textproduct: Boise

UPDATE

Updated aviation discussion.

KEY MESSAGES

- Mountain showers on Monday, otherwise dry, breezy and slightly warmer.

- Dry with temperatures warming back above normal starting on Wednesday.

SHORT TERM /Through Wednesday Night/

Issued 257 AM MDT MON MAY 18 2026 The tight surface pressure gradient behind an eastward exiting low pressure system will continue to generate breezy northwest winds today across much of the area. Wind gusts between 25 and 35 mph can be expected this afternoon, though they will not be quite as strong as what was observed on Sunday. While a stable air mass dominates the lower elevations, lingering afternoon instability will support a slight chance of light showers over the mountains today, with minimal accumulation expected.

Northwest flow aloft will carry into Tuesday as high pressure builds over the Pacific. A more stable and dry air mass will keep conditions clear across the region, allowing temperatures to warm back to near normal values for this time of year.

By Wednesday, an embedded shortwave trough will move through the intermountain west, tracking across our area into Wednesday night. This system will bring an increase in cloud cover along with light, isolated showers primarily focused across the West Central Mountains of Idaho. The arrival of this shortwave and its associated cloud cover will also work to slow down the overall warming trend as we transition into the long term period.

LONG TERM /Thursday through Monday/

Issued 257 AM MDT MON MAY 18 2026 A trough over Montana will dig into southern Idaho on Thursday, bringing cooler temperatures and a slight chance of high terrain showers (10-20% chance). This trough will quickly move east on Friday, bringing a return to dry northwest flow through Saturday with temperatures 5-10 degrees above normal. A weak shortwave passage will bring another low chance of showers over high terrain late Saturday into Sunday, but forecast confidence is very low. By Sunday, a ridge of high pressure will build into the region, bringing warm and dry conditions ahead of a strong upper level low diving down off the British Columbia coast. Models diverge substantially on the path of this upper level low early next week, with some members (ECMWF) bringing this low directly over the region by Monday evening. Current forecast does not favor this outcome, with a strong bias towards the warm and dry scenario on Monday.

AVIATION /12Z Monday through Tuesday/

Issued 539 AM MDT MON MAY 18 2026

Generally VFR. Patchy fog/stratus in sheltered mtn valleys through morning. Scattered showers redevelop Monday PM across E Oregon and mtns of SW Idaho. Brief MVFR/IFR and obscuration in mtn precip. Monday snow levels: 5500-6500 ft MSL. Surface winds: W-N 10-20 kt with areas of gusts to 20-25 kt. Winds aloft at 10kft MSL: N-NE 20- 35 kt.

KBOI...VFR. Foothill showers return Monday PM. Surface winds: NW 10-18 kt with gusts around 25 kt, decreasing to SW-NW 4-8 kt after Tues/03Z.

BOI WATCHES/WARNINGS/ADVISORIES

ID...Freeze Warning until 8 AM MDT this morning for IDZ016. OR...None.