textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Cool with temperatures 10 to 15 degrees below normal and gusty winds on Sunday.

- Rain and snow tonight across SE Oregon with accumulations above 5000 feet.

- Patchy frost possible Monday morning in the Snake Plain mainly east of Mountain Home.

SHORT TERM /Through Tuesday Night/

Issued 254 AM MDT SUN MAY 17 2026 A cold upper level trough diving south through the Pacific Northwest. A tight surface pressure gradient and robust winds aloft will mix down to the surface, yielding widespread northwest winds of 20 to 30 mph with gusts peaking up to 50 mph. A Wind Advisory is in effect for much of the lower Snake River Plain, Owyhee County through southeast Oregon. These winds could bring areas of blowing dust that could suddenly reduce visibilities along major transit corridors.

In addition to the wind, the air mass accompanying this trough is unseasonably cold, keeping daytime highs today and Monday 10 to 15 degrees below seasonal normals. Precipitation will accompany the system today, primarily focusing light to moderate rain and snow showers over southeast Oregon and the mountains of southwest Idaho. Snow levels will drop to 3000-4500 feet MSL, allowing for light snow accumulations on higher peaks and pass levels, particularly across Harney and Malheur counties.

Winds will gradually diminish tonight as the core of the upper trough slides eastward, but the combination of clearing skies and a chilly air mass will set the stage for excellent radiational cooling. Freezing temperatures are expected across the Western Magic Valley early Monday morning, where a Freeze Warning has been issued as temperatures drop into the upper 20s to lower 30s. Elevated winds tonight are likely to keep temperatures in the mid to upper 30s across the lower Snake Plain and eastern Oregon valleys.

A gradual pattern shift begins on Monday afternoon as the trough departs and a weak transitory ridge builds inland from the Pacific. Under clear skies, temperatures on Monday will begin a slow recovery, running about 6 to 10 degrees warmer than Sunday, though still remaining cool. By Tuesday and Tuesday night, northwest flow aloft will prevail. A weak embedded shortwave grazing the northern periphery of the forecast area may trigger a few lingering light showers over the West Central Mountains, but dry conditions and a continued warming trend will be the main story for the rest of the region as temperatures climb back toward seasonal benchmarks.

LONG TERM /Wednesday through Sunday/

Issued 254 AM MDT SUN MAY 17 2026 A ridge of high pressure will build off the coast of the Pacific Northwest on Wednesday, keeping the region in mostly dry northwest flow through Thursday. A weak shortwave trough will move over Western Montana on Wednesday, bringing a slight reduction in temperatures and a 10-20% chance of showers over the West Central Mountains. The ridge of high pressure will then begin to flatten over the region, bringing a steady warming and drying trend with zonal flow over the area by Saturday. Warm daytime temperatures about 5-10 degrees above normal with generally dry conditions are expected for the weekend.

AVIATION /12Z Sunday through Monday/

Issued 601 AM MDT SUN MAY 17 2026

Generally VFR. Snow showers across SE Oregon, far SW Idaho (south of Snake Plain), and central ID through afternoon, creating IFR-LIFR in mtn snow. Mtns obscured in precipitation. Snow levels: 3000-4500ft MSL increasing to 5000-6000ft MSL by late afternoon. Scattered rain/graupel showers elsewhere. Surface winds:NW-N 15-30 kt with gusts 25-40 kt. Winds aloft at 10kft MSL: W-N 15-30 kt.

KBOI...VFR. A 20% chance of rain/graupel showers this afternoon, capable of producing erratic outflows. Surface winds: NW 5-15 kt peaking at 20-30 kt with gusts up to 30-40 kt this afternoon.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Wind Advisory from noon today to midnight MDT tonight for IDZ012-014-015-029. Freeze Warning from midnight tonight to 8 AM MDT Monday for IDZ016. OR...Wind Advisory from noon MDT /11 AM PDT/ today to midnight MDT /11 PM PDT/ tonight for ORZ061>064.