Heat and humidity reach one peak Thursday, with another expected Sunday – each of the days sporting temperatures into the 90s with dew point temperatures measuring the amount of moisture in the air reaching oppressive values in the 70s, boosting heat index values to around 100°. In addition, Thursday brings a severe thunderstorm threat during the afternoon and evening from northwest to southeast across New England, though areas south and east of a line from Boston to Providence will probably wait until evening before any storms arise. The heat isn’t a new story, but does reach a new impact on the body Thursday, reaching dangerous levels for some, making hydration, breaks in outdoor activity and respites in air conditioned places all the more important. Heat index is often referred to as “feels like temperature,” measuring impact on the body, and represents the body’s decreased ability to cool in hot and humid conditions. Our bodies are able to cool by sweating, but more specifically, when sweat evaporates the body cools. With abundant humidity, sweat doesn’t readily evaporate off the body and therefore isn’t as effective at cooling, meaning, under normal humidity conditions, the temperature “might as well be” the heat index value. From an atmospheric perspective, the abundant heat and humidity provides ample fuel for thunderstorms to erupt as an energetic disturbance aloft couples with a surface cold front to focus storm development from northwest to southeast during the afternoon and evening. Incoming dry air aloft will couple with increasing elevated wind to promote swaths of damaging wind gusts in Thursday thunderstorms, prompting severe thunderstorm warnings – be ready to seek shelter if storms threaten your community. Keep in mind lightning doesn’t prompt a severe thunderstorm warning like wind and hail do, so remembering “when thunder roars, go indoors,” helps to keep folks safe from regular, non-severe thunderstorms. Scattered storms will slowly wane overnight Thursday night and less humid air arrives for Friday and Saturday but the heat continues. Although storms won’t be commonplace Friday and Saturday, isolated storms certainly are possible just about anywhere in New England in the intense heat. An increasing south wind Sunday will bring a return of oppressive humidity, heat index values around or over 100° and perhaps some scattered afternoon or evening thunder. More widespread showers and thunder are expected Monday as a cold front “breaks” the heat – we use that term cautiously as temperatures will still reach 85 to 90 degrees for daily highs most of next week in the exclusive First Alert 10-day forecast!