textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Frost Advisory for the western Magic Valley Tuesday morning.

- Lighter winds and drier with a gradual warming trend through Wednesday.

- Generally dry with above normal temperatures through the weekend. Potential pattern change early next week.

SHORT TERM /Through Wednesday Night/

Issued 242 PM MDT MON MAY 18 2026 The afternoon/evening showers and isolated thunderstorms will diminish with sunset, as will the gusty winds. Lighter winds and clear skies overnight allow for possible frost in the western Magic Valley Tuesday morning. There is a spread in forecast low temperatures with a range of 33 to 38 in the Gooding/Jerome/Twin area so coverage could be patchy. Have opted with a Frost Advisory to highlight the potential. Building heights behind the exiting trough will bring a gradual warming trend with high temperatures close to normal by Wednesday. Mountains will see an afternoon cumulus field from daytime instability. Can't rule out a mtn top shower over w-central Idaho mtns (east of McCall- Lowman-Atlanta line) each afternoon, but it would be light with heavier development further north and east. An approaching trough will increase precipitation chances across these areas Wednesday night. Winds settle down Tue/Wed staying below 15 mph for most sites.

LONG TERM /Thursday through Monday/

Issued 242 PM MDT MON MAY 18 2026 Come Thursday, a shortwave embedded in the northwesterly flow aloft will begin to dig into southeastern Idaho. While the better forcing associated with this shortwave will be east of our area, height falls aloft will support isolated showers developing over higher terrain in the West Central and Boise Mountain zones. Following this trough, dry northwest flow will return with higher pressure building in aloft over the Pacific; as a result, a warming trend will set in through the weekend, with temperatures 5-10 degrees above normal.

Come Sunday, flow aloft will become more zonal as a Gulf of Alaska low deepens. The exact track of this low is a bit uncertain this far out; however, the grand ensemble shows the indication of troughing moving across our area come early next week (deterministic guidance varies on strength and track). Despite the uncertainty, the signal is there for a pattern change early next week, this will lead to increasing precipitation chances and cooler temperatures (although still leaning above normal) come Monday. With the main jet stream above our area throughout the long-term period, breezy conditions will stick around each afternoon. The windiest conditions of the period will likely come early next week as the low makes it's way into our area.

AVIATION /00Z Tuesday through Wednesday/

Issued 600 PM MDT MON MAY 18 2026

VFR. Virga/isolated showers over higher terrain before sunset. Surface winds: W-N 5-15 kt with gusts to 20-25 kt tapering off around sunset, then variable 5-10 kt overnight. Winds aloft at 10kft MSL: transitioning from NW to W, 5-15 kt.

KBOI...VFR. Virga/isolated showers over foothills before sunset. Surface winds: NW 10-18 kt with gusts around 25 kt, decreasing to W-NW 5-10 kt around sunset. Becoming light and variable by early AM.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Frost Advisory from 4 AM to 8 AM MDT Tuesday for IDZ016. OR...None.