textproduct: Boise

UPDATE

Updated aviation discussion.

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/

Issued 400 AM MDT SUN OCT 18 2026 Temperatures today will be a few degrees cooler with lighter winds in the wake of a passing upper-level trough moving along the international border. Southwesterly flow aloft will gradually increase in strength today and early Monday as the Gulf of Alaska low moves towards and then along the Pacific NW coast. Model guidance remains consistent in keeping the closed low offshore as it passes our latitude on its way south. Flow aloft will shift to be out of the south during the day Monday, helping increase temperatures back to 10-15 degrees above normal. The flow aloft will also result in gusty afternoon winds across open/elevated terrain, which will overlap with low afternoon relative humidity across the area (particularly southern Harney and Malheur counties). As the low moves further south Tuesday, the pressure gradient will decrease, decreasing wind speeds from Monday. Continued southerly flow aloft will bring increasing mid-level moisture back into the region, increasing cloud cover and introducing slight chances for precipitation. Models are showing marginally favorable convective parameters over the w-central Idaho and eastern Boise Mtns, which are covered by a 20-30% chance of showers for Tuesday afternoon. Temperatures will slightly cool from Monday, back to near 10 degrees above normal.

LONG TERM /Wednesday through Sunday/

Issued 400 AM MDT SUN OCT 18 2026 The upper-level low pressure system will slowly move inland into the Great Basin Wednesday and Thursday. At the same time, another upper-level trough will approach the BC, Canada coast. Ensembles have the closed low in the Great Basin rejoining the flow and moving east of the area Friday and Saturday. Most areas see a chance of precipitation during this period, though the track of the low continues to favor SW Idaho zones with the greatest coverage and amounts. The heaviest rainfall totals remain focused over w-central Idaho, with widespread 0.25-0.50 inch amounts and locally up to 0.75 inches for Thur/Fri. Thunderstorm chances also accompany the precipitation chances, with the greatest coverage and percentage chances happening on Thursday. Snow levels will drop from 9-10kft MSL Wed/Thur to 6-8kft MSL on Friday as the wrap around precipitation ends. Additionally, late Thursday into Friday, a significant cold front is expected to move through the area. Winds through the western Snake Plain are expected to be 20-30 mph Friday afternoon as that moves through the area. Temperatures are forecast to be near- or just below-normal Friday through Sunday, with another significant upper-level trough looking to impact the area Sunday.

AVIATION /12Z Sunday through Monday/

Issued 510 AM MDT SUN OCT 18 2026

VFR under high clouds. Locally reduced visibility due to smoke/haze. Patchy fog developing near KBNO and KBKE Sun/AM. Surface winds: variable up to 12 kt. Winds aloft at 10kft MSL: SW 10-25 kt.

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

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.