Friday marks the start of an unprecedented heat wave in Portland. The temperature will reach a high of around 93 degrees in the area today, gearing up to increase by as much as 10 degrees on Saturday.

The National Weather Service says an abnormally strong high pressure system will move into the Pacific Northwest region over the weekend and into early next week to bring a stretch of hot and dry weather, which will likely break several temperature records.

An excessive heat warning is in effect for much of the Willamette Valley and southwest Washington through Monday.

The good thing about this hot airmass is that humidity will be low, so the heat index will be very similar to the actual temperature forecast.

South Washington and north Oregon’s coastal zones have been added to the excessive heat warning for Sunday, which could be bad news for those planning to take refuge in the water at the coast over the weekend.

The truly hot weather kicks in Saturday. Expect clear skies and temperatures as high as 105. The weather service says no part of the state, other than the coast, will escape the heat. Temperatures of 100 to 105 are likely along the Interstate 5 corridor from Kelso to Cottage Grove. Temperatures will also be in the 100s on both sides of I-84 through the Columbia River Gorge and into northeastern Oregon.

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Even the Cascades will be warm, with highs in the upper 80s likely at pass levels.

Overnight lows won’t cool much in the metro area, with temperatures likely to fall only into the upper 60s to low 70s. That will help create another hot day Sunday, when Portland could see a high of 109. The all-time record high temperature logged at the Portland International Airport is 107, set a few times since 1940. Sunday may very well set a new heat record in many locations across the state.

Long-term forecasts are showing a temperature decrease of a few degrees Monday, but highs will likely still be in the 100s. Tuesday’s high is expected to drop back into the 90s.

A system will travel northward off the coast to bring a slow cool down to the region through next week, but temperatures will remain 10 to 20 degrees warmer than average for late June and early July.