textproduct: Boise

KEY MESSAGES

- Isolated to scattered showers today, greatest coverage northern mountain zones. 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/

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/

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 /18Z Tuesday through Wednesday/

Issued 1123 AM MDT TUE OCT 27 2026 Mountains obscured and scattered rain and mtn snow showers are expected through the afternoon. Low VFR to IFR in showers. Another round of showers arrives overnight in northern mountains near KMYL. Snow levels 5000-6000ft MSL drop to 4000-5000ft MSL tonight. Surface winds: Variable 5-15 kt. Winds aloft at 10kft MSL: W 10-25 kt.

KBOI...Generally VFR. Isolated rain/graupel showers will develop this afternoon. They will stay over the foothills with a low chance of impacting the airport. Surface winds: SE 3-8 kt this morning, shifting to NW 3-8 kt this afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.