Heat wave could break record

Seattle is in for an unusually long and oppressive heat wave this week, with peak temperatures on Wednesday that could break Seattle's all-time record of 100 degrees.

"In short, we are about to enter an historic heat wave for our region," Clifford Mass, a University of Washington atmospheric-sciences professor, wrote on his blog. "One day, your grandchildren will ask you ... did you really experience the temperatures of July 29th, 2009?"

The National Weather Service is forecasting a high temperature of 99 degrees for Wednesday, beating the 95-degree record for the day and just one degree away from Seattle's overall record.

The UW is forecasting triple-digit temperatures using a forecasting program called Probcast, developed by university researchers in atmospheric science, statistics and psychology. The Weather Service uses Probcast, as well as several other systems, for its official forecasts. Doug McDonnal, forecaster at the weather service, said Probcast's 102-degree temperature is the highest prediction of all systems.

Temperatures reached 94 degrees Monday, according to the weather service. Today should be about the same, and each day through Friday is expected to break 90 degrees.

Multiday heat waves are rare in Seattle, where marine air usually moves in and dramatically cools things off, according to the weather service. The last five-day stretch was in 1981.

Giant pockets of low-pressure air are anchored over Hudson Bay and western California, keeping stagnant, hot air stationed over Western Washington.

"There's no end in sight right now," said weather-service meteorologist Johnny Burg.

Temperatures are expected to stay in the 80s through the weekend.

King and Pierce counties have designated public libraries and other community facilities as cooling centers for residents to escape the high temperatures.

Auburn, Federal Way and Bellevue have offered their community centers and libraries as cooling centers as well.

Seattle City Light also advises residents to limit the use of electronic appliances as much as possible, since high temperatures can strain electrical equipment.

Lindsay Toler: 206-464-2463 or ltoler@seattletimes.com