Extreme Heat, Humidity Continues With a Chance of Isolated Thunderstorms

The First Alert continues for dangerous heat and humidity Monday, with the possibility of strong thunderstorms in the afternoon

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A deck of Monday morning clouds associated with a passing disturbance aloft dropped showers on a few communities Monday morning. But sunshine gains a footing by midday with heat and humidity back on the docket in the afternoon. 

Our NBC10 Boston and NECN Weather Team continues a First Alert for exceptional heat and humidity – and the possibility of isolated strong thunderstorms – Monday afternoon. 

High temperatures will reach 95 to 100 degrees, securing a heat wave of three straight days of 90+ high temperatures. But the dew point temperatures are near 70 degrees, indicating that there's plenty of moisture in the air. This will push heat index values over 100 degrees from noon to 5 p.m. in much of New England. 

Many ask about exactly what heat index is - the bottom line is it’s the impact on the body if the humidity was at a more reasonable, more normal level. Our bodies cool when sweat evaporates off of our skin. In humid weather, sweat doesn’t evaporate nearly as quickly, meaning the body can’t cool nearly as effectively. So a heat index of 102° Monday afternoon in Boston indicates the air will have the same impact on the body as a 102° day with more normal humidity. 

Although Monday afternoon’s atmospheric disturbance aloft isn’t exceptionally strong, it does coincide with a cold front at the ground level. This raises the risk for a few thunderstorms Monday afternoon from 3 p.m. to 8 p.m.

While our exclusive NBC10 and NECN Forecast System shows only a 30 to 40 percent chance of thunder in the Worcester-Providence-Boston corridor, that’s certainly not negligible. The concern is even a few thunderstorms would have plenty of hot and humid air to provide energy for storm development, meaning any of the storms may become strong and damaging. Keep an eye to the western sky, where the storms would move in from, and remember, “when thunder roars, go indoors.” 

The weather quiets overnight Monday night. Less humid air will arrive by dawn for a much more pleasant Tuesday, even as temperatures rise through the 80s to near 90 by the afternoon.

Humidity should remain pretty comfortable Wednesday, though as humidity starts to increase late in the day and toward evening the chance of showers and thunder rises and remains elevated Thursday. 

Right now, it looks like comfortable, less humid air will arrive in time for the upcoming weekend for what appears, at least right now in our exclusive First Alert 10-day forecast, to be a delightful weekend with no storms until a slight chance late Sunday. Humidity may rebuild into the first half of next week, with a returning chance of thunder.

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