textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Isolated to scattered showers today, greatest coverage northern mountain zones with minor snow accumulations above 6000 ft MSL.

- Gradual clearing this evening with temperatures around 5 degrees below normal through Wednesday.

- Dry and warmer Thursday, precipitation chances increasing Friday into the weekend.

SHORT TERM /Through Thursday Night/

Issued 207 PM MDT TUE OCT 27 2026 A weak shortwave disturbance will track across the region this afternoon and evening, generating isolated showers mainly over higher terrain and northern mountain zones. Precipitation amounts will remain light. Any lingering shower activity will diminish rapidly late this evening with the departure of the shortwave.

Skies will clear tonight behind the exiting disturbance, promoting efficient radiational cooling. Low temperatures Wednesday morning will dip into the lower to mid 30s across many lower valleys, with freezing temperatures expected in higher valleys. This will support patchy frost development Wednesday morning.

A weak upper level ridge will build overhead Wednesday into Thursday ahead of a deepening low pressure system off the Pacific Northwest coast. This pattern will bring dry conditions and a slight warming trend, with daytime high temperatures rebounding closer to seasonal normals. Another round of patchy to widespread frost is possible early Thursday morning across valley locations, as mostly clear skies and light winds foster even better radiational cooling conditions than the previous night.

By late Thursday and Thursday night, the offshore low will dig further south off the Pacific Northwest coast, shifting flow aloft to a more southerly to southwesterly direction. This will begin to advect mid and upper level moisture northeastward from the southwestern United States into the northern Great Basin. Ensemble guidance suggest sufficient moisture and weak lift could trigger isolated to scattered light showers across the central Idaho mountains late Thursday afternoon into Thursday night, while lower elevations and southeast Oregon remain mostly dry.

LONG TERM /Friday through Tuesday/

Issued 207 PM MDT TUE OCT 27 2026 Friday, a closed low off the Pacific Northwest Coast amplifies along a southward trough axis capturing a pocket of tropical moisture. As a deep Alaskan Low strengthens, it captures the closed low, trough, and tropical moisture. As they move inland, the low heads northeastward and carries the moisture and colder air inside the trough up through the forecast area. The entire synoptic process takes place from Friday through early Monday, during which precipitation chances increase and temperatures/snow levels fall. The primary cold front passes early Sunday morning in the latest ensemble means, so the weather Friday and Saturday feature modest precip chances (10-40%, higher over terrain) and snow levels around 5-7 kft MSL. Temperatures during this period hover around to just above normal for this time of year. Halloween evening (Saturday), precipitation chances increase sharply to 40-70% as temperatures and snow levels begin to dip. Sunday morning snow levels drop to 4-6 kft MSL, and by Monday they drop further to 3.5-4.5 kft MSL. At least some snowfall is likely above 5 kft MSL, and at least some chance of snow exists down to 4 kft MSL even though precipitation chances begin to decrease Sunday night, limiting how much precipitation falls when snow levels are lowest. Dry conditions will prevail through the beginning of next week. Seasonable or below normal temperatures will continue through the long-term period.

AVIATION /00Z Wednesday through Thursday/

Issued 553 PM MDT TUE OCT 27 2026

Generally VFR. Scattered showers and a stray thunderstorm this evening, bringing localized MVFR conditions in stronger showers. Widespread clearing overnight, except for LIFR/IFR conditions with patchy freezing fog and low clouds in high elevation valleys near KBNO-KMYL-KBKE. Snow levels around 5.5-6.5kft MSL. Mountains obscured in precipitation and low clouds. Surface winds: variable less than 10 kt through morning, then SW-SE 5-15 kt by early PM. Winds aloft at 10kft MSL: SW 20-30 kt.

KBOI...Scattered showers this evening, tapering off overnight with a few low clouds lingering by the foothills. Clearing skies by the early morning. Surface winds: E-SE 5-10 kt overnight then variable less than 6 kt by the late morning.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.