832
FXUS65 KBOI 220236
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
836 PM MDT Mon Jul 21 2025

.DISCUSSION...Thunderstorms with heavy rain and small hail
developed in eastern Oregon this afternoon and early evening
behind a cold front clearly evident on satellite imagery in
western Idaho. We issued a Flash Flood Warning for heavy rain
from thunderstorms that passed over the Durkee Fire Burn Scar
in northern Malheur County and southwest Baker County this
afternoon, but as of 630 PM PDT all thunderstorms were east of
the area and weakening. The cold front and thunderstorms were
due to an upper trough over the northwest US that will stretch
NE-SW and weaken overnight and Tuesday. Showers will decrease
tonight, and fewer showers and afternoon thunderstorms will
re-develop Tuesday afternoon, and those mainly over the central
Idaho mountains and southern mountains near the dissipating
cold front. Temperatures will also start to rise Tuesday.
Due to today`s rain we now expect patchy fog Tuesday morning
in the eastern Oregon valleys. Otherwise the current forecast
is on track.

&&

.AVIATION...Scattered thunderstorms with moderate/heavy rain,
local MVFR-IFR, and mountain obscuration across e-central
Oregon and the w-central Idaho mountains late this evening.
Decreasing storms after sunset, but light precip and virga
lingering over SW and central Idaho into Tue AM. In addition,
local IFR in fog in e-central Oregon valleys Tuesday morning.
Surface winds: NW 5-15 kt, then variable 10 kt or less. Winds
aloft at 10kft MSL: W 10-20 kt.

KBOI...VFR. A 15% chance of light rain tonight into Tue
morning. Surface winds variable or NW, up to 10 kt.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Wednesday night... A band of
showers continues to move east into southwest Idaho as a
cold front moves east. This band brought a good amount of rain
to eastern Oregon, with Baker City having already broken its
daily rainfall record (receiving just over half an inch as of
writing this). Precipitation will begin to taper off with this
band as it continues to move east. Gusty winds are expected to
continue through the day, with gusts up to 35 mph between Twin
Falls and Boise. A few thunderstorms have already developed west
of Harney/Baker counties behind the cold front. As the airmass
continues to recover this afternoon, more isolated storms will
develop in eastern Oregon. Good kinematics are in place with
current RAP meso-analysis showing 50-60 kts of 0-6km shear.
This shear, paired with mixed layer CAPE increasing to around
500 j/kg as the surface destabilizes, would allow for a
potential of strong storms that can sustain themselves. The
main hazards for storms that develop are outflows of 45mph,
and localized heavy rain. The isolated nature of the storms
and their forward speed is helping to mitigate the risk of
flash flooding for burn scars; however, if a thunderstorm does
cross over a burn scar in eastern Oregon, flash flooding is not
out of the picture.

Overnight tonight, the cold front will stall out across out
area. Where this front ends up will dictate what areas will have
a chance of overnight/morning showers Tuesday. As of now, the
most likely area for this to occur is between Boise and Twin
Falls. Precipitation chances overnight into early Tuesday stay
between 15-20% southeast of a line from Boise and Lowman, and
northwest of a line from Bruneau and Mtn Home. Tuesday
afternoon, our area stays under southwest flow aloft as the
trough that sent the cold front through will begin to close
off into a upper-level low and sit off of the coast of
California. This will allow for a 15-40% chance of precipitation
across much of our area (highest chances being near the Nevada
border), as well as a 15-20% chance of thunder across Higher
terrain and north of the nevada border. The threat of
showers/thunder returns Wednesday afternoon north of the Nevada
border. Temperatures take on a warming trend beyond today, but
stay 10-15 degrees below normal through Wednesday.

LONG TERM...Thursday through Monday...The active pattern
continues through Sunday as deterministic and ensembles models
are in good agreement of our area remaining under southwest flow
aloft. This allows for daily chances of afternoon thunderstorms
through Sunday afternoon, primarily in eastern Oregon and along
the Nevada border. Late this week, the upper-level low should
embed itself back into the main flow aloft and move over our
area. Although a building ridge over the Great Plains will keep
our area under southwest flow aloft. Temperatures will warm to
near normal by Thursday, and then hover within a few degrees of
normal Through Monday.

&&

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

&&

$$

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