textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- High temperatures 5 to 15 degrees above normal through Wednesday.

- Shower and thunderstorm chances return starting Tuesday afternoon, and greatly increase Wednesday through Friday.

- Cooler temperatures expected by the end of the week.

SHORT TERM /Through Wednesday Night/

Issued 354 AM MDT MON OCT 19 2026 The upper-level low that is expected to be the weather maker for a few days is moving into the Pacific NW coast this morning. Flow aloft will continue to increase out of the southwest as it moves nearly due south today, staying just off the California coast. Southwesterly flow aloft will give way to southerly flow aloft tonight, which will continue to keep temperatures 10-15 degrees above normal, with elevated and open terrain seeing wind gusts of 20 to 30 mph. The southerly flow aloft will continue Tuesday and Wednesday, with widespread precipitable water values forecast to reach the 90th percentile by Wednesday. Afternoon heating/instability Tuesday will support a 10-15% chance of showers and thunderstorms over the w-central Idaho mountains, the western Magic Valley, and the higher terrain along the ID/NV border. Convective parameters will largely be limited by CAPE values as the environment becomes more favorable through day Tuesday into Wednesday. If a stray thunderstorm does overcome the odds Tuesday afternoon, the mostly dry lower levels of the atmosphere will support the primary threat of outflow wind gusts 30-40 mph. Minimal accumulations outside of thunderstorm cores are expected with any showers / thunderstorms.

Shower and thunderstorm activity is expected to increase in coverage overnight Tuesday into Wednesday. The primary threat will become localized heavy rainfall underneath thunderstorm cores as PWATs increase. Precipitation chances will continue through the day Wednesday, and sharply increase overnight Wednesday into Thursday. The low pressure system is expected to slowly move onshore late Wednesday, rejoining the flow aloft as another system moves into the Pacific NW.

LONG TERM /Thursday through Monday/

Issued 354 AM MDT MON OCT 19 2026 The low pressure system will move NE over the area through the day Thursday into Friday. Shower and thunderstorm chances will be greatest during this time, especially as it moves overhead. Broad cloud cover will limit instability, but the colder atmospheric mid-levels (with still warm surface temperatures) will enable a 10-20% chance of thunderstorms. Clouds and precipitation will keep temperatures near normal on Thursday, with widespread precipitation chances 50-90%. Precipitation chances will gradually clear west-to-east across the area Friday as a cold front moves through. This front will cool temperatures to 5-10 degrees below normal Friday and bring wind gusts up of 30-40 mph out of the NW. The highest gusts will be seen along the ridgetops of SE Oregon and through western Snake Plain. Winds will remain strong through Friday evening. Precipitation totals have been increasing over the past few model runs. Over the course of the event, rainfall accumulation is forecast at 0.1-0.3 inches in lower elevations, and 0.25-0.75 inches for mountain valleys. Mountain summits and ridges could see 0.5-1 inches of rainfall, and 1-4 inches of snow on summits above 8000 ft MSL. Snow is unlikely on mountains until Friday morning when the cold front drops snow levels from near 9000 ft MSL to 4500-6000 ft MSL (lowest in SE Oregon).

Temperatures are forecast to be near normal Saturday through Sunday, with another significant upper-level trough looking to impact the area Sunday into Monday. Behind the earlier system, snow levels will remain around 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 and Monday.

AVIATION /18Z Monday through Tuesday/

Issued 1017 AM MDT MON OCT 19 2026

VFR under high clouds. Locally reduced visibility due to smoke from prescribed fires. Surface winds: S-E 5-15 kt, with localized gusts to around 20 kt this afternoon in SE Oregon. Generally becoming light and variable overnight. Winds aloft at 10kft MSL: S-SW 10-25 kt.

KBOI...VFR. Surface winds: SE 6-12 kt with afternoon gusts 15-20 kt, becoming light and variable overnight.

BOI WATCHES/WARNINGS/ADVISORIES

ID...None.

OR...None.