The 'Thunder Balk' Heard 'Round The Ballpark

August marks the final full month of summer, and this year it looks like there will be a sweltering conclusion for many in the Lower 48, especially east of the Rockies.

Temperatures are forecast to be the most above average in August for a vast area that stretches from the Plains and Midwest into portions of the Northeast, according to the latest update from The Weather Company, an IBM Business, and Atmospheric G2. The forecast has trended hotter for a more expansive area in those regions when compared to the initial outlook issued earlier in the month.

"The combination of a strong La Niña base state, historically-strong persistence and ongoing/building drought across the western/central U.S. suggest a hot August is a slam dunk," said Todd Crawford, director of meteorology at Atmospheric G2.

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Most other locations, including the coastal Southeast and much of the West Coast, are forecast to see temperatures near or slightly above average. Only a sliver of the Desert Southwest might be slightly cooler than average due to monsoon thunderstorm activity holding temperatures down.

A shift in the large-scale weather pattern will help ring in this hot pattern east of the Rockies right as the month begins.

July ended with a dome of high pressure bringing a prolonged heat wave to the Northwest. Meanwhile, parts of the Northern Plains, upper Midwest and Great Lakes have seen temperatures that are relatively tolerable for mid-summer because of a southward plunge of the jet stream

That setup will completely flip in August's first week and allow expansive high pressure to bring heat back to much of the central and eastern states. The Northwest will cool off at the same time as a southward plunge of the jet stream sets up over that region.

Moving Past The Typical Hottest Time Of Year

The average peak of summertime heat varies across the Lower 48, but for the majority of Americans, it happens in July or early August. This is shown in the map below from NOAA, which displays when the average hottest day of the year happens based on data from 1991 to 2020.

Early to mid-August tends to be the hottest time for parts of the South from central and eastern Texas into the Ozarks and lower Mississippi Valley.

By that time, the somewhat daily slow-moving thunderstorms of early summer give way to more persistent high pressure over the South that suppresses clouds and dries soil, helping temperatures to soar.

Early August is also typically the hottest time along the northern tier of states from northwest Minnesota and North Dakota to parts of Washington state.

Of course, these are just long-term averages. In any given year, bulging areas of high pressure aloft can deliver the year's hottest weather for a few weeks on either side of the average dates.

August's first week could be an example since the previously-mentioned dome of high pressure might bring hot temperatures that are on par with what was seen earlier in summer in the central and eastern states.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.