Cool air from the Pacific Ocean will deliver some needed relief to parts of western Washington and Oregon later this week following an intense and record-setting burst of heat that kicked off the month of July. However, as the weather pattern evolves this summer in the West, heat will ramp up and stick around over much of the interior Southwest, AccuWeather meteorologists say.
The heat will peak on Wednesday along the Interstate 5 corridor in Washington and Oregon, with temperatures challenging the daily record high of 91 degrees Fahrenheit in Seattle and likely breaking the record high of 96 in Portland, Oregon. Temperatures will then gradually lower into Saturday, according to AccuWeather Meteorologist Brandon Buckingham.
“A timely reprieve from record-challenging heat is in store across the Pacific Northwest late this week and into the weekend,” said Buckingham. “In addition to the cooler conditions, smoke from forest fires in western Canada will shift out of places like Seattle and Portland, resulting in a welcomed improvement in air quality.”
Temperatures will peak in the upper 80s in Seattle and the lower 90s in Portland on Thursday. By Saturday, highs are projected to be right at the historical average – in the mid-70s – in Seattle. The high in Portland for the first day of the weekend will be in the lower 80s, which is just a few degrees above the historical average for the date.
However, from the eastern slopes of the Cascades to the western slopes of the Rockies, a northward bulge in the jet stream will hang on from this weekend to the start of next week. Widespread highs in the 90s are in store for locations such as Spokane, Washington, and The Dalles, Oregon. At this level, temperatures will be 5-15 degrees above the historical average.
A dip in the jet stream may allow a front to sweep through with cooler air during the middle of next week over the interior Northwest. The front would tend to trim temperatures back by 5-10 degrees or more from eastern parts of Washington and Oregon to Idaho for a time next week.
Buckingham noted that a surge in heat could occur once again during the middle of July over much of the Northwest.
No major reprieve is likely for areas farther south in the interior West over the next few weeks. Instead, heat will build, forecasters say.
“A northward bulge in the jet stream that is already in place over the interior Southwest this week will build during mid- to late July,” said AccuWeather Lead Long-Range Meteorologist Paul Pastelok.
This action will translate to even hotter conditions near the ground.
Las Vegas recently set a record for consecutive days in which the high temperature did not reach 100 degrees. The streak reached 294 days after beginning back on Sept. 9, 2022, and ending on Thursday, June 29, 2023.
The historical average high in Las Vegas in early July is in the low 100s. High temperatures will hover around 102 to 106 degrees through this weekend. By next week, temperatures may peak in the 110s on a consistent basis as the jet stream bulge and the associated large area of high pressure strengthen.
Phoenix has already had eight days with high temperatures in the 110s through Tuesday, and plenty more are on the way. Provided spotty thunderstorms do not erupt and cool or moisten the local environment, it is possible that the major metro area will approach 120 degrees Fahrenheit during mid- to late July. The all-time record high for Phoenix is 122 and was set on June 26, 1990.
Salt Lake City has the potential to hit the 100-degree mark in the pattern. The city reached triple digits on July 3 for the first time this year with a high of 101. The historical average high for this time of year in Utah’s capital city is in the mid-90s.
AccuWeather’s long-range forecasting team will be closely monitoring the extent of the heat over the Southwest.
“At this time, it appears the core of the heat will be centered farther to the west and from west Texas to the California deserts,” Pastelok said. “This is much farther west than the heat dome that set up over more densely populated areas of central and eastern Texas and Oklahoma and the lower Mississippi Valley in late June to the start of July.”
AccuWeather’s long-range forecasters still have some concerns about the magnitude of the heat and its impacts on the electrical grid in the Southwest and Texas moving forward this summer, especially if that extreme heat expands farther to the east into more densely populated areas.
The ongoing building heat and dryness in the region will bring spikes in fire danger, especially in wooded areas of northern Arizona and New Mexico in the coming weeks.
The more western position of the jet stream bulge, and a high-pressure area may continue to suppress the North American monsoon in Arizona, western New Mexico and southern parts of Nevada and Utah in the short term.
The position of the high-pressure area over the interior Southwest should allow a continuation of marine air to keep temperatures in the comfortable range along the coast of Southern California for at least the next couple of weeks with highs expected to range from the upper 60s to the mid-70s.
Highs in downtown Los Angeles will be in the 70s to near 80 most days through the weekend with a warming trend possible next week.
Produced in association with AccuWeather
Edited by Alberto Arellano and Joseph Hammond
