Fire weather forecasters are tracking a high-risk pattern across much of the western United States this week, with elevated to critical conditions expected to persist across the Southwest, Great Basin, California, and portions of the Rocky Mountains. The pattern comes as fuel moisture levels drop to their lowest levels of the year ahead of the peak summer fire season.

The Fire Weather Setup

A strong, persistent high-pressure ridge over the Interior West is responsible for the extreme heat and low relative humidity affecting the region. Key conditions include:

  • Relative humidity: 5–15% across the Southwest, Great Basin, and Rocky Mountain areas — critically low values that allow fires to spread rapidly and respond dramatically to wind.
  • Winds: Variable 10–15 mph with gusts reaching 15–35 mph, with the highest values across west-facing slopes and the central Great Plains.
  • Temperature: Above 100°F expected across central California valleys, the Las Vegas corridor, and southern portions of the Southwest.

Dry Lightning Threat

In addition to human-caused ignitions, a dry thunderstorm threat is developing across portions of Arizona. More widespread thunderstorms are expected across eastern New Mexico and southeastern Colorado — areas where storms can produce lightning strikes with little or no accompanying rainfall to reduce fire starts.

In the northern Rockies, including northern Idaho and Montana, scattered thunderstorms are moving eastward accompanied by gusty and shifting winds. These storms will bring higher relative humidity to some areas but gusty outflow winds can create rapid fire spread on existing fires or new starts.

What This Means for the Pacific Northwest

Directly in the Pacific Northwest, conditions entering this week are not yet at critical levels in most western Oregon and Washington valleys, where marine influence moderates temperatures. However, east of the Cascades — in central and eastern Oregon, central and eastern Washington, and across Idaho — conditions are rapidly deteriorating as the heat dome expands northward.

The Highway 730/Twin Sisters Fire, which ignited overnight in Walla Walla County and crossed into Oregon Sunday morning, is an example of how quickly conditions can turn dangerous in the Columbia Basin and eastern Oregon/Washington dryland areas, where fine fuels of cured grass dry out extremely early in the season.

Red Flag Warning Indicators

The National Weather Service issues Red Flag Warnings when a combination of low relative humidity (typically below 15–25%), sustained winds above 15 mph, and critically low fuel moisture create conditions where fires can start easily, spread rapidly, and be difficult to control. Multiple Red Flag Warnings and heat advisories are in effect across the country this week.

Residents in eastern Oregon, eastern Washington, and Idaho should treat this period as high alert — avoid any activities that could cause a spark, including mowing dry grass, grinding metal, operating off-road vehicles in dry vegetation, and any open burning.

Looking Ahead

Both weather models and fuel moisture outlooks predict continued or increasing fire danger across multiple geographic areas in the coming weeks. NIFC forecasters note that as the summer progresses, large areas of the West are expected to see above-normal fire potential, particularly across the northern Rockies, Great Basin, and Pacific Northwest east of the Cascades.