FXUS65 KBOI 181755
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1155 AM MDT Mon May 18 2026

.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 /18Z Monday through Tuesday/...
Issued 1155 AM MDT MON MAY 18 2026

VFR. Scattered showers this afternoon, mainly across higher
terrain. Brief MVFR/IFR conditions and mtn obscuration in
showers. Snow levels: 5.5-6.5 kft MSL. Surface winds: W-N 5-15
kt with gusts to 20-25 kt this afternoon. Becoming variable 5-10
kt overnight. Winds aloft at 10kft MSL: N 10-20 kt. 

KBOI...VFR. Showers over the foothills this afternoon. Surface
winds: NW 10-20 kt with gusts up 28 kt this afternoon, becoming
SW-NW up to 8 kt overnight. 

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.

OR...None.

&&

$$

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AVIATION.....NF
SHORT TERM...JDS
LONG TERM....SA