710
FXUS65 KBOI 171536
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
936 AM MDT Sun Aug 17 2025

.DISCUSSION...The remnants of yesterdays cold front are
drifting eastward this morning, serving as the focus for light
showers and isolated thunderstorms across southwest Idaho. Radar
has shown activity from Rome, Oregon through the Lower Treasure
Valley into Valley County over the past few hours. Most
locations have received light rainfall (around 0.01), though a
few sites have reported up to a tenth of an inch. This activity
will continue to move east-northeast through the morning, with
more widespread showers and thunderstorms expected by this
afternoon and evening.

Atmospheric conditions remain favorable for scattered
convection today. The 12Z BOI sounding measured a PW value of
1.0, placing moisture near the 95th percentile for mid-August.
Coupled with an approaching shortwave providing added lift and
modest instability of around 600 J/kg, storms will be better
organized and longer-lived than those seen yesterday. Heavy rain
and gusty outflow winds remain the primary threats.

Two primary areas of concern are expected:

*Idaho/Nevada border into the Western Magic Valley: Thunderstorms
 are forecast to initiate near 2 PM MDT south of Twin Falls,
 pushing into the Western Magic Valley by around 4 PM. A
 somewhat drier boundary layer here favors stronger outflow
 winds in addition to heavy rain with the more intense storms.

*Southeast Oregon into Owyhee County: Additional storm
 development is expected around 5 PM MDT, with storms tracking
 northeast into the West Central Mountains and potentially the
 Treasure Valley later tonight. The greatest flash flood risk
 remains over vulnerable burn scar areas across southeast Oregon
 and the West Central Mountains of Idaho where heavier rainfall
 is most likely. Flash Flood Watches remain in effect.

The forecast has been updated to align with current radar trends
and this mornings frontal passage.

&&

.AVIATION...Mostly VFR. Scattered thunderstorms this afternoon
and evening. Storms will produce heavy rainfall, small hail, and
gusty outflows. Local visibility restrictions due to wildfire
smoke in the W-Central ID Mtns. Surface winds: Light and
variable this morning, becoming mostly NW 5-15 kt this
afternoon. Winds aloft at 10kft MSL: SW 10-20 kt.

KBOI...VFR. Isolated showers and thunderstorms this morning
ending by 17z. A 30% chance for thunderstorms later this
evening. Storms could produce heavy rainfall, hail, and 35 kt
outflows. Surface winds outside outflows: NW 5-15 kt.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Tuesday night... A Flash Flood
Watch has been issued for this afternoon and evening over
burn scars in eastern OR and adjacent parts of western ID.
The area corresponds closely to WPC`s excessive rainfall
outlook area. Contributing factors include: a short wave
trough rounding the base of a larger scale upper trough over
the northwestern US, thunderstorms depicted in hi-res forecast
models this afternoon, abnormally high precipitable water
(0.75 to 0.90 inch), significant instability (NAM LI -2 to
-4 and CAPE 600 to 1000 J/KG), greater sunshine than yesterday
leading to steeper lapse rate, and yesterday`s rainfall to
help moisten lower atmospheric layers today. These factors will
continue through this evening, then end overnight. No further
threat is expected Monday as the main upper trough fills and
a hotter and drier upper high builds westward toward our CWA
from the Rockies and Great Basin. However, as early as Tuesday
afternoon circulation around the high will draw monsoon
moisture into southern Idaho from the south. Models are
inconsistent on this so we are keeping Tuesday dry for now
in our forecast.

LONG TERM...Wednesday through Sunday...By Wednesday enough
monsoon moisture should arrive in southern Idaho for at least
a 15 percent chance of thunderstorms near the ID/NV border,
and through the rest of the week as well. The whole period
will be hot with high temps 5 to 10 degrees above normal,
with the upper high centered directly over the Great Basin.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Flash Flood Watch from 3 PM MDT this afternoon through this
     evening IDZ011-012-015-029-033.
OR...Flash Flood Watch from 3 PM MDT /2 PM PDT/ this afternoon
     through this evening ORZ061>064.

&&

$$

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