textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Showers will become widespread this afternoon through Friday morning, along with isolated to scattered chances for thunderstorms.

- Thunderstorms this afternoon into evening will be capable of isolated severe wind gusts, localized flooding, and small hail in Southwest Idaho.

- Windy conditions will develop late tonight and tomorrow behind a cold front, with much cooler conditions Friday and Saturday.

SHORT TERM /Through Saturday Night/

Issued 413 AM MDT THU OCT 22 2026 The upper-level low is moving into central California this morning. Isolated light showers are already ongoing, moving north through the area. Coverage is expected to increase further in SE Oregon this morning, then becoming widespread in both SE Oregon and SW Idaho this afternoon. As the low pressure system moves into Nevada through the day, chances for thunderstorms increase from isolated to scattered. The chance for scattered thunderstorms will be greatest in SW Idaho, where favorable convective parameters will align. The primary threat from these thunderstorms will be outflow wind gusts up to 50 mph, with a secondary threat of localized flooding, and a tertiary threat of small hail. The time frame of this threat will begin this afternoon and taper off by evening. Winds will gradually increase from the southeast through the day, especially in and south of the Snake Basin. Winds will shift out of the west/northwest Thursday night behind the cold front, with sustained 15 to 25 mph and gusts 30 to 40 mph Friday.

QPF totals as this event begins today (through Friday night) are: 1.00 to 1.25 inches in the higher terrain of SW Idaho, 0.70 to 1.00 inches in central and southern Harney county, 0.60 to 0.80 inches in mountain valleys, 0.40 to 0.75 inches in the Snake Basin, and 0.40 to 0.70 inches in Baker, Malheur, and the rest of Harney counties. Higher totals will be seen where thunderstorm cores pass over. A Flash Flood Watch is in effect for the Wapiti and Crooked Burn Scars beginning Thursday night through Friday morning. Shower and thunderstorm chances will gradually end from west-to-east across the area Friday behind the cold front. Snow levels behind the front will drop to 5000-6500 ft MSL, lowest in SE Oregon, while precipitation is clearing out Friday morning/afternoon. The highest peaks could see a few inches, however a dusting is what most elevations near/above 6000 ft MSL will see.

Late Friday afternoon / evening, flow aloft will switch out of the northwest as the last remnants of the low pressure system move east of the area. Our CWA will then dry out and become significantly colder, with low temps Saturday morning in the teens and 20s in the mountains and lower to mid 30s in the valleys, while high temps stay mostly in the upper 40s and 50s. As winds die down and clouds clear out, areas of fog will develop Friday and Saturday nights.

LONG TERM /Sunday through Thursday/

Issued 413 AM MDT THU OCT 22 2026 Short-lived upper-level ridging will build in Sunday as the area is between a closed low in the Four Corners and another system moving into the Pacific NW. This will enable dry conditions and a slight warming trend through Monday, causing temperatures to climb to about 5 degrees above normal Sunday and Monday. Cooler and wetter conditions are expected to return during the mid week as the upper-level trough moves further inland and overhead. Lingering forecast uncertainty exists for the timing and track of this low pressure system, with disagreement present in ensemble solutions and between deterministic models. Current forecast shows this cut off low bringing much cooler, below normal temperatures and 20-40% chances of precipitation over the higher terrain of eastern Oregon and west-central Idaho. Snow levels will likely range from 5500-6500 ft MSL, depending on the track of the low pressure, with light mountain snow accumulation.

AVIATION /12Z Thursday through Friday/

Issued 623 AM MDT THU OCT 22 2026

Scattered rain showers and isolated t-storms moving from south to north this morning, becoming widespread in the afternoon. Gusty outflow winds up to 50 kt, small hail, and heavy rainfall will be possible in stronger t-storms, mainly in southwest ID. Mountains obscured in rain and lowering ceilings. Surface winds: S-E 5-12 kt with gusts 20-25 kt east of KMUO through morning. Cold front tonight shifting winds out of the W-NW 15-25 kt with gusts 30-40 kt. Winds aloft at 10kft: S 15-30 kt.

KBOI...VFR. Widespread rain showers and isolated embedded thunderstorms this afternoon/evening. Heavy rain, small hail, and gusty outflow winds near 40 kt possible in stronger storms. Surface winds: variable under 10 kt through morning, then SE 8-15 kt with gusts 20-25 kt in the afternoon.

Weekend Outlook...Rain/snow mix will be lingering across SW Idaho Friday until evening. Areas of MVFR-IFR will remain as ceilings remain low and precipitation causes mountain obscuration. Snow levels behind the front will drop to 5000-6500 ft MSL, lowest in SE Oregon, while precipitation is clearing out Friday morning/afternoon. Areas of fog will form Saturday and Sunday mornings, especially in sheltered mountain valleys. Otherwise clear skies and cooler conditions can be expected Saturday and Sunday. Surface winds: W-NW 10-20 kt with gusts 30-40 kt Friday, light and variable under 12 kts Saturday and Sunday.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Flash Flood Watch from 6 PM MDT this evening through Friday morning for IDZ013. OR...None.