Area Forecast Discussion
Issued by NWS Boise, ID

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722
FXUS65 KBOI 231616
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1016 AM MDT Tue Jul 23 2024

.DISCUSSION...An upper ridge will maintain the hot temperatures
today. Excessive Heat Warning and Heat Advisories remain in
effect for the lower elevations. Smoke from area wildfires has
been quite extensive, resulting in Air Quality Advisories for
portions of SE Oregon and SW Idaho. Most of the area will remain
dry through this evening, although moisture near the NV border
will lead to a chance (generally less than 30 percent) of
thunderstorms. The storms will be accompanied by gusty outflow
winds to 50 mph. No updates.

&&

.AVIATION...Low VFR/MVFR visibility from smoke, with local IFR
in E Oregon near wildfires. Isolated t-storms near the NV
border and central Idaho after 19Z, with outflow gusts of around
25-35 kt. High density altitude due to heat. Surface winds:
variable 10 kt or less. Winds aloft at 10kft MSL: S-W 5-15 kt.

KBOI...Low VFR in smoke. MVFR smoke should gradually improve
this afternoon. High density altitude due to heat. Surface
winds: variable less than 5 kt becoming NW 5-10 kt after 18Z.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Thursday night...An upper-level
ridge will continue to break down today as an upper-level low
approaches for Wednesday and Thursday. This morning, several new
fires have been detected in Southeast Oregon, particularly in
Baker County, adding to the already significant fire activity.
This will worsen the smoke conditions and poor air quality
across the forecast area today. However, the smoke may slightly
lower temperatures, though they are still expected to reach
102-105 degrees in the valleys.

The best chance for thunderstorms (30%) this afternoon is along
the Nevada border and in the Central Idaho mountains, where
moisture and instability are highest. Some high-resolution
models indicate a weak shortwave moving from southwest to
northeast late tonight into Wednesday morning, which could bring
more showers and thunderstorms, though confidence in this
forecast is low.

Stronger thunderstorms are possible with the cold frontal
passage on Wednesday afternoon and evening, associated with the
large upper-level low off the Pacific Northwest coast. The front
will reach Baker and Harney counties late Wednesday afternoon
and move east-southeast through the night. High precipitable
water values (90th percentile), steep lapse rates, and surface
CAPE approaching 1000 J/KG ahead of the approaching cold front
support stronger, longer-lived thunderstorms capable of
producing 70 MPH outflow winds, brief heavy rain, and small
hail. Thunderstorms will be possible across the entire forecast
area. Although these storms may bring some rain, the outflow
winds and lightning could worsen the current fire situation.
Thunderstorms are expected to redevelop on Thursday across
southwest Idaho as the low moves inland across northern Idaho.

LONG TERM...Friday through Tuesday...A shortwave moves through
on Friday, bringing continued showers and thunderstorms focused
along the ID-NV and OR-NV Friday afternoon and evening. Another
much weaker shortwave brings showers and thunderstorms to the
central Idaho mountains Saturday afternoon and evening, which at
thise point is the last precipitation event before clearer
conditions set in through Tuesday. Afternoon highs are still
forecast to be cooler than the short term, with lower valley
highs remaining below 100. Temperatures will be about normal for
this time of year. While still hot, this should come as much
needed relief from the long- lived heat wave.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Red Flag Warning from noon Wednesday to midnight MDT Wednesday
     night IDZ400>403-420-421-423-424-426.
     Excessive Heat Warning until 9 PM MDT Wednesday IDZ012-014-033.
     Heat Advisory until 9 PM MDT Wednesday IDZ015-016-029-030.
OR...Red Flag Warning from noon MDT /11 AM PDT/ Wednesday to
     midnight MDT /11 PM PDT/ Wednesday night ORZ636-637-646.
     Excessive Heat Warning until 9 PM MDT /8 PM PDT/ Wednesday
     ORZ063-064.
     Heat Advisory until 8 PM PDT Wednesday ORZ061-062.

&&

$$

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