471
FXUS65 KBOI 210913
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
313 AM MDT Fri Jun 21 2024

.SHORT TERM...Today through Sunday night...Satellite this
morning shows an upper-level trough over northern Idaho, which
will move east into Montana this afternoon. This shift will
bring drier air and westerly flow aloft, limiting warming across
the forecast area. Temperatures are expected to rise by about
2-4 degrees above yesterdays highs. While moisture will be
limited, there will be enough to support cumulus cloud
development across southwest Idaho.

The next Pacific system is set to reach the British Columbia
coast on Saturday, potentially bringing the warmest temperatures
of the year so far. Forecast models now indicate a 50-70%
chance of temperatures reaching 100 degrees or more in the
Treasure Valley on both Saturday and Sunday. Historically,
Boise`s first 100-degree day occurs around July 9th, though in 5
of the last 11 years, it has happened in June.

.LONG TERM...Monday through Friday...A brief break in the hot
temperatures is expected on Monday with the passage of a Pacific
system. Although the core of the system will remain well north
in Western Canada, an associated surface cold front will move
across the forecast area, bringing slightly cooler temperatures.
Highs will drop into the mid-90s on Monday. The air mass will
remain too dry for any precipitation with the frontal passage.

A much stronger Gulf of Alaska trough is expected to move
inland, potentially as early as Thursday. The latest ensemble
guidance shows much better agreement, with 93% of the members
favoring a Thursday/Friday timing for the cold frontal passage.
This setup will build a ridge across the forecast area for
Tuesday into Wednesday, bringing back the hot temperatures.
Current guidance indicates temperatures between 99-101F for the
Treasure Valley. However, these temperatures could be too low
due to the likelihood of stronger east-southeasterly winds ahead
of the approaching cold front. Although guidance does not
currently show these winds, they are typical with this type of
synoptic pattern. Temperatures will drop about 20-25 degrees
behind the front, potentially leading to below-normal
temperatures on Friday. While the air mass will remain largely
dry, there could be enough moisture across our northern mountain
zones for showers and thunderstorms on Friday.

&&

.AVIATION...VFR. Mostly clear skies. Surface winds: E-SE 5-15
kt. Winds aloft at 10kft MSL: S-SE 10-15 kt.

KBOI...VFR. Mostly clear skies. Surface winds NW 5-10kt,
switching to SE 5-10kt around 21/06Z.

Weekend Outlook...VFR. Hot temperatures will bring high
density altitudes Saturday and Sunday. Surface winds W-SW
10-20kt during the afternoons, light during the night.

&&

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

&&

$$

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SHORT TERM...JDS
LONG TERM....JDS
AVIATION.....JDS