National heat wave to spare the NW

By Ben Olson
Reader Staff

This week, some of the hottest temperatures of the season will hit across the nation with one notable exception: the Northwest.

“The big high pressure ridge bringing the hot weather is centered over more of the central U.S.,” said meteorologist Randy Mann. “When we’re on the ‘back’ side, we often get the cooler and wetter weather.”

Very high humidity and soaring temperatures are expected throughout the week, with cities like Des Moines, Kansas City, St. Louis, Minneapolis, Oklahoma City and Chicago all expected to see temperatures exceeding 100 degrees F. When you take the humidity into account, the heat index may rise to over 120 degrees F.

When extreme heat is combined with elevated humidity, it can prove especially dangerous. Elevated humidity slows the act of sweating, which is the body’s cooling mechanism.

In 1995, at least 465 people died in Chicago from extreme heat over a five-day period, according to CNN. Hundreds more were hospitalized.

This week, the high humidity mixed with above-average temperatures combined to create a ridge of high pressure known as a “heat dome” over the central U.S. High pressure acts as a lid on the atmosphere. When hot air tries to escape, the lid causes it to sink and the air is forced downward, warming even more.

Another factor that has contributed to this dangerous heat wave is known as “corn sweat.” Corn releases water from the leaves, and when wind sweeps through, moisture is released into the atmosphere causing humidity levels to soar in surrounding areas.

In contrast to the rest of the nation, North Idaho should expect temperatures this week to hover in the 80s, with a few days possibly running into the 90s. But, Mann pointed out, we should feel some residual effects of the heat wave in the latter part of July.

“The high is expected to expand and give us some warm weather for the rest of July,” he said.