August is just around the corner, and Mother Nature is getting ready to kick it up a notch. At least 30 million Americans will see highs hit 100 degrees or greater over the next week or so as a sprawling heat dome parks itself over much of the Lower 48.

Temperatures won’t be off the charts – in most place they’ll range between 5 and 10 degrees above average. But the long-duration heat will combine with high levels of humidity in some areas to yield heat index values well into the triple digits, spiking to hazardous levels in spots. Heat advisories and excessive heat watches blanket much of the central U.S..

Around the periphery of the stagnant heat dome, heavy thunderstorms are a concern, in the Southwest as well as the Great Lakes and Northeast.

While storms generated by the Southwest monsoon have brought welcome moisture to the drought-plagued region, they’ve also unleashed flash flooding and blinding sandstorms, including one blamed for eight deaths in Utah.

The overarching weather pattern is also one conducive to triggering vigorous thunderstorms in the Great Lakes and Northeast this week, which pose a damaging wind threat.

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On Monday the heat will organize over parts of the northern Intermountain West and Northern Tier, where highs top 100 degrees in Boise, Billings, Mont. and Bismarck, N.D.


Over the coming days, the heat will swell over the northern Plains as a ridge of high pressure builds and shunts the jet stream into Canada. That will make for a large bubble of clear skies and sinking air – the perfect recipe for light winds, toasty temperatures and scorching sunshine.

Excessive heat watches span the Upper Midwest and Corn Belt, including cities like Minneapolis, St. Paul and Des Moines.

“Extreme heat and humidity will significantly increase the potential for heat related illnesses,” warned the Weather Service in the Twin Cities. They also noted that overnight lows will struggle to fall much below the mid-70s, providing little nocturnal respite from the heat. That’s integral to the body’s ability to cool down.

Most of South Dakota, Nebraska, Arkansas, Louisiana and parts of Mississippi, Oklahoma and Texas are encompassed in heat advisories. Dew points, a measure of how much moisture is present in the air, will surge to 70 degrees or higher over most of the eastern U.S.. That will bring a sultry, soupy feel to the air.

On Tuesday, the heat dome will be centered over the northern Plains, with temperatures climbing to 106 degrees in Billings and 103 in Bismarck. That’s just two degrees shy of Billings’ all-time record; it will also beat out the daily high of 103 degrees set in 1947. It would also be the hottest temperature ever recorded in Billings so late in the summer.

Omaha, Neb., Kansas City, Oklahoma City and Houston will all peak in the upper 90s on Tuesday; Dallas will nick 100. Midweek temperatures will remain similar, with a slight uptick in readings over the Pacific Northwest as a reinforcing shot of high pressure amplifies the heat dome.


In fact, the atmosphere’s “halfway point” will bulge upwards more than 400 feet above typical, resulting from the hot temperatures expanding the atmosphere vertically. It’s the same premise behind a balloon growing in volume when heated or shrinking when chilled.

The heat will consolidate over the Deep South and Southeast into next weekend.

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The Desert Southwest, notorious for its blistering heat, has seen a reprieve from scorching temperatures in recent days, but has been victim to an onslaught of stormy conditions associated with the seasonal monsoon.

The monsoon – driven by a wind shift which draws moisture from the Pacific over the desert – has been intensified by a pool of cold air at high altitudes over the region since late last week. Towering thunderstorms have dropped curtains of drenching rain punctuated by pinpoint bolts of lightning, leading to funnel clouds, flash flooding and washed-out roadways.

Social media video even captured a vehicle being swept downstream in raging torrents of water that, an hour earlier, had likely been a dry arroyo.

The downdrafts exhaled by thunderstorms over the Desert Southwest have also kicked up sandstorms, or haboobs, that have brought abrupt drops in visibility. One photogenic haboob descended on the Grand Canyon on Friday.


The erratic thunderstorm outflow winds kicked up thick dust that crossed Interstate 15 in Utah on Sunday. Motorists encountered the sudden drop in visibilities and, while some pulled over, others did not. That resulted in a deadly 20-car pileup that claimed at least eight lives. Dry antecedent conditions stemming from longstanding drought in the West was also a contributing factor that allowed for dust to easily be lofted.

While highly disruptive in some areas, the monsoon rains have brought beneficial moisture as far west as Southern California. Los Angeles even received measurable rain Monday, which is unusual in July. The brief soaking was enough to push this month into third place among the wettest July’s on record. Flash flood watches were in effect for much of interior southern California on Monday.

In Phoenix, clouds and rain held high temperatures in the low 80s between Friday and Sunday, the first time it’s been that cool over three consecutive days in July on record. Its average high at this time of year is 106 degrees.

Phoenix has seen 1.84 inches of rain through Sunday due to the monsoon, which is more than all of its monsoon rain in 2019 and 2020 combined.

While thunderstorm activity associated with the monsoon may ease some over the next several days, forecast models do show the possibility of it flaring up some later this week.

So far, little of its moisture has broken through to the north, where it remains exceptionally dry and 86 large wildfires are burning in a dozen states. The largest of the blazes, Bootleg Fire, still is just over 50 percent contained as it continues to rage after having torched 400,000 acres in south central Oregon.


The fires are pouring copious amounts of smoke into the atmosphere, leading to sporadic air quality concerns. That smoke is also riding northwards around the developing heat dome, surfing jet stream winds all the way to the East Coast.

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The northern periphery of the heat dome, sometimes referred to by meteorologists as a “ring of fire,” will also be a breeding ground for thunderstorms, some strong to severe. A weak, diffuse front will exist north of the heat dome, marking the edge of cooler temperatures banked to the north in Canada, along which storms may erupt. The jet stream riding along this transition zone will energize storms, which may produce damaging wind gusts and large hail.

Severe storms are possible in northern Minnesota and the Great Lakes on Monday and Tuesday before expanding into the Ohio Valley by Wednesday. By Thursday, widespread thunderstorms, some severe, could then shift into the Northeast.

The Northeast is one part of the country that looks to remain untouched by the heat dome itself, with temperatures near or even a little below average this week. Indications are that the Northeast will remain on the cool side of the jet stream over the next week to ten days.