Thursday 8 a.m.
Temperatures soared to midsummer levels yesterday, including 94 in Philadelphia, 96 in New York City and 97 in Boston. It got warmer farther north because of slightly stronger winds. These helped mix initially cool, low-level air with fast-moving, hotter air a few thousand feet aloft. Stronger flow aloft goes with the season. Winds increase with height the fastest over areas with the greatest temperature contrast. In the cold season, there is a greater temperature difference between the polar regions and the tropics than in summer. In this video, we look at the shower zone and track the advance of cooler air into the Northeast. Later, we see whether this is a quick drop followed by more heat or the cooldown is more long-lasting.
Thunderstorms were widespread yesterday, especially south of the boundary between the hot, steamy air mass and the cooler air to the north. This map shows the 24-hour lightning record ending around 4 a.m. today. The cold front triggering the thunderstorms will move off the East Coast tomorrow.
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Thunderstorms will develop this afternoon from the Ohio Valley into the interior Northeast.