976
FXUS65 KBOI 180856
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
249 AM MDT Mon Aug 18 2025

.SHORT TERM...Today through Wednesday night...The Flash Flood
Watch in eastern OR was extended until 2 AM PDT as thunderstorms
with moderate to heavy rain continued in northern Malheur County
through Hells Canyon. Radar estimated less than flash-flood rain
amounts but still significant. Radar trends and hi res- models say
the rains will decrease overnight, shift across Valley County/ID
around sunrise, then out of our CWA. Yesterday`s late afternoon and
evening thunderstorms produced a huge amount of cloud-to-ground
lightning in Harney and Malheur Counties, but also wetting rains.
We don`t yet know how many new fires were started, but any fires
will likely grow rapidly as hotter, drier, and windier weather is
expected in those same areas this afternoon and especially Tuesday
afternoon. This will be due to the westward expansion of an upper
high centered in the Four Corners area. High temps will be in the
mid 90s to day and approach 100 degrees in the southern valleys
Tuesday. Also, mid-level monsoon moisture will begin to surge
northward into southern Idaho beginning Tuesday, but not enough
for thunderstorms through Wednesday night.

.LONG TERM...Thursday through Monday...By Thursday enough
monsoon moisture will reach our CWA for a 15 percent chance
of thunderstorms near the NV/ID border. Any storms should have
strong outflow winds but little rain due to low-level dryness.
High temperatures should lower 2-4 degrees by Friday but still
reach the mid 90s in the southern valleys, as a weak upper
trough moves eastward along the Canadian border. Next weekend
looks hotter again, along with another northward surge of
monsoon moisture, this time into southern OR and then eastward
across southern ID, with gradually increasing chances of
thunderstorms, and heightened fire danger due to lightning.

&&

.AVIATION...Mostly VFR, with storms and showers weakening and
moving northeastward out of the area. Local fog development is
unlikely as dewpoints fall this morning. Local visibility
reductions continue in the W-Central ID Mountains due to
wildfire smoke. Surface winds: variable 10 kts or less.
Winds aloft at 10kft MSL: SW 10-20 kt.

KBOI...VFR. Surface winds outside outflows: variable around
5 kt.

&&

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

&&

$$

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SHORT TERM...LC
LONG TERM....LC
AVIATION.....JM