list of other instances of trace snowfall due to to hail from thunderstorms includes dates in August 2011, July 2008 and June 1911. That also means, despite the sweltering temperatures, Philadelphia could see more "snow" before the summer ends.
"It's very possible," Lee said. "We could get it with any severe thunderstorm."
There's a chance of storms hitting the city again Tuesday through Thursday night, though it's unclear if they'll be severe enough to cause more hail. Here's the current NWS forecast, as of Tuesday afternoon:
TUESDAY: Mostly sunny and hot, high temperature near 100. Chance of showers and thunderstorms, mainly before 1 a.m.
WEDNESDAY: Showers and thunderstorms likely, mainly after 2 p.m. Mostly sunny, high near 96. Showers and thunderstorms also likely before 2 a.m, then showers likely and possibly a thunderstorm after 2 a.m.
THURSDAY: Chance of showers and thunderstorms after 2 p.m. Partly sunny, high near 86. Then a chance of showers and thunderstorms before 8 p.m. Partly cloudy, with a low around 69.
FRIDAY: Sunny high near 87. Partly cloudy in the evening, low around 68.
SATURDAY: Partly sunny, high temperature near 86. Partly cloudy in the evening, with a low around 70.
SUNDAY: Mostly sunny, high near 91. Partly cloudy in the evening, low around 71.
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