textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Dry through Thursday, with near normal temperatures.

- Precipitation chances increasing across higher terrain Friday afternoon. Becoming widespread Saturday afternoon into Sunday.

- A drying and warming trend will set in Monday, through at least midweek.

SHORT TERM /Through Friday Night/

Issued 205 PM MDT WED OCT 28 2026 Following the departing shortwave, skies have continued to clear across southeast Oregon and southwest Idaho. With light winds and mostly clear skies tonight, radiational cooling will allow temperatures to drop into the upper 20s to mid 30s across many lower valleys,resulting in areas of patchy frost late tonight into Thursday morning.

A brief warming and drying trend will take hold on Thursday as weak transient ridging moves overhead ahead of an approaching upper level developing off the Pacific Northwest coast. Afternoon temperatures on Thursday will rebound to near or slightly above seasonal, with quiet weather prevailing across the region through early Thursday evening.

Late Thursday night into early Friday, southwesterly flow aloft will strengthen over the Great Basin and northern Intermountain West.A weak shortwave trough embedded in this southwesterly flow will lift northeastward across the area. While moisture availability remains somewhat limited, sufficient moisture will advect northward to south-central Idaho to support isolated to scattered showers late Thursday night through Friday.

Snow levels will hover around 6000 to 7000 feet during morning increasing to 8000 feet by afternoon. This will primarily yield light rain in the lower valleys, but a dusting to a few inches of snow possible across the higher peaks and mountain passes, including Banner Summit. For the remainder of southwest Idaho and southeast Oregon, Friday will feature passing cloud cover and slightly cooler afternoon temperatures, with dry conditions continuing through Friday night before the main Pacific trough approaches for the weekend.

LONG TERM /Saturday through Wednesday/

Issued 205 PM MDT WED OCT 28 2026 Saturday, a closed low with an elongated southern trough begins to swing up and north of the forecast area, bringing the trough, a cold front, and wetter conditions. This trough will have a good pull of Pacific moisture ahead of it, with precipitable water values increasing to around the 90th percentile in southwest Idaho. The anomalous atmospheric moisture will be coincident with largescale forcing, leading to increasing precipitation chances through the day Saturday, reaching 50-80% Saturday evening and night as a cold front crosses the area. Hopefully your plan is to dress up as Mary Poppins for Halloween, just in case. Snow levels will initially begin at 6-8 kft MSL, lowering to 4.5-6.5 kft MSL by Sunday afternoon. Lowering snow levels occur alongside decreasing precipitation chances as conditions dry out behind the front. Overall, the bulk of any snow accumulation will remain above 6.5 kft MSL, with generally 2-5 inches of accumulation (Locally up to 7 on the highest peaks). The lowering snow levels could allow for snow or wintry mix as low as 4.5 kft Sunday, although little accumulation is anticipated as precipitation tapers off behind the departing system. Ridging will build in behind the departing system, allowing for dry conditions Monday afternoon through at least mid-week. Temperatures will be seasonable or below normal throughout the period.

AVIATION /06Z Thursday through Friday/

Issued 1123 PM MDT WED OCT 28 2026

Generally VFR. Localized LIFR/IFR conditions with patchy freezing fog and low stratus in high elevation valleys in southeast Oregon. Mountains obscured in fog and low stratus. Surface winds: variable less than 10 kt through morning, then NE-SE 5-15 kt by early PM. Winds aloft at 10kft MSL: SW-S 20-30 kt.

KBOI...VFR. Increasing high cloud cover through the day. Surface winds: E-SE 5-10 kt, with gusts to 20 kt by late morning.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.