Flash Flood Warning 9, NWS Boise, ID

Area Forecast Discussion
National Weather Service Boise ID
234 PM MDT Tue Aug 26 2025

.SHORT TERM...Tonight through Thursday night...
A very moist atmosphere remains in place as southerly flow
transports monsoon moisture over the forecast area. The morning
sounding measured 1.20 inches of precipitable water with light
southerly steering flow. This is a favorable setup for slow moving
showers and thunderstorms and locally heavy rain, thus a flash
flood watch remains in effect. Showers and thunderstorms will
be on the uptick late this afternoon and evening, continuing
overnight and Wednesday. Greatest coverage is expected across
southwest Idaho as a weak upper trough lifts slowly north across
the area tonight and Wednesday. Westerly flow on the back side
of the trough is forecast to bring drier air into SE Oregon late
tonight which will diminish the precipitation chances over
Harney County by Wednesday morning. Therefore the flash flood
watch was adjusted to end late tonight for Harney County but
continues elsewhere through Wednesday evening. Westerly flow and
drier more stable air will spread across the area Thursday as
the upper trough departs and ridging starts to build over the
area. This will limit the chance of showers and thunderstorms to
primarily the higher terrain across SW Idaho Thursday while
temperatures trend up.

.LONG TERM...Friday through Tuesday...A broad upper ridge will build
into the region by Friday resulting in a warming and drying trend
heading into the weekend. High temperatures in the lower valleys are
expected to return to the upper 80s and lower 90s Friday to Sunday,
a few degrees above normal. Model guidance shows an upper low along
the Pacific NW coast early next week. There is currently a strong
guidance disagreement on whether the aforementioned upper low will
either split off or remain quasi-stationary over the NW coast by
Tuesday. This may bring (20% chance) some showers/thunderstorms
early next week over the mountains of SW Idaho.

&&

.AVIATION...Showers/thunderstorms becoming scattered to numerous
late this afternoon and evening. Greatest coverage across SW Idaho.
Outflow gusts to 25-35 kt, heavy rain, and small hail possible. MVFR
to local IFR conditions and mtn obscuration in heavy rain.
Visibility reductions near mtn wildfires. Surface winds: variable 5-
15 kt. Winds aloft at 10kft MSL: variable 5-15 kt.

KBOI...VFR. Scattered to numerous showers/thunderstorms in Treasure
Valley late this afternoon with 30-40 percent chance of impacting
the airport. Outflow gusts to 25-35 kts, mod/heavy rain, and small
hail possible. Then, rain showers likely (70-80% chance) at KBOI
tonight through Wednesday. Showers may be heavy at times and create
MVFR visibility. Surface winds: variable 10 kt or less through
tonight.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Flash Flood Watch through Wednesday evening
     IDZ011>016-028>030-033.
OR...Flash Flood Watch through Wednesday evening ORZ062>064.
     Flash Flood Watch through late tonight ORZ061.

&&

www.weather.gov/Boise

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SHORT TERM...TL
LONG TERM....TL
AVIATION.....TL

Special Weather Statement
National Weather Service Boise ID
553 PM MDT Tue Aug 26 2025

IDZ013-014-270030-
Upper Treasure Valley ID-Boise Mountains ID-
553 PM MDT Tue Aug 26 2025

...STRONG THUNDERSTORMS WILL IMPACT NORTHERN ADA...SOUTHWESTERN BOISE
AND WEST CENTRAL ELMORE COUNTIES THROUGH 630 PM MDT...

At 552 PM MDT, Doppler radar was tracking a cluster of strong
thunderstorms over Lucky Peak Reservoir, or 9 miles east of Boise,
moving northwest at 15 mph.

HAZARD...Wind gusts up to 40 mph. Outflow winds expanding into Boise
         metro.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Areas of blowing dust possible.

Locations impacted include...
Boise, Eagle, Garden City, Blacks Creek Reservoir, Arrowrock Dam,
Lucky Peak Dam, Lucky Peak Reservoir, Lucky Peak Spring Shores
Marina, and Arrowrock Reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 4346 11579 4338 11612 4366 11644 4377 11591
TIME...MOT...LOC 2352Z 147DEG 12KT 4357 11605

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...40 MPH

SH

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