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.
The cold front is embedded in a large area of clouds, showers and thunderstorms covering the middle of the country. It will advance past the Northeast coast by the end of the day Sunday. The frontal zone is shown on this picture from late morning Friday.
When weather systems are relatively weak, small scale variations cause forecast uncertainty because several different weather types (such as showers, sunshine, cloudiness, etc.) can coexist in the same region and change constantly. This map shows such a pattern:
Some of the thunderstorms can become severe, with damaging wind and brief cloudbursts of rain. The greatest chance for locally severe storms should be in the "S" areas highlighted on this map (based on the NWS Storm Prediction Center's guidance).
There is a slight risk for severe thunderstorms later today from north-central Tennessee up across Indiana and Ohio to Michigan and eastern Wisconsin (shown by the "S" area on the map below. Thunderstorms are not predicted for areas near the coast from Delaware to New England.
It is not going to snow any time soon, but in any type of weather the flag is a symbol of freedom. This holiday weekend we celebrate the contributions of those who were there to defend the freedoms we enjoy in these times.
Once again, the rain will miss much of central and northern New England. The region has been in a dry spell, as evidenced by its appearance on this U.S Drought Monitor map.