textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Slight warming and drying trend Tuesday and Wednesday, with light winds.

- Cold temperatures tonight will bring patchy frost to the mountain valleys.

- Another low pressure system will bring precipitation across the area Thursday and Friday.

SHORT TERM /Through Thursday Night/

Issued 205 PM MDT MON SEP 14 2026 Breezy and cool conditions will gradually diminish this evening as the upper low moves further northeast away from the area. Warm and dry conditions expected tonight under generally clear skies. Excellent radiational cooling will allow minimum temperatures to drop to around 5 degrees below seasonal averages. Patchy frost is possible in the sheltered mountain valleys by early Tuesday morning.

A weak ridge aloft will build over the region Tuesday into Wednesday, leading to a slight warming and drying trend with lighter winds. This is in response to a developing cut-off low pressure system forming over Western Oregon. Afternoon high temperatures will rebound closer to normal values for mid September. By late Wednesday, the low pressure system begins to slowly move inland. Southwest flow ahead of this system will bring increasing cloud cover and an influx of mid level moisture to eastern Oregon and southwestern Idaho, with low chances for precipitation entering western areas late Wednesday night.

LONG TERM /Friday through Tuesday/

Issued 205 PM MDT MON SEP 14 2026 The end of the work week will remain unsettled, with an upper- level low pressure system moving overhead. Precipitation chances will be highest in the west-central Idaho mountains (50-70% chance), with mentionable chances elsewhere (15-40% chance), lowest in the valleys. After this system moves out, an upper- level ridge will build into the NW U.S., bringing a clearing and warming trend back to the area. Models are split on the forecast starting next week, but a return to another unsettled pattern looks to return.

AVIATION /06Z Tuesday through Wednesday/

Issued 1208 AM MDT TUE SEP 15 2026

Generally VFR. Areas of fog/low stratus possible overnight in mtn valleys. Increasing high clouds this afternoon, mainly north and west of KTWF/KJER. Surface winds: variable under 10 kt overnight becoming E-SE 5-10 kt after Tues/17Z. Winds aloft at 10kft MSL: W-SW 10-20 kt.

KBOI...VFR. Increasing high clouds Tue/PM. Surface winds: SE 4-10 kt early Tue/AM. Becoming variable, leaning NW, under 10 kt Tue/PM.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.