Seattle hits 97 today; is 100 on the way?

Seattle hit a high temperature today of 97 degrees, tying a record set in 1998, according to the National Weather Service.

The heat wave might reach its zenith Wednesday when the temperature could break the city's all-time record of 100 degrees.

But that depends...

The National Weather Service initially said the high for Wednesday would be 99 degrees, but early today upgraded that forecast to say it would reach 100 degrees. Today was forecast for a high of 95.

The University of Washington, however, is forecasting triple-digit temperatures using a forecasting program called Probcast, which predicts a high Wednesday of a whopping 102 degrees.

The all-time high temperature of 100 degrees in Seattle was set July 20, 1994.

"In short, we are about to enter a 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 had forecast a high temperature of 99 degrees for Wednesday, beating the 95-degree record for the day.

However, at 4 a.m. today, the Weather Service nudged its prediction upward, forecasting that temperatures in Seattle would reach 100 degrees, according to meteorologist Dennis D'Amico. The National Weather Service also extended the excessive heat warning through Friday.

"We're not going to get a lot of relief," D'Amico said.

He said the overnight low Monday night into this morning dropped to only 69 degrees.

The UW used a program called Probcast for its triple-digit forecast. The program was developed by university researchers in atmospheric science, statistics and psychology.

The Weather Service also uses Probcast, as well as several other systems, for its official forecasts.

Temperatures reached 94 degrees Monday, according to the Weather Service. Today should be about the same, the Weather Service said, with a high of 94 in Seattle and 97 degrees at Seattle-Tacoma International Airport.

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.

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

According to the Seattle Public Library, many, but not all, library branches have air conditioning.

The Central Library in downtown Seattle and the following branches offer air conditioning: Ballard, Beacon Hill, Broadview, Capitol Hill, Delridge, Douglass-Truth, Greenwood, High Point, International District/Chinatown, Lake City, Magnolia, Montlake, NewHolly, Northgate, Rainier Beach and South Park. They are open until 8 tonight.

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 because high temperatures can strain the power supply.

For tips on keeping cool, see http://www.kingcounty.gov/healthservices/health/news/2008/BeatTheHeat.aspx

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