textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Gusty winds today ahead of a Pacific cold front, resulting in critical fire weather conditions in southeastern Oregon.

- Scattered showers/thunderstorms this afternoon and evening with outflow gusts as strong as 55 mph and blowing dust, mainly over south-central Idaho.

- Much cooler Tuesday with gusty west/northwest winds and chance of showers and thunderstorms. Better chance of showers and thunderstorms Wednesday through Friday and continued cool.

SHORT TERM /Through Wednesday Night/

Issued 314 AM MDT MON MAY 25 2026 Today will be the warmest day with high temps 10-15 degrees above normal. A strong Pacific cold front will pass through eastern Oregon overnight and into western Idaho Tuesday morning. The supporting deep, cold upper low will track southward down the WA and OR coasts today and tonight, inland into SW Oregon Tuesday morning, then going as far south as central Calif Wednesday. The generally southward track of this low will limit how far east the cold front moves across Idaho, but models carry it past TWF Tuesday although weakening there. Eastern OR will cool 25 to 30 degrees from today but south-central Idaho will cool only about 15 degrees. However, before the cold front comes in, thunderstorms (15 to 30 percent areal coverage) will develop in south-central Idaho this afternoon, then shift northward into central ID this evening. Thunderstorms may produce outflow wind gusts to 50 mph and blowing dust, but rain amounts are forecast less than .10 inch even in the wettest storms. The cold front itself will have a better organized rain-band when it passes through eastern OR overnight before weakening in western ID Tuesday. However, Tuesday evening looks wetter with more numerous showers and 50-80 percent PoP (greater in ID than OR) as moisture surges northward into our CWA. By Wednesday morning that moist surge will be in central ID, pivoting westward back into OR during the day Wednesday via the upper flow around the main upper low. By Wednesday afternoon it will be in southeast OR and becoming even wetter as more moisture enters through NV around the upper low. Altogether, rainfall through Wednesday night should total .25 to .50 inch, heaviest in the Idaho central mountains and in southern Harney and Malheur Counties. The Snake Basin will have only .05 to .15 inch, least in south- central ID, but south-central ID can expect the strongest thunderstorm outflow winds (up to 50 mph).

LONG TERM /Thursday through Monday/

Issued 314 AM MDT MON MAY 25 2026 The stretch of active weather will continue throughout much of the long-term period. The upper-level low will remain over the Great Basin throughout the coming week. As we get into Friday/Saturday, a trough digging down the coast of British Columbia will send the filling Great Basin low northward over our area as a shortwave trough. The best chance for wetting rain will come over that same time frame.

With cold air aloft, sufficient mid-level moisture, and afternoon destabilization, the threat of thunderstorms will persist through the end of the week. While each afternoon will be the preferred timing for thunderstorms (especially if we get daytime clearing in cloud cover), nocturnal storms can't be ruled out. Temperatures through the end of the week will be near (leaning below) normal, with breezy winds each afternoon. Ensemble guidance has the low out of our area come early next week with building ridge centered over the High Plains, this will support a warming trend to start next week.

AVIATION /12Z Monday through Tuesday/

Issued 518 AM MDT MON MAY 25 2026

Generally VFR. Scattered thunderstorms over SW Idaho and far NE Oregon Mon/PM. Thunderstorms capable of 30-50 kt outflows and blowing dust. Showers increasing across E Oregon early Tue/AM, with ceilings lowering to MVFR near KBKE/KBNO. Surface winds outside of storms: Variable up to 12 kt this morning. Then SE- SW 10-20 kt with afternoon gusts to 15-35 kt. A cold front will switch winds to be W-NW 10-25 kt with gusts to 20-40 kt, strongest near KBKE/KONO. Winds aloft at 10kft MSL: S-SW 10-25 kt.

KBOI...VFR. A 30% chance of thunderstorms affecting the terminal between Mon/20z-Tue/00z. Thunderstorms will be capable of outflows to 30-50 kt, lightning, and areas of blowing dust. Surface winds outside of storms: SE-S 8-12 kt. Becoming NW 10-15 kt tonight following a cold front.

FIRE WEATHER

High temperatures well above seasonal normals, minimum RH 10-15%, and gusty winds 30-45 mph prompted issuance of a Fire Weather Watch in Southeast Oregon for this afternoon and evening. A Pacific cold front, expected late tonight, will bring gusty pre-frontal southwest winds within the already warm and dry environment. Scattered thunderstorms in southwest Idaho this afternoon and evening will bring lightning and outflow wind gusts as strong as 55 mph. Fire danger will increase, with wildfires and prescribed fires already present in the Western Twin Falls BLM, Boise BLM/NF and Payette NF. Morning RH will be substantially higher Wednesday through next Sunday, and there will be a 30-40% chance of wetting rain each day as the main low pressure system aloft remains right over the district.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...Fire Weather Watch from 2 PM PDT this afternoon through this evening for ORZ670-672.