Lehigh Valley under excessive heat warning Wednesday for heat index values up to 105; storms possible this evening

The Lehigh Valley is under an excessive heat warning as heat index values are expected to exceed 100 Wednesday.

The National Weather Service placed Lehigh and Northampton counties under the warning until 8 p.m. In their warning, forecasters wrote that there will be “dangerously hot” conditions, with heat index values up to 105.

The Allentown area is expected to reach those values between 2 p.m. and 4 p.m.

The weather service said heat-related illnesses increase significantly during extreme heat and high humidity events. The greatest heat index values will occur in and around lower elevations and valleys, forecasters said.

Residents are encouraged to drink plenty of fluids, stay in an air-conditioned room, stay out of the sun and check up on relatives or neighbors. Those working outside should take frequent breaks.

Wednesday will be the sixth day in a row of temperatures reaching the 90s. The warmest day of the month so far was Tuesday, which had a recorded high of 95. The hottest day of the year for the Lehigh Valley was on June 22, which had a recorded high of 98, according to weather service data.

Outside of extreme heat, forecasters said there could be a few thunderstorms north and west of the Interstate 95 corridor in the Lehigh Valley, Poconos and northern New Jersey. The main concern with those storms is heavy rain. Any storms that come through the area should be fast-moving, according to forecasters.  There could also be severe thunderstorms that could bring wind damage, the weather service said.

Temperatures will be a little cooler Thursday and Friday. The weather service is expecting highs of 90 Thursday and 86 Friday. There is also a chance of rain over the weekend. Here is the extended forecast from the National Weather Service:

Thursday: A slight chance of showers and thunderstorms between 8 a.m. and 11 a.m. Mostly sunny, with a high near 90. Southwest wind around 10 mph. Chance of precipitation is 20%.

Thursday Night: A slight chance of showers and thunderstorms after 2 a.m. Partly cloudy, with a low around 70. West wind around 5 mph becoming calm after midnight. Chance of precipitation is 20%.

Friday: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 2 p.m. Partly sunny, with a high near 86. Calm wind becoming southwest around 5 mph. Chance of precipitation is 60%. New rainfall amounts between a quarter and half of an inch possible.

Friday Night: A chance of showers and thunderstorms. Mostly cloudy, with a low around 70. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Saturday: A chance of showers, with thunderstorms also possible after 2 p.m. Mostly sunny, with a high near 92. Chance of precipitation is 30%.

Saturday Night: A chance of thunderstorms before 8 p.m. Mostly clear, with a low around 69. Chance of precipitation is 30%.

Sunday: Sunny, with a high near 95.

Sunday Night: Mostly clear, with a low around 72.

Monday: Sunny, with a high near 95.

Monday Night: Mostly clear, with a low around 74.

Tuesday: A chance of showers and thunderstorms. Sunny, with a high near 96. Chance of precipitation is 30%.