textproduct: Boise

KEY MESSAGES

- Warm and dry Today with light winds.

- A chance of showers and thunderstorms Friday night through Saturday. Storms Friday night and Saturday morning could produce strong outflow winds, but storms later Saturday may bring heavy rain, especially over higher terrain in Idaho.

SHORT TERM /Through Saturday Night/

An upper level trough shifting eastward across the Pacific Northwest today will tighten pressure gradients across southeast Oregon and southwest Idaho. This will result in breezy west to northwest winds of 15 to 25 mph, with local gusts up to 35 mph, especially across the Western Snake River Plain and higher terrain. Combined with minimum relative humidity values dropping into the 10 to 15 percent range for lower elevations, elevated fire weather conditions are expected again today prompting the Red Flag Warning. Temperatures will be about 5 to 7 degrees cooler today from yesterday.

Winds will decouple tonight as a weak transitory ridge builds into the region. Thursday looks to be a quieter, warmer day under the influence of this ridge. Temperatures will be in the upper 80s to low 90s across the lower valleys Thursday. Relative humidity values will remain quite low on Thursday, but light terrain driven winds will limit the overall fire weather threat compared to today.

More active weather is expected on Friday with an incoming low pressure system moving onshore over northern California. This system will bring an influx of mid level moisture and instability into southeast Oregon and southwest Idaho. Model guidance continues to signal a distinct threat for thunderstorm development starting Friday afternoon and evening. Given initial low levels remaining relatively dry, these storms will carry a risk of dry lightning and strong, erratic outflow winds, increasing fire ignition potential. Wind gusts of 50 to 60 mph with blowing dust is possible (10% chance) especially across southeast Oregon. The ridge will reach peak amplitude over southern Idaho Friday in response to the approaching trough bringing temperatures back into the mid 90s across the lower valleys.

LONG TERM /Sunday through Thursday/

As the core of the low moves closer on Saturday, moisture profiles deepen significantly, bringing a mix of wet and dry thunderstorms and increasing the threat for heavy rain and flash flooding on burn scars. The best chance for thunderstorms (30 to 60%) looks to be across the higher terrain of southwest Idaho. With precipitable water approaching the 80th to 90th percentile, the strongest storms could produce heavy rain in addition to small hail and gusty winds. Burn scars, like the Wapiti Burn Scar, will need to be monitored for flash flood potential.

Cooler air accompanying the system will knock temperatures down by Sunday, returning highs closer to seasonal normals. High pressure builds back over the region early next week, leading to a return of dry conditions and a steady warming trend through Wednesday. The upper level flow remains active and thus the warming looks to be short lived.

AVIATION /06Z Thursday through Friday/

Issued 1202 AM MDT THU JUN 18 2026 VFR. Surface winds: W-NW 5-15 kt tonight. Winds aloft at 10kft MSL: NW 15-25 kt.

KBOI...VFR. Surface winds: light and variable overnight, becoming NW 7-12 kt after 18/18z.