textproduct: Boise

KEY MESSAGES

- Warm and dry conditions through early Tuesday, with high temperatures 5 to 15 degrees above normal.

- Chances for precipitation increase Wednesday through Friday, with cooler temperatures by the end of the week.

SHORT TERM /Through Tuesday Night/

A closed low approaching the Pac NW coast, will turn south while still offshore on Monday. This will enhance southerly flow over the region, pushing temperatures to 10-15 degrees above normal while elevated and open terrain see wind gusts of 20 to 30 mph. Moisture increases on Tuesday, wrapping around the low as it drops off the central CA coast. With precipitable water reaching the 90th percentile, afternoon heating/instability will support a 10-15% chance of showers and thunderstorms over w-central Idaho mtns, and higher terrain along the ID/NV border Tuesday afternoon. Southerly flow could push a shower/storm into the western Magic Valley (about a 10% chance). Otherwise mild and dry conditions will continue across the area.

LONG TERM /Wednesday through Sunday/

A sharp cooldown, precipitation, thunder, and winds are all in store as successive troughs of low pressure move through the area. Wednesday through Friday, a closed low off the coast of California will rejoin the broader flow as a trough amplifies over the Pacific Northwest. A slight ridge axis over the region will allow slight warming on Wednesday as clouds increase ahead of the approaching Californian low. Temperatures that afternoon will be 10-15 degrees above normal. Wednesday evening, precipitation chances begin to increase substantially to 50-70%. Broad cloud cover will inhibit instability, but the colder atmospheric mid-layer with still warm surface temperatures allow for a 10-20% chance of thunder Wednesday evening. Clouds, precipitation, and a colder airmass moving in drop temperatures to near normal on Thursday, with precipitation chances still 50-80% and just warm enough for a 10% chance of thunder that afternoon and evening. Before precipitation tapers off Friday evening, Friday morning the cold front passes, cooling temps to about 5 degrees below normal and bringing wind gusts up to 25-35 mph out of the NW. Winds remain strong through Friday evening. Over the course of the event, rainfall accumulation is forecast at 0.05-0.3 tenths in lower elevations, and 0.25-0.5 inches for mountain valleys. Mountain summits and ridges could see 0.5-1 inch of rainfall, and 1-4 inches of snow on summits above 8000 ft MSL. Snow is unlikely on mountains until Friday morning.

Temperatures are forecast to be near normal Saturday through Sunday, with another significant upper-level trough looking to impact the area Sunday. Behind the earlier system, snow levels are lower at 6500 ft MSL. Precipitation on Sunday will fall as snow in mountain passes and the highest mountain towns if the temperature forecast holds steady. Also behind the earlier trough, mountain valley cold pools could support fog/stratus formation and allow snowfall in the valleys on Sunday.

AVIATION /18Z Sunday through Monday/

Issued 1056 AM MDT SUN OCT 18 2026 VFR under high clouds. Locally reduced visibility due to smoke/haze. Patchy fog possible again tonight. Surface winds: variable up to 12 kt. Winds aloft at 10kft MSL: SW 5-15 kt.

KBOI...VFR. Surface winds: SE 4-10 kt, becoming light and variable Sunday afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.