Area Forecast Discussion

UPDATE

Updated aviation discussion.

KEY MESSAGES

- A strong cold front arrives this evening with gusts to 50 mph, increasing showers, and isolated thunderstorms. - Much cooler on Wednesday with widespread precipitation, isolated thunderstorms, gusty winds, and snow levels lowering to 4500 to 5500 feet.

- Precipitation totals of 1 to 2 inch in the mountains, 0.25 to 1.0 inch in the valleys.

- Snow accumulations of 10 to 20 inches on the peaks above 6000 feet especially on the northwest facing peaks.

SHORT TERM /Through Thursday Night/

Issued 242 PM MDT TUE APR 21 2026 A strong cold front moves through eastern OR this afternoon and southwest Idaho this evening. Snow levels fall to around 4000-5000 feet behind the front on Wednesday. Showers and thunderstorms form in the late afternoon in eastern OR and sweeps eastward across the area by Tuesday evening. Wind gusts up to 50 mph possible along the cold front this afternoon in eastern OR and this evening in southwest ID. The system moves overhead on Wednesday, precipitation becomes widespread for much of the day, and brings 10 to 20 inches of new snow on the peaks above 6000 feet. Total liquid equivalent precipitation of 1 to 2 inch possible over the mountains with 0.5 to 1.0 inch in the valleys. Precipitation tapers off late on Wednesday afternoon across SE Oregon, and continues over the central ID mountains into Thursday morning. Conditions dry out on Thursday afternoon with cool and breezy conditions.

LONG TERM /Friday through Tuesday/

Issued 242 PM MDT TUE APR 21 2026 A shortwave trough will bring another push of precipitation over higher terrain late Friday into Saturday, with temperatures slightly below normal through the weekend. A ridge of high pressure will build over the eastern Pacific, keeping us in cool northwesterly flow through early next week. There is some significant model disagreement in the evolution of another closed low pressure system off the Oregon Coast, which will keep precipitation chances over high terrain near the Nevada border and over the West Central and Boise Mountains in the 20-40% range Sunday through Tuesday. The ridge of high pressure will then move onshore late Tuesday, bringing a slight warming trend through the end of the week.

AVIATION /00Z Wednesday through Thursday/

Issued 635 PM MDT TUE APR 21 2026

VFR this afternoon with scattered showers. Showers becoming more widespread Tue/PM into Wed/AM with isolated thunderstorms tonight. Most likely timing of thunder from Wed/06-10z near KBKE. Conditions becoming Low IFR-MVFR in rain, MVFR-LIFR in mtn snow. Mtns becoming obscured. Snow Levels: 8+ kft MSL this afternoon, dropping to 4-6kft MSL by Wed/AM behind the front. Surface winds: SW-NW 15-30 kt with gusts to 20-40 kt behind the front. Gusts decreasing overnight before returning Wed/PM 20-35 kt. Winds aloft at 10kft MSL: S-SW 15-35 kt becoming W-NW 20-40 kt.

KBOI...VFR this evening. Rain showers increasing into Wed/AM, with MVFR conditions Wed/AM. A 30% chance of MVFR conditions persisting through Wed/PM. Surface winds: Becoming W-NW 10-20 kt with gusts to 30 kt behind a cold front. Gusts decreasing with winds SW 10-15 kt overnight.

BOI WATCHES / WARNINGS / ADVISORIES

ID...None.

OR...None.