Dangerous Heat Arrives Late Week- The "Why" Behind It

A slight reprieve in hot, humid weather will be in place tomorrow as showers and cloud cover from remnants of Hurricane Barry move in. Scattered showers and thunderstorms are expected through the day on Tuesday, with highs in the upper 70s to lower 80s across the region. Forecast radar for 5pm EDT Tuesday is shown below.

However, the relief won’t last long, as the hottest air of the season arrives the second half of this week! High temperatures will reach the mid-upper 90s across the Ohio Valley/Great Lakes Thursday through Sunday, and potentially into early next week as well. Below are forecast high temperatures from the GFS model:

With high humidity also in place to end the week, heat indices will be driven to 100-110 degrees, with localized higher heat indices to 115 degrees. This is dangerous to deadly heat; make sure to stay cool and hydrated! The same four days of heat indices from the GFS model are below:

So what’s causing this heat? Your first reaction may be to call it “global warming” or “climate change”, but it can be explained by a few “normal” atmospheric conditions. First, we have an upper level ridge pumping in hot air across the central United States. With the upper level ridge in place, precipitation and cloud cover is shoved northward into the Upper Midwest. Therefore, sunny to mostly sunny skies also aid in warming up temperatures. Second, high pressure at the surface brings in stable, sinking air, which also keeps skies sunny, conditions dry, and reinforces the hot air in place. Lastly, southeasterly winds will continue to pull warm, moist air into the Ohio Valley and Great Lakes region from the Gulf of Mexico.

These conditions combined will aid in extremely hot weather and potentially dangerous conditions. Several National Weather Service offices have already begun issuing Excessive Heat Watches (burgundy) across the region, and I expect these to become more widespread in the next 48 hours. If you must be outside for prolonged periods during the aforementioned time frame, drink plenty of water and take several breaks in the shade or air conditioning!