844
FXUS65 KBOI 230523
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1123 PM MDT Tue Sep 22 2026

.UPDATE...Updated aviation discussion.

&&

.KEY MESSAGES...
- Chance of showers and thunderstorms late this afternoon and
  early this evening, mostly across the high terrain of
  southwest Idaho.

- Warm temperatures through Thursday, with values 10 to 15
  degrees above normal Thursday along with increasing southerly
  winds.

- Cold front passage Friday with cooler temperatures heading
  into this weekend and a chance of precipitation across
  northern portions of the forecast area Friday.

&&

.SHORT TERM /Through Thursday Night/...
Issued 216 PM MDT TUE SEP 22 2026
An upper level low over northern Nevada and Utah will aid in
shower and isolated thunderstorm development late this
afternoon. The best chance of showers and thunderstorms (20-40%)
will be across eastern portions of the forecast area, mainly
east of a line from McCall to Mountain Home. Gusty outflow winds
up to 45 mph possible near showers and thunderstorms, alongside
lightning, small hail, and brief moderate-heavy rainfall.
Showers will diminish this evening with the loss of daytime
heating while the low moves northeast across eastern Idaho.

Dry west to southwest flow will be over the area Wednesday with
the flow aloft becoming more southwesterly by Thursday ahead of
a strong longwave Pacific trough. Thus, temperatures will
generally be on an upward trend Wednesday, and then warm sharply
from Wednesday to Thursday. Temperatures will be 10-15 degrees
above normal on Thursday, with many lower valleys forecast to
see maximum temperatures in the low-mid 90s. Ahead of the
approaching trough, winds in the Snake Plain will increase to
SE 15 to 25 mph with gusts up to 35 mph. Elevated fire weather
conditions will develop Thursday afternoon across SE Oregon and
SW Idaho due to hot, dry, and windy conditions in southerly flow.
Breezy to windy conditions will continue Thursday night ahead
of the Pacific trough and approaching cold front.

&&

.LONG TERM /Friday through Tuesday/...
Issued 216 PM MDT TUE SEP 22 2026
The well advertised cold front is still on track to cross over
the area come Friday afternoon into Friday night. This frontal
passage will be mostly dry, with the wind being the main story.
Southwesterly prefrontal winds will increase with gusts to 25-45
mph. The higher end of that range will be felt generally south
and west of the Snake Plain and across ridgetops. As the front
moves through the area, winds will switch to be out of the
northwest, with post-frontal gusts remaining elevated at 25-40
mph. With the associated trough swinging north of our area, the
best precipitation chances/totals remain on track to stay
generally north of our area. For our area, the best chances of
precipitation (20-40%) will be in northern portions of Baker and
Valley Counties. The temperature effects of this front will be
most felt in eastern Oregon, where it will move through earlier
in the afternoon, with a nearly 20 degrees temperature
difference between Thursday afternoon and Friday afternoon
highs. Above normal temperatures will persist friday across SW-
Idaho, with max temps in lower elevations reaching the low to
mid-80s.

Temperatures will cool to 5-15 degrees below normal area-wide come
Saturday. A trough digging off the west coast will pass-over the
area late Sunday/early Sunday along with an associated cold front.
While this trough and front will be weaker than that of Friday, it
will help keep cooler conditions and breezy west/northwest winds in
place into the start of the next week. Moisture availability is in
question for this next system. With an active eastern Pacific,
tropical moisture could work it`s way back up to support
precipitation chances. However, return flow will be limited with the
quick one-two punch of these systems. Right now, am leaning towards
another dry frontal passage with moisture remaining south and east
of our area. Long-range guidance doesn`t handle the energy transfer
with tropical systems the best, but things should become more clear
in the days to come.

&&

.AVIATION /06Z Wednesday through Thursday/...
Issued 1122 PM MDT TUE SEP 22 2026
VFR. Patchy fog / low stratus is likely overnight in areas that
received rainfall, particularly near KJER, KGNG, and KBKE. Surface
winds: variable under 10 kt overnight. Winds aloft at 10kft MSL:
W 5-15 kt.

KBOI...VFR. Surface winds: S-SE 3-8 kt overnight.

&&

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

OR...None.

&&

$$

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AVIATION.....JM
SHORT TERM...TL
LONG TERM....NF