The extreme heat wave responsible for sending temperatures in some locations to their highest level on record this week will soon ease across the northwestern United States.
"A northward bulge in the jet stream, an area of high pressure at the surface, intense sunshine and dry soil conditions are responsible for the extreme heat," according to AccuWeather Senior Meteorologist Brett Anderson.
The jet stream is a fast river of air at the level in the atmosphere in which jets cruise. The jet stream separates heat to the south from cool air to the north.
High pressure is a large area of sinking, dry air that spins in a slow clockwise direction. The sinking air heats up as it descends through the atmosphere. The stronger the area of high pressure, the greater the amount of heat is produced.
Temperatures are projected to trend downward slightly on Friday, but the more noticeable change will occur this weekend.
"By this weekend, the jet stream will straighten out, and the area of high pressure will weaken," Anderson said.
Interior locations will still be hot during the midday and afternoon, just not as extreme as much of this week.
"Temperatures on Saturday and Sunday will throttle back between 5 and 15 degrees Fahrenheit, when compared to most days this week across much of Washington, Oregon and Idaho," Anderson said.
Highs in the 110s will be replaced with highs near 100 across the interior hot spots. Highs near or above 100 over the rest of the interior will be replaced with highs in the 90s.
In some coastal locations of Washington and Oregon, highs will trend back to the 70s and lower 80s.
Farther south, in Northern California and Nevada, it may take until the middle of next week before temperatures lower significantly.
People should continue to limit strenuous activity during the midday and afternoon hours. Be sure to drink plenty of fluids.
The pattern change will reduce the demand for electricity, and air quality may improve as well.
However, the risk of wildfire ignition and spread will remain elevated, due to the low chance of shower and thunderstorm activity.
As of Tuesday, Aug. 1, more than 20 wildfires were burning the the three-state area of Idaho, Oregon and Washington, according to the Wildfire Incident Information System. These active fires have consumed more than 265,000 acres.
Officials urge residents and visitors to observe all restrictions on the use of open flames.
People using power equipment and cooking outdoors to reduce the buildup of heat in their homes should use caution. Never park over high brush as the heat from the exhaust system can start a fire. Be sure to extinguish campfires prior to leaving the vicinity.
In terms of rainfall, enough moisture may return to the region to produce very spotty thunderstorms next week. However, some of the storms may bring little or no rainfall and may raise the risk of lightning-induced wildfires.
"It is possible that heat may again build for a few days during the second week of August," Anderson said.
The amount and duration of that mid-month heat will depend on the amount of sunshine and moisture in the region as well as the behavior of other weather systems across North America.