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Coast-to-coast heat dome expected to deliver sweltering weather next week

Summer is supposed to be hot. But this season has featured many large-scale North American heat waves that have roasted significant swaths of the country, helping temperatures skyrocket and toppling records.
Another heat wave is set to park over the Lower 48 next week, bringing anomalous summertime heat to parts of the central and eastern United States that may have missed out on previous events. 

Early estimates indicate that most of the contiguous United States will see highs running 10 to 15 degrees above average. When combined with climbing humidity, it'll feel as if it's well into the triple digits for millions. The pattern could also spark severe thunderstorms, perhaps packing strong winds, that could roll through the northern Great Lakes and New England during late July and August.

On Thursday, most of the heat was relegated to the western United States, where temperatures in Montana were forecast to climb into the 100s.

Billings, Mont., has already measured 12 days topping 95 degrees this month. With highs in the upper 90s to lower 100s projected every day over the coming week, it is possible that tally may climb to near 20 by the end of July. That would mark the most 95-plus degree days in Billings in July since 1936.

Excessive heat warnings are in effect for most of eastern Montana, where temperatures could increase the risk for heat-related illnesses. Some relief is on the way - but not much.

"Tonight's cold front will bring very modest 'cooling' for Friday, with highs tomorrow in the 90s," wrote the Weather Service in Billings.

By Friday and Saturday, that heat will shift east, bringing highs in the upper 90s to near 100 to the Dakotas this weekend. That's just an appetizer, however. The main heat event, which will occupy a much larger swath of the western and central United States, will just be getting started by then.

On Monday and Tuesday, attention turns to the Pacific Northwest and northern Intermountain West, where a renewed batch of heat will begin to gather. That batch represents the first signs of a building heat dome that will drape itself across most of the Lower 48 by midweek.

On Wednesday, the heat dome should stretch from the Pacific Coast to the Appalachians, with hazy and hot temperatures just about everywhere in between. The National Oceanic and Atmospheric Administration's Climate Prediction Center indicates odds of near average to above average temperatures for the entire contiguous United States.

It's too early to give specific numbers, but the Plains could see temperatures in the mid-to-upper 90s or lower 100s as the heat wave builds, with mid-to-upper 90s in the Southeast and many areas topping 100 in the West.

Heat domes are zones of high pressure that deliver sinking air, which warms and dries as it subsides. A heat dome can also help bring clear skies, while deflecting clouds and storm systems around it. That allows for additional sunshine, reinforcing heating.

While nearly everyone will be basking in summertime toastiness, a few areas will trend closer to average. Early week monsoonal moisture may linger over the Desert Southwest and Four Corners region, keeping temperatures a bit more modest as afternoon showers and thunderstorms brew.

Another area to watch that may not fully tap into the heat will be parts of New England. Computer weather models hint that a lobe of cool air may hang around at high altitudes, keeping surface temperatures closer to average. In between there and the heat dome, a corridor of thunderstorm activity may crop up; the jet stream pattern would favor strong winds.

The greatest risk for strong to severe storms during this period would be from the northern Tier and Upper Midwest through the Great Lakes region and into the Northeast.

While heat domes are normal staples of the summer, the duration and intensity of said heat events is on the rise in tandem with warming global temperatures thanks to human-induced climate change.

Just last month, a thousand-year heat event that would have been "virtually impossible" without climate change brought temperatures of 108 degrees to Seattle and 116 degrees to Portland, Ore. Lytton, British Columbia, broke the Canadian national temperature record three days in a row, hitting 122 degrees before the town burned down in a cataclysmic wildfire.

Meanwhile, much of the United States has spent days veiled by a layer of wildfire smoke poured into the skies by hundreds of blazes in western North America, including the 400,000-acre Bootleg Fire in southeastern Oregon. Climate change continues to accelerate drought conditions taking hold of the West, fostering more favorable fire conditions and more extreme wildfire behavior.

 

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