There's now a five-day warning from the National Weather Service.

"The eastern slopes of the Cascades, including Wenatchee, is under an excessive heat warning right now, and that stretches south all the way to the Oregon state line, which includes Moses Lake, Yakima, Pasco," said National Weather Service Meteorologist Charlotte Dewey.

The rest of Eastern Washington is under an excessive heat watch.

The alerts are in place from 11am Monday through 11pm Friday, with highs reaching 110 by Thursday.

Dewey says the Weather Service has seen the hot spell coming for several days, but the confidence level for excessive heat over an extended period wasn't realized until late Sunday.

"It's going to be a prolonged period of very hot temperatures, well above normal." Dewey said. "The normal high temperature for the Wenatchee area is about 90-92 degrees, and so we're looking 10 to 15 degrees above normal."

There's not much concern about high winds during the heat spell. Dewey said there could be some wind gusts Tuesday afternoon, but they'll occur at elevations where the heat warning will not be in effect.

There's concern for fire danger heading into next weekend, when cooler temperatures will be brought in by a change in the weather pattern that is normally accompanied by higher winds.

Dewey said the Weather Service will be monitoring the current weather pattern to determine if the excessive heat warning and watch needs to be extended.

She also warned that overnight lows will not cool off enough to bring any relief to people who don't have air conditioning. Overnight lows during heat spell will only drop to the mid and upper 70's.