453
FXUS65 KBOI 231501
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
901 AM MDT Sun Jun 23 2024

.DISCUSSION...Temperatures across the valley are already in the
low to mid 70s this morning, with the Boise airport at 79F as
of 8:55AM MDT. Temperatures will steadily climb through the day
bringing well above normal temperatures to most of the region.
Most of the lower Treasure Valley will reach the upper 90s to
low 100s. Breezy westerly winds will return by the afternoon as
the upper level pressure gradient tightens due to a trough
passage to the north. The highest winds (W-NW 20-30 mph) will be
on ridgetops and above ~5000 feet. These winds, dry conditions,
and hot temperatures will allow for active fire behavior on
existing fires, promoting more smoke and haze development,
especially across the Owyhee Mountains, with the smokiest
conditions likely downstream near Mountain Home. Conditions will
remain hot and dry through early next week with a slight chance
of showers near the ID-NV border on Tuesday. No forecast
updates necessary.

&&


.AVIATION...VFR with clear skies. Hot temperatures will bring high
density altitudes. Reduced visibilities from smoke near a prescribed
fire in far SW Idaho. Surface winds: variable 10 kt or less becoming
W-SW 10-20 kt with gusts to 30 kt after 18Z. Winds aloft at 10kft
MSL: W-SW 15-30 kt.

KBOI...VFR with clear skies. Hot temperatures will bring high
density altitudes. Surface winds: NW 5-10 kt.


&&

.PREV DISCUSSION...
SHORT TERM...Today through Tuesday night...Temperatures in the
Treasure Valley could reach 100 degrees again today. However,
the arrival of the next Pacific system moving inland across
British Columbia will increase westerly flow aloft, leading to
breezy northerly surface winds in the valley and westerly winds
elsewhere. Expect wind gusts of 25-35 mph in higher elevations,
while winds will be lighter in lower elevations. This setup is
likely to result in slightly cooler temperatures today. Ensemble
probabilities for temperatures reaching 100 degrees or higher
are between 30-70%, with Ontario having the highest probability
at 70% due to warmer surface temperatures from northerly
downslope winds. Hot, dry, and breezy conditions will promote
active fire behavior this afternoon, potentially causing smoke
plumes and hazy conditions, especially east-northeast of the
fire in southwest Owyhee County.

As the Pacific system continues east across West-Central Canada
on Monday, a surface cold front will pass through, bringing
cooler temperatures with valley highs around the mid-90s.
However, the air mass will remain too dry for any precipitation
with the frontal passage.

A stronger Gulf of Alaska trough will approach the Pacific
Northwest coast on Tuesday, causing the upper-level flow to
shift to south-southwest, bringing hot temperatures back to the
forecast area. Ensemble guidance indicates a 25% chance of high-
based moisture from the southwestern U.S. reaching the
Idaho/Nevada border Tuesday night, potentially leading to
thunderstorms. Temperatures in the Treasure Valley will again
approach 100 degrees on Tuesday, with a 20-30% chance of
reaching or exceeding 100 degrees.

LONG TERM...Wednesday through Sunday...The Gulf of Alaska
trough will move inland across western Canada and the Pacific
Northwest on Wednesday, keeping the forecast area in the warm
sector for another hot and mostly dry day. The southerly flow
might bring enough high-based moisture for afternoon
thunderstorms in south-central Idaho. The associated cold front
is expected to reach the forecast area on Thursday, bringing
significantly cooler temperatures and breezy westerly winds. A
temperature drop of about 20-25 degrees is possible, which could
result in below-normal temperatures on Thursday and Friday.
There is around a 90% chance that temperatures will remain below
90 degrees on both days. While the air mass will remain mostly
dry, there could be enough moisture in the West Central
Mountains of Idaho for showers and thunderstorms on Thursday and
Friday. The strongest winds are expected on Thursday with the
passage of the upper-level trough and jet. Temperatures will
rebound into the low 90s next weekend as another ridge develops
in response to another Pacific trough.

&&

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

&&

$$

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DISCUSSION...SA
AVIATION.....BW
SHORT TERM...JDS
LONG TERM....JDS