With the high heat comes high humidity.The key with respect to how hot it feels will be just how moist the air remains through the day. On Friday in the Mid Atlantic, winds are forecast to pick up a bit towards
the afternoon hours and remain more out of west direction, which would promote more atmospheric mixing. This mixing will allow the dew points to drop during times of peak heating; the dew points should fall enough to keep the heat index values below 100 for Friday. However, the mixing will fade away, setting the stage for a very hot and humid weekend.
An upper ridge will build across the Middle Atlantic states later Friday and Saturday and then remain across the region into early next week. Dew points will begin to creep up later Saturday with excessive values expected on Sunday. This means that heat index values, which combine heat and humidity, will be in the mid/upper 90s Saturday and in the upper 90s and low 100s for Sunday across the I-95 corridor from Washington, DC to Boston, MA, with some of the worst heat index values between Baltimore, MD and Philadelphia, PA.
While the heat is on, little in the way of rain is expected this weekend. A small chance of showers and storms will exist along the eastern U.S. on Monday with a greater chance of rain during the middle part of the new week. The next threat of rain will be dependent on how fast the ridge responsible for this hot blast lingers and how much upper level energy is able to move into the Mid Atlantic and Northeast.
