Record heat traps much of U.S. — except here

Seattleites may gripe about the recent patchy sun and cool temperatures, but our clouds have a silver lining, said Jay Neher, a meteorologist for the National Weather Service.

Just look at the heat wave gripping the central part of the U.S.

Seventeen states issued excessive-heat watches on Monday, with a number of upper Midwest states expecting temperatures higher than 105 degrees. The heat wave is sending people to the hospital, damaging roads and causing air-conditioning bills to skyrocket.

In Seattle, however, Tuesday will be partly sunny, with a high of about 73 degrees, according to the Weather Service. On Wednesday and Thursday, it is supposed to be mostly cloudy in the mid-60s, with a 50 percent chance of showers. Friday is expected to be partly sunny, with a high of just 67. The weekend should bring more partial sunshine with highs of around 70 on Saturday and Sunday.

Compare that with what felt like 126 degrees in Newton, Iowa, on Monday; 120 degrees in Mitchell, S.D.; and 119 degrees in Madison, Minn., according to The Associated Press. That is what the heat index was in those places, a measure of how hot it really feels when the relative humidity is added to the actual air temperature.

In Iowa, six people were hospitalized due to heat and humidity as of Sunday, where the top recorded temperature hit 99 degrees over the weekend, about 10 degrees above the average temperature for this time of year.

Brad Colman, the meteorologist in charge at the Weather Service station in Seattle, attributes Washington's cooler, wetter weather to a phenomenon meteorologists call "locking," where the atmosphere locks into a persistent pattern and creates a cycle of relatively unchanging weather.

"In the winter, we had a strong La Niña in the tropical Pacific and a cold winter in the Northwest, which was very consistent with historical weather," Colman said. "Except for a few sunny days in the Northwest, it has been a remarkably persistent pattern."

He mentioned that the Midwest is locked into the weather it's experiencing now and will likely continue through this week.

Neher, of the National Weather Service, says Seattle's summer weather may not be too bad, depending on your outlook.

"If you like heat indexes around 100, you'll be disappointed with our weather," said Neher. "If you don't, you're probably happy to be in Seattle."

On an interstate bridge in Oklahoma City, heat caused steel expansion joints to buckle and rise, which closed two lanes of the highway downtown and damaged some cars.

Temperatures in the city have been unrelenting, with more than 47 straight days of 90-degree-plus temperatures, and 27 so far that have crept into the triple digits.

City officials in Detroit and Chicago, where temperatures are expected to hit 105 degrees, have opened cooling centers to provide residents without air conditioning in their homes a place to stay cool.

A handful of cities set highs records last week. On June 15, Tallahassee hit 105 degrees and Alpena, Mich., sweltered in the high 90s. On June 26, both Borger, Texas, and Gage, Okla., reached 113 degrees.

The sizzling Midwest heat doesn't look to let up this week, but will move east by Wednesday or Thursday, forecasters say. Extreme heat is expected to bake the eastern United States by week's end. Bloomberg News reports that temperatures may reach about 100 degrees in New York this week.

Meanwhile, Western Washington will be one of the few areas with near or below normal temperatures.

Amy Harris: 206-464-2212 or aharris@seattletimes.com