textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Continued warm and dry through most of Wednesday.

- A chance of showers will spread northward into the area Wednesday night, then become widespread Thursday and Thursday night.

- Slight chance of thunderstorms Wednesday afternoon/evening, then a better chance Thursday afternoon and evening.

- Becoming windy late Thursday night behind a cold front.

- Much cooler Friday.

SHORT TERM /Through Thursday Night/

Issued 229 PM MDT TUE OCT 20 2026 Warm, dry weather will hold through Wednesday, although latest models have a slight chance of showers in the central Idaho Mountains Wednesday afternoon, and also near the NV/OR border Late Wednesday. Pacific upper low off the central California coast will hold quasi-stationary through mid-day Wednesday then move eastward into southern California Thursday, then northeastward into Idaho while weakening Friday. Southerly flow aloft into our CWA will moisten through Wednesday night with gradually increasing clouds, then moisten further Thursday leading to widespread rain Thursday and Thursday night, especially on the Idaho side. Latest models have more QPF than before for the Thursday/Thursday night time frame, now showing .20 to .40 inch in the Treasure and Magic Valleys, and .40 to .75 inch at higher elevations, roughly 15 percent more than the previous cycle. However, with flow aloft continuing from the south, snow levels will remain above 9000 feet, so all pcpn will be rain. Relatively less rain will fall in OR on the western flank of the upper low. That area will have .15 to 25 inch in the valleys and up to .40 inch at higher elevations and/or closer to the ID border. Latest models show enough instability for a 10-20 percent chance of thunderstorms Wednesday afternoon/evening, and a 30 percent chance of thunderstorms Thursday afternoon/evening when the upper low and surface cold front come in. Pre-frontal winds will be mainly light southeast, then shift to gusty northwest late Thursday night behind the cold front. Areas of fog will form toward Friday morning in the wetter and wind-protected northern valleys.

LONG TERM /Friday through Tuesday/

Issued 229 PM MDT TUE OCT 20 2026 Cool and wet conditions will continue as a broad low pressure system moves northeast on Friday. Breezy northwest winds with gusts ranging from 30-45 mph, widespread rain over southwest Idaho, and cool temperatures about 5-8 degrees below normal are anticipated during the day on Friday. Snow levels will lower by Friday afternoon, down to around 6000-7000 ft MSL. Higher elevation passes and ridgetops will likely only see a dusting of snow, with summits seeing close to an inch as the precipitation tapers off early Saturday. Drying conditions and near normal temperatures will return for the weekend thanks to a building ridge of high pressure over the West Coast. By late Sunday, long range forecast models begin to diverge. Some ensemble members favor a closed low pressure system moving onshore and bringing much cooler and wetter conditions by early next week, while other deterministic runs favor high pressure lingering over the Intermountain West through the middle of next week. Current forecast favors ridging and a slight warming and drying trend through Monday, with a slight chance of precipitation over the West Central Mountains.

AVIATION /00Z Wednesday through Thursday/

Issued 529 PM MDT TUE OCT 20 2026 VFR. Increasing cloud cover this evening through Wednesday, with a 10-20% chance of rain showers and around a 10% chance of thunderstorms early Wednesday morning near the NV border and the West Central ID Mountains. Mountains obscured in precipitation. Patchy smoke near prescribed burns. Surface winds: variable or E-SE 5-10 kt. Winds aloft at 10kft: SE-S 10-20 kt then S 20-30 kt after Wed/15Z.

KBOI...VFR, with increasing high clouds tonight. Vicinity showers in the early morning hours tomorrow. Surface winds: NW 4-8 kt today, then variable less than 6 kt tonight after Wed/03Z.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.