MINNEAPOLIS, MN — A "heat dome" is building over Minnesota, and the National Weather Service says its effects will be felt across the Twin Cities for the better part of a week.
A heat dome forms when a strong area of high pressure parks itself over a region and traps warm air underneath, acting almost like a lid.
Sinking air beneath that high pressure compresses and warms further, adding to the heat, while the high pressure also blocks storm systems from moving through.
That combination is what produces the dome's signature effects: long stretches of dry, sunny weather, temperatures that build day after day rather than spiking once, and little relief overnight since the trapped heat has nowhere to go.
The clearest effect will be on daytime highs. Temperatures are forecast to climb from 84 on Thursday to 87 Friday, 89 Saturday, 92 Sunday, 91 Monday and 92 Tuesday at Minneapolis-St. Paul International Airport, according to the weather service.
Heat index values, which account for humidity, are expected to climb into the mid to upper 90s during that stretch. Some Minnesota communities could see actual air temperatures near 95 to 97 degrees.
The dome's other defining effect is dryness. With the high pressure blocking storm systems, the only meaningful rain chance in the entire seven day stretch comes Friday afternoon in central Minnesota, forecasters said.
Scattered showers and storms are possible tonight farther south and east, across southern Minnesota and western Wisconsin, before that drying pattern sets in.
Forecasters have cautioned that some computer models predicting highs of 100 degrees or more for several consecutive days may be overdone, noting that the Twin Cities has recorded triple digit heat only 67 times since 1871, and just six of those instances have come since 2000.
Minnesota sits at the center of the heat dome in the latest outlooks from the Climate Prediction Center, which show the highest odds of above normal temperatures nationally centered over the Upper Midwest for the July 14 to 18 window.
That bullseye shifts north into Montana and North Dakota for the following week, July 16 to 22, an early sign that the dome's grip on Minnesota could begin to loosen even as temperatures remain above normal.
The first real sign of relief is expected Wednesday, when highs are forecast to ease back to near 89, according to the latest forecast.
The weather service is not currently reporting any watches, warnings or advisories for Minnesota or Wisconsin.
Check out the full NWS forecast from the MSP Airport below:
Friday: Mostly sunny, with a high near 87. Calm wind becoming south around 5 mph in the afternoon.
Friday Night: Partly cloudy, with a low around 69. South wind 5 to 10 mph.
Saturday: Sunny, with a high near 89. South wind 5 to 10 mph.
Saturday Night: Mostly clear, with a low around 70. South wind around 10 mph.
Sunday: Sunny, with a high near 92. South southwest wind 5 to 10 mph.
Sunday Night: Clear, with a low around 70. South southwest wind around 10 mph.
Monday: Sunny, with a high near 91. South southwest wind 10 to 15 mph.
Monday Night: Mostly clear, with a low around 71. South southwest wind around 10 mph.
Tuesday: Sunny, with a high near 92. West southwest wind 5 to 10 mph.
Tuesday Night: Mostly clear, with a low around 71. South southwest wind 5 to 10 mph.
Wednesday: Sunny, with a high near 89. Southwest wind 5 to 10 mph.
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