A dynamic weather pattern is unfolding across the western United States this week that will bring both temporary relief and new ignition threats to the Pacific Northwest and northern Rockies. Fire weather forecasters with the National Interagency Coordination Center are tracking a stalled upper-level low pressure system that is expected to shift eastward, bringing a mix of showers and gusty winds to the region.

This Week's Pattern

The cold, closed upper-level low that has been positioned over California is forecast to push eastward across the Columbia and Great Basins and into northern Arizona. As it moves, forecasters expect the following conditions across the Pacific Northwest:

  • Showers likely across the Pacific Northwest, providing some moisture to fire-stressed fuels
  • Gusty westerly winds across the Cascades into the Columbia Basin — a combination that can fan any existing fires
  • Below-normal temperatures across much of Oregon and western Washington
  • Thunderstorm potential over the mountains of Idaho and most of Montana — a significant concern for dry lightning ignitions

Dry Lightning Threat

Of particular concern to fire managers is the threat of dry or mixed thunderstorms over Idaho and Montana. The NIFC weather forecast notes there is "higher potential for thunderstorms further north and east across the mountains of Idaho and most of Montana." These storms are expected to produce a mix of wet and dry lightning strikes — meaning some may produce rainfall that reaches the ground, while others deliver only lightning.

Dry lightning events have historically been responsible for some of the most damaging multi-fire starts in the Pacific Northwest. A single thunderstorm cell can ignite dozens of fires simultaneously, overwhelming initial attack resources before crews can respond to each ignition.

Critical Fire Weather Elsewhere

While conditions are somewhat moderated in the Pacific Northwest this week, critical fire weather conditions are forecast for portions of the Four Corners states, with gusty winds of 40-45 mph and relative humidity levels between 7-20%. Dry thunderstorm potential also exists across eastern Nevada, southern Utah, and northwest Arizona.

Looking Ahead: Summer Heat Building

After this week's cooler pattern, temperatures are expected to rebound across the Pacific Northwest. Forecasters warn that the Northwest east of the Cascades remains at elevated risk through June, with conditions likely to worsen in July as high pressure builds and moisture becomes increasingly scarce across Idaho and the northern Rockies.

Residents and outdoor recreationists in fire-prone areas should check current Red Flag Warning and Fire Weather Watch status through the National Weather Service offices in Boise (weather.gov/boi), Spokane (weather.gov/otx), and Pendleton (weather.gov/pdt) before heading into backcountry areas or engaging in activities that could spark a fire.