Portland, Oregon has been suffering through one of the worst heat waves in it’s recorded history. The official reporting station, at Portland International Airport, has recorded high temperatures, at or above average, every day since June 3rd.

The cause for all the heat in the Portland area, and for much of the western third of the country,: a persistent and vigorous ridge of High Pressure had set up over the West Coast, as the jet stream lifted northward into Canada.

Relief for the Portland area, and the rest of the Pacific Northwest, may be on the way. A cut-off low, a pocket of colder air aloft that has separated from the jet stream, will arrive onshore, and will be drawn back into the jet stream. As it does so, it will help to pull the jet stream down, allowing cooler air to flow into the Northwest.
Highs in the low 90s will finally disappear from the forecast, as temperatures for the upcoming weekend will sink back to the low 80s, which is around the seasonal average of 79-80° for this calendar week. It is hard to believe that the high temperature for Portland on June 2nd was only 62 (the average high temp for that day is 71). For reference, on average, daytime highs in the low 60s, are typical of mid October.

Source: WeatherNation Portland: One of the Worst Heat Waves in History – Relief in Sight? | For WeatherNation: Meteorologist, Jason Cerjak