United States

By Anthony Sagliani, Meteorologist

August 17, 2012; 5:08 AM

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Summer has certainly been hard to come by this year for most of western Washington and Oregon. For more than two months, the temperature failed to hit 90 degrees or more for both Portland and Seattle.

That changed drastically once early August rolled around, and temperatures for both cities are running nearly 4 degrees above normal for the month.

During the last few days, incredible heat has gripped much of the region. Portland has already had two days above 100 degrees this month. The last time the temperature rose above 100 degrees twice in one month was July 2006.

Meanwhile, Seattle has been baking in the searing sun as well. The average number of days above 90 degrees for the Emerald City is two. For the month of August so far, there have already been three days and Friday will in all likelihood be day number four.

The reason for this extreme heat is the position of the jet stream, a thin ribbon of air miles high that typically has cool air to its north and warm air to its south.

For much of the summer, the Northwest had been stuck in a dip in the jet stream with cool temperatures and unsettled weather. Farther east over the Nation's Heartland, a strong ridge in the jet stream allowed for severe drought and relentless heat.

The pattern changed in early August as the ridge moved over the West. As the jet stream climbed well north of the Canadian border, so did the hot weather.

A cooldown is expected across the region beginning this weekend as temperatures drop to more normal levels for late August as winds bring cooler air inland off the ocean.

Highs will be 10-20 degrees lower and they will even struggle to reach 80 degrees by Sunday.

Stay with us here at AccuWeather.com for all the latest on this record heat wave and the cooldown to arrive this weekend.