A brutal heat wave is scorching the Northwest.

Following previous punishing heat waves in the Southwest and East, folks in northern California and western portions of Oregon and Washington are enduring blistering temperatures, some of which are shattering records.

"The current heat wave in the Northwest may end up being the most notable event of the entire summer for the U.S.," AccuWeather meteorologist Elliot Abrams said.

The intense heat will threaten human health, potentially cause power blackouts and exacerbate the spread of wildfires. Light-rail trains in Portland on Wednesday operated at slower speeds amid worries that the heat would force tracks to expand and cause a derailment.

Portland recorded a new daily temperature high Wednesday, hitting 99 degrees at 2:30 p.m., according to the National Weather Service in Portland. The previous record for Aug. 2 was 96 degrees set in 1986.

Medford, Ore., on Tuesday climbed to a daily record high of 110 degrees.

The National Weather Service somewhat amended its earlier forecast for Portland to break its record high of 107 degrees — the hottest day since records began in January 1874, during the Grant Administration about 52,000 days ago. Portland is now looking at a high of 107 degrees on Thursday, which would match the record.

“With little to no cloud cover at night, the higher temperatures kind of hang around a little bit,” meteorologist David Bishop told the Associated Press. That creates a cycle in which “the next day is going to be a little bit warmer because we’re already starting off warmer than the previous day.”

Portland's average high temperature in early August is 82 degrees. The Weather Channel, meanwhile, forecasts a high of 109 degrees Thursday in Portland, which would surpass the all-time record.

Other cities in Oregon that could see all-time highs include Eugene, Medford and Salem.

Cities and counties across the Portland area have announced locations and hours for cooling centers, KGW-TV said.

Smoke from wildfires in British Columbia is adding to the weather headaches across the Northwest.

It's even too hot to sell ice cream, one Portland vendor told KGW. "When it gets too hot, the cone starts to drip and people would rather hide inside in the shade," laughed Scoop Ice Cream owner Sean Sitton. When he saw the forecast, he decided to close Wednesday and Thursday.

Excessive heat warnings are in effect in Seattle and Portland through Friday. The heat will create "a dangerous situation in which heat illnesses are possible," the National Weather Service said.

The latest forecast for Seattle said the high for Thursday would be 94 degrees. Seattle's average high temperature this time of year is a mild 77 degrees. Seattle-based meteorologist Cliff Mass called these forecasts "crazy warm" on his blog.

According to the weather service, "there could be some air quality concerns, which can occur with very hot weather as ozone and other pollutants increase."

What often makes the heat more intolerable in cities such as Portland and Seattle is the lack of air conditioning.

"My biggest surprise today was seeing some unsold fans in my local supermarket," Mass wrote on his blog Monday. "I bet they will be gone in two days."

Even if no all-time record highs are set, many locations should see record highs for a specific date.

Northern California and western Nevada will also see scorching temperatures, with many spots at or above 100 degrees. Redding, Calif., should soar to 113 degrees Wednesday.

The heat is due to "an abnormally strong ridge of high pressure," AccuWeather meteorologist Dan Pydynowski said. Air sinks under areas of high pressure, which prevents clouds from forming.

“The ridge should begin to weaken heading into Friday and Saturday,” Pydynowski said. “So while it will still be very warm with above-normal temperatures, the record-breaking heat should come to an end."