Boise, Idaho

• Isolated to scattered showers and thundestorms through this evening.
• Widespread rain and high elevation snow late tonight into Sunday.
• Cooler with gusty winds Sunday, and especially Sunday night, then drying and warming Monday through Wednesday. Slight chance of precipitation late week.

The primary forecast challenge in the near term centers on convective potential late this afternoon and evening. Water vapor imagery shows a vigorous upper level trough digging into the Pacific Northwest, pushing increasing mid-level moisture into southeast Oregon and southwest Idaho. Modest surface heating combined with synoptic forcing supported by the nose of the subtropical jet will foster scattered showers and isolated thunderstorms late this afternoon through mid-evening. Weak shear profiles suggest pulse-type activity, though gusty erratic outflow winds and brief heavy rain will be possible with any stronger cores. High-res guidance remains in good agreement with a line of showers and thunderstorms tracking southwest to northeast through the Snake River Plain between 6 PM and 8 PM MDT tonight, right during peak trick-or-treating hours. Bottom line, be prepared for brief showers and isolated thunderstorms this evening.

Showers will become more widespread late tonight as precipitable water values increase into the 75th percentile. Precipitation will shift mainly into southwest Idaho early Sunday and persist until late Sunday afternoon as the cold front finally tracks through. Snow levels remain high (between 7000 and 8000 feet MSL) while the area sits in the warm sector through much of the event. Expected rainfall totals through Sunday are around 0.25 inches in the Treasure Valley, close to 0.50 inches in the Western Magic Valley, and around 0.75 inches across the south-central Idaho mountains. Generally less than 0.20 inches is expected across much of southeast Oregon.

As the cold front pushes through the region Sunday evening, strong cold air advection and a tightening surface pressure gradient will generate windy conditions across the forecast area. The strongest winds will align along the Snake River Plain from Mountain Home eastward through the Western Magic Valley, where westerly gusts of 40 to 45 mph are expected from late Sunday evening through Monday morning.

Winds will gradually diminish by Monday afternoon as the surface gradient relaxes and high pressure begins to build in from the west. Cool, dry, and settled conditions will prevail region-wide Monday night under clear to partly cloudy skies with near to slightly below normal overnight lows. Given the cloudy conditions tonight and breezy surface winds Monday morning, fog isn`t likely to become a widespread issue despite wetting rains tonight through Sunday.

The upper-level ridge will be breaking down Tuesday as an upper- level shortwave trough moves inland and overhead through Wednesday. The extent to how fast it moves through the area and east is disputed across the long range models, but breezy conditions and cloudy skies are the expected impacts. By late Wednesday the next pattern change is quickly moving in, with successive additional troughs expected late week. Precipitation chances area wide increase to 10-30% late Wednesday night and Thursday, and further rising to 20-50% on Friday. These systems will be weak, keeping similar, near- normal temperatures from day to day. A ridge of high pressure is likely to build overhead on Saturday with a return to dry conditions.

Issued 1228 PM MDT SAT OCT 31 2026

Mainly VFR with isolated to scattered showers through the afternoon. Isolated thunderstorms across S Idaho and far SE Oregon late this afternoon through the evening. Showers becoming widespread tonight. Most sites MVFR-IFR overnight from low ceilings. VFR-MVFR in rain showers, IFR-LIFR in mountain snow. Mountains obscured in precipitation. Snow levels 6500-8000 ft MSL. Surface winds: SE- SW 5-10 kt with gusts up to 30 kt from thunderstorm outflow. Winds aloft at 10kft MSL: S-SW 10-20 kt.

KBOI...VFR through the afternoon. Isolated showers through mid afternoon, becoming widespread tonight. Isolated thunderstorms possible (10-15% chance) late afternoon/evening. MVFR ceilings and visibility during heavier showers this evening, prevailing MVFR overnight. IFR conditions expected to develop overnight, with the highest chances being after 01/08z. Surface winds: variable to SE 4-8 kt, becoming W-NW 4-8 kt overnight.

Sunday Outlook...Precipitation gradually tapering off from W-E. VFR-MVFR in rain showers, IFR-LIFR in mountain snow. Mountains obscured in precipitation. Area wide patchy fog expected through morning. Snow levels lowering to 5500-6500 ft MSL. Surface winds: W-NW 10-20 kt with gusts 20-35 kt behind a cold front, strongest east of KBOI through the western Magic Valley.

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