A line of showers in Central Pennsylvania moved our way Wednesday afternoon and strengthened into thunderstorms.
The National Weather Service declared a Severe Thunderstorm Watch for the entire region through 7 p.m. Wednesday and a Severe Thunderstorm Warning for Philly and the surrounding suburbs until 6:30 p.m.
The NBC10 Weather Team issued a First Alert for the chance that some of the storms will become severe. That means downpours, locally damaging winds and hail. Most of us won’t experience those conditions, but some could.
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Thunderstorms moved through after 3 p.m. Some computer models suggest the storms could stall over part of our area this evening. That would limit the severe storm threat but increase the localized flood threat. The heavy rain caused flooding on Route 202 in Paoli, Chester County.
There are several factors that go into a severe storm threat. They involve temperatures from the ground all the way up through the atmosphere, winds through that whole layer, and moisture in that layer.
It’s like the fairy tale “Goldilocks and the Three Bears”-everything has to be just right. If the ground doesn’t heat up enough: no severe storms. If the wind is too strong or in the wrong direction at any level: no severe storms. If it’s too humid throughout the atmosphere: no severe storms. This is why most thunderstorms are not severe.
What’s the official definition of a “severe thunderstorm?" It has to either produce wind gusts of 58 mph or more, hail at least 1-inch in diameter or a tornado. Heavy rain or lightning are not specific parts of the National Weather Service definition, but we do consider those threats in declaring a First Alert Weather Day.
Even though some thunderstorms are possible Thursday, the threat of them being severe is significantly lower than today.