FXUS65 KBOI 182042
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
242 PM MDT Mon May 18 2026

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

&&

$$

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SHORT TERM...DG
LONG TERM....NF
AVIATION.....NF