12 August 2016
A weekend of brutal heat is on the way, from here on Delmarva, to DC, and all the way to New York, with heat index values well above 100. Extreme humidity covers much of the Eastern half of the U.S. this Friday evening, and the high moisture content of the air is pushing heat index values into the danger range. The levels of water vapor in the atmosphere are also keeping the nights exceptionally warm, and this increases the risk of heat illness, since those with no air conditioning get no relief at night.
The weekend will bring more of the same with model guidance this afternoon indicating heat index values near 110 from the Delmarva area, all the way to Long Island, and into Connecticut.
The images (below) show the predicted heat index based on the NOAA 4 km resolution WRF model. This model does a good job of predicting these values, and I’m quite confident that this is about what we will see.
The long range guidance shows the storm-track (500 hPa wind flow) easing into an almost early fall like pattern, which should bring the heat down, and the rain chances up, over the NE third of the U.S. The image below is an average of several different model runs. It shows the upper level high weakening and moving into the Atlantic.