Following record heat into Tuesday, temperatures are forecast to throttle back over the West but with the risk of thunderstorms that may ignite new wildfires later this week and this weekend.
Temperatures will soar well into the triple digits Fahrenheit and challenge record highs on Tuesday afternoon.
Daily record highs were set on Monday at a number of locations over the interior West. These include Palm Springs, Calif., and Phoenix and Tucson, Ariz.
Temperatures will continue to average 5 degrees to 15 degrees above normal until the middle of the week, when a gradual cooldown commences.
The most dramatic downward temperature trend will be in the Northwest and is forecast to be centered on this weekend.
High temperatures near 100 in places such as Salt Lake City; Boise, Idaho; and The Dalles, Ore., will be trimmed by 15 degrees to 20 degrees from their peak early this week to near 80 degrees this weekend.
Poor air quality experienced in some of the interior locations is likely to improve later this week, unless a local area is downwind of a distant wildfire.
Even in Phoenix and Las Vegas, highs close to 115 degrees from Monday and Tuesday will be trimmed to near 100 by this weekend. In Seattle and Portland, Ore., highs within a few degrees of 90 will be replaced with highs in the 70s.
Meanwhile, in immediate coastal areas from San Francisco to Los Angeles and San Diego, little temperature chance is likely from day to day through this weekend.
Heat, cooldown pattern explained
The main cause of the higher-than-average temperatures at the start of this week has been due to a northward bulge in the jet stream.
This northward bulge represents warm air aloft. When the air is warm at the jet stream level, the air near the surface has a much easier time heating up.
Late this week and this weekend, the jet stream is forecast to plunge southward.
During the southward plunge, the upper atmosphere will turn colder.
This time of the year, when the air aloft is chilly, the August sun still heats the ground and creates a volatile atmosphere that can trigger an eruption of thunderstorms.
Such a pattern may evolve over parts of the West, especially across portions of Washington, Oregon, Idaho and the northern parts of California, Nevada and Utah this weekend.
Since only a small amount of moisture is likely to be available, the storms may bring little to no rain, but cloud-to-ground lightning strikes, which may ignite wildfires.
Dozens of wildfires were actively burning in the western United States this week, according to InciWeb. These active fires have consumed more than 200,000 acres. A number of these fires were started by lightning strikes.
Another change on the way next week
Meanwhile, the pattern into the weekend will continue to allow spotty afternoon and evening thunderstorms triggered by the North American monsoon over the Rockies.
During next week, the jet stream is forecast to take on a relatively straight west-to-east configuration.
Such a pattern is a relatively dry one with seasonable temperatures for the West. The pattern would not only greatly diminish monsoon-based thunderstorms, but also bring an end to any storms that erupt over the Northwest.
However, local breezy conditions may cause trouble in the pattern for active wildfires.
