339
FXUS65 KBOI 060802
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
202 AM MDT Sun Sep 6 2026

.KEY MESSAGES...

- Cold front with widespread showers, isolated thunderstorms,
  and gusty winds, coming in from the west late today and
  tonight.

- Breezy and cooler Monday, with showers continuing in the
  north, but becoming sunny in the south.

- Warmer and drier Tuesday through Thursday.

- Windy and cooler with showers Friday.

- Sunny and warmer next weekend.

&&

.SHORT TERM /Through Tuesday Night/...
An upper low is still centered on the OR coast as it has been
since Thursday, and like the last two nights a band of showers
and isolated thunderstorms has set up from nw MT through the
Boise Mountains in ID to north-central NV. As was the case
then, tonight`s band should weaken overnight with showers
ending from south to north before sunrise. But unlike the past
two nights, showers have increased in western and central OR,
and these should continue as the upper low moves inland today.
A surface cold front will take shape in eastern OR this
afternoon with a band of showers and thunderstorms developing
along and just west of it. The front is forecast to move across
the OR/ID border around 5 PM MDT, through the Treasure Valley 5
PM to 8 PM, and Jerome and Twin Falls around 10 PM. In southwest
Idaho the front and wind shift will arrive first, then the
showers. Showers will decrease as the front continues eastward
across the Snake Basin, but frontal winds look stronger east of
BOI with gusts 40 to 50 mph and local blowing dust in the Magic
Valley. On the other hand, showers will increase in central
Idaho along and behind the front this evening, with isolated
thunderstorms and locally heavy rain in Valley and Boise
Counties. The front will exit our CWA overnight but the upper
low and showers will continue in the central Idaho mountains
Monday. Snow level will dip only to 8000 feet Monday so snow
will not be an issue. Total rainfall today through Monday will
be .25 to .50 inch in Valley County/ ID, .10 to .20 inch in
other northern areas and in southern mountains, and less than
.10 inch in southern valleys. These amounts are less than
forecast yesterday. Southern areas will become sunny on Monday
with breezy west winds, and all areas will be at least 10
degrees cooler than today. Latest models show a secondary upper
low in our northern zones Monday night. This low will maintain
clouds in northern zones and breezy west winds in southern zones
through Monday night. Tuesday finally looks sunny and warmer in
all areas as the secondary low moves out.

&&

.LONG TERM /Wednesday through Sunday/...
Warmer and drier Wednesday and Thursday as weak high pressure
aloft rebuilds over the interior western US. Moisture from
westward-moving hurricanes in the Pacific subtropics should
stay well to our south. The next upper trough is forecast in
from BC Thursday night and Friday, which is earlier than
forecast yesterday. As the trough comes closer, southwesterly
flow aloft may tap into tropical moisture and moisten the cold
front now expected in our CWA early Friday. Then after brief
cooling Friday, next weekend looks sunny and warmer again as
an upper ridge builds over the western states.

&&

.AVIATION /06Z Sunday through Monday/...
Issued 1211 AM MDT SUN SEP 6 2026
Generally VFR. Patchy mountain-valley fog/low stratus in the AM.
Scattered showers/isolated thunderstorms moving SW to NE over
southwest Idaho through morning. Then, numerous showers and
thunderstorms moving into E Oregon Sunday afternoon, and into SW
Idaho by evening. MVFR in local heavy rain, and gusty outflows
with storms. Surface winds: variable up to 10 kt, then SW-NW
5-15 kt with gusts to 20-30 kt Sunday afternoon/eve. Except
35-45 kt around KMUO in the evening. Winds aloft at 10kft MSL:
S-SW 10-30 kt.

KBOI...VFR with temporary light rain showers between Sun/06Z-09Z.
Then, a 60% chance of showers and thunderstorms Sunday evening.
Surface winds: NW 5-10 kt, then variable or light SE overnight
and morning.&&

&&

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

OR...None.

&&

$$

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SHORT TERM...LC
LONG TERM....LC
AVIATION.....SH