Air quality may worsen as warm, dry pattern holds west of the Rockies
A persistent weather pattern will bring sunny, dry and unusually warm conditions to much of the western U.S. and southwestern Canada, with springlike temperatures, foggy areas and limited storm activity this week.
Dozens of bald eagles were seen gathering on a snowy mountain near New Aiyansh, British Columbia, surprising viewers with an uncommon display of the typically solitary birds.
Dry, warm weather will be widespread across much of the western United States and southwestern Canada this week, but stagnant air could trap pollution in some areas and lead to stubborn fog.
When the jet stream bulges far north, as it will into early week, storms are forced to take a long detour. This dry pattern leads to light winds and a mostly clear sky across the region.
Where the sky stays clear at night and it is sunny during the day, there are typically large temperature swings, with a chill setting in quickly after sunset, followed by rapid warming around midday.
This type of weather setup often leads to temperatures well above historical averages. In many areas, including Seattle, San Francisco and Salt Lake City, high temperatures will run 5-10 degrees above average for mid-January. For reference, average daily highs are in the upper 40s in Seattle, the upper 50s in San Francisco and the upper 30s in Salt Lake City.
In some locations, such as Los Angeles, temperatures will reach the 70s, or 5-10 degrees above historical averages. In Phoenix, highs will be mainly in the upper 70s to near 80 through the middle of the week. In Las Vegas, highs will range from the mid-60s to near 70.
The same weather setup responsible for the dry, warm conditions and light winds could also cause fog to form in valleys and linger well into midday. In some areas, including much of California’s Central Valley, dense Tule fog may linger for days. The Central Valley of California has already had multiple stretches of Tule fog earlier this winter. One from late November into late December lasted three to four weeks.
When fog is slow to dissipate or fails to clear, temperatures may rise little or not at all during the day, and conditions could remain stuck, repeating this setup for several days.
By the middle to latter part of this week, the jet stream may shift south again, allowing storms to move in, though they might not be as strong as those in December. The stormy pattern change will help disperse the fog and rid the region of some of the stagnant air.
This image was captured on Monday, Jan. 19 2026, during the midday hours. Low clouds and fog are visible over the interior western United States (center). Multi-layered clouds were visible off the California coast (left). (AccuWeather Enhanced RealVue™ Satellite)
Until then, stagnant air for several days may allow pollutants to build up and cause poor air quality, posing a health risk for sensitive individuals and those with respiratory conditions.
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According to AccuWeather’s long-range team, conditions across much of the western United States in February may resemble those seen in mid-January.
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