849
FXUS65 KBOI 220249
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
849 PM MDT Thu Aug 21 2025

.DISCUSSION...High pressure will continue to build across the
Intermountain West into the Pacific Northwest through early next
week. Mid-level moisture has already begun spreading into the
region along the IdahoNevada border, evident by scattered
cumulus cloud development. The developing ridge to the south
will allow for light diurnal flow and limited mixing across much
of the area tonight through at least Saturday. As a result,
smoke from local fires will be slow to disperse, especially
within mountain valleys.

Satellite imagery shows smoke from the Island Creek Fire near
Elk City, Idaho filtering south through larger valleys into
Valley County as of 8 PM MDT. This smoke will continue moving
southward through the mountain valleys and is likely to reach
the Treasure Valley by sunrise Friday. Some improvement in
smoke/air quality is expected across the Snake River Plain
Friday afternoon with better mixing, but additional smoke is
likely to filter south through the valleys Saturday morning.
Overall, reduced air quality and hazy skies should be expected,
particularly during the morning hours.

No significant changes are expected in the pattern for the
weekend. Thunderstorm potential will increase as monsoonal
moisture spreads into the region. The forecast pattern looks
very active, with the potential for strong outflow winds,
lightning, and blowing dust creating fire weather concerns from
Saturday into Sunday. As moisture continues to increase, with
forecast precipitable water values approaching the 95th to 98th
percentile Monday through Thursday, heavy rain and flash
flooding over burn scars will become a growing concern, in
addition to the potential for strong to severe thunderstorms. No
updates needed at this time.

&&

.AVIATION...Areas of MVFR to LIFR in wildfire smoke in w-central
Idaho including KMYL, creating mtn obscuration. Smoke layers
expanding south into Boise Mtns Friday. Surface winds: variable 10
kt or less, then NE-NW 5-15 kt Fri afternoon. Winds aloft at 10kft
MSL: variable 5-15 kt.

KBOI...VFR. Light smoke layers Friday. Surface winds: variable
around 5 kt overnight, then NW 5-10 kt Fri afternoon.

Weekend Outlook...Mainly VFR. Visibility reductions in w-central
Idaho due to wildfire smoke. A 10-15% chance of
showers/thunderstorms in SE Oregon Saturday PM, then 20-40% chance
of storms near the NV border Sunday PM. Variable 5-15 kt surface
winds, except gusty/erratic winds 35-45 kt near thunderstorms.


&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Saturday night...Dry conditions
prevail through the early this weekend. Temperatures this
afternoon will reach the the low to mid 90s across lower
elevations. A ridge building in over the Four Corners region
will keep our area under dry southwesterly flow aloft. This
building ridge trough supports a warming trend through
Saturday, with lower elevations making it up to the mid-90s on
Friday. Come Saturday, flow aloft will back giving us more of a
southerly component. This supports even more warming with
temperatures reaching near triple digits on Saturday, making it
the warmest day. However, have help off on issuing any headlines
for the time being.

The backed flow aloft brings another consequence along with
it... some monsoonal moisture. While the bulk of this mid-level
moisture will arrive early next week, sufficient moisture (PWATS
around the 75th percentile) will creep into eastern Oregon and
to the Nevada border by Saturday afternoon. This supports a
slight chance (15-20%) of shower and thunderstorms in
southwestern Harney county and along and south of the Nevada
border. With model soundings showing a dry boundary layer, Storms
that develop Saturday afternoon will be high-based (LCLs close
to 500mb or 15000 feet above ground level), this means that
little rainfall will make it to the ground and outflow winds
will become the primary hazard. PWATs will continue to increase
through Saturday night as moisture continues to advect into the
region.


LONG TERM...Sunday through Thursday...Upper ridge over the
interior western US will weaken starting Monday, but cooling will
begin Sunday as monsoon moisture brings clouds from the south.
A slight chance of thunderstorms will begin in southeast Oregon
early Sunday, then expand over most of our CWA Monday through
Thursday.  Gradual cooling through Thursday while the chance of
showers and thunderstorms slowly increases, especially in southern
areas. Initial thunderstorms will bring gusty winds but little
rain due to dryness in the lower atmosphere, but later storms
(Tuesday through Thursday) should be wetter as the lower levels
moisten.

&&

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

&&

$$

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DISCUSSION...JDS
AVIATION.....SH
SHORT TERM...NF
LONG TERM....LC