502
FXUS65 KBOI 190256
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
856 PM MDT Thu Jul 18 2024

.DISCUSSION...Showers continue across eastern Owyhee County and
southern Twin Falls County this evening, but there has been no
lightning observed over the past few hours. Smoke has become
very thick over a larger percentage of the sky compared to the
last few days, and air quality at the surface is also worse. It
is becoming increasingly likely that the smoke will lower our
expected high temperatures over the next few days. However,
extreme heat will still occur (it`s that hot, folks), so the
Excessive Heat Warnings and Heat Advisories will be kept in
place. Finally, the Red Flag Warning expires soon, and the
forecast supports letting it go. No changes are planned at this
time.

&&

.AVIATION...Low VFR/MVFR and local IFR visibility in wildfire smoke.
High density altitude due to hot daytime temperatures.
Isolated/scattered showers and thunderstorms after Fri/18Z, mainly
over south-central/central Idaho terrain. Surface winds: variable 10
kt or less, except NW 10-15 with 20-25 kt gusts for KBKE/KBNO to
KONO tonight. Winds aloft at 10kft MSL: variable 5-15 kt.

KBOI...Low VFR to MVFR visibility from wildfire smoke. High density
altitude due to hot daytime temperatures. Surface winds: becoming SW-
SE around 3-6 kt overnight, then NW 5-10 kt after Fri/18Z.


Weekend Outlook...Wildfire smoke will promote low VFR/MVFR to local
IFR visibility. Isolated thunderstorms on Saturday afternoon mainly
near NV border, then isolated/scattered thunderstorms Sunday
afternoon mainly over E Oregon and higher terrain of SW Idaho.
Surface winds: NW-NE 5-15 kt Saturday during the afternoon, and
variable 5-15 kt Sunday.

&&

.PREV DISCUSSION...
SHORT TERM...Tonight through Saturday night...The upper level
ridge will continue to expand over the West, reaching far into
northern Alberta. Extremely hot, above normal temperatures will
continue through most of the region, with the hottest temperatures
expected in the Snake River Valley. Most valley locations will
confidently exceed 100F for daytime highs through the short term
period, while mountain locations will be in the upper 80s to low
90s.

In addition to hot and dry surface conditions, pushes of monsoon
moisture will bring fire weather concerns for the ID-NV border and
the Boise Mountains this afternoon and Saturday afternoon. Models
highlight showers and thunderstorms this evening mainly near the ID-
NV border (10-20% chance), with gusty outflow winds to 40-50 mph,
lightning, and brief heavy rain. Drier conditions will lower the
chances of convection on Friday, but Saturday afternoon-evening
looks to see another push of high based thunderstorms and showers
over southeast Oregon and southern Idaho. These storms could be
slightly stronger due to enhanced instability from hotter daytime
temperatures on Saturday.

Wildfires in Oregon will continue to bring widespread smoke to the
region, with high Air Quality Index (AQI) values triggering air
quality alerts in Harney and Malheur counties. Smoke models
show smoke mostly staying to the west and east of the Treasure
Valley, although hazy skies will continue through the week for
the region.

LONG TERM...Sunday through Thursday...The ridge will stay
locked into place over the region for most of the long term period,
with a steady warming trend on deck through Monday. A shortwave
trough off the PNW coast looks to reduce temperatures by about 5
degrees on Tuesday, so have dropped the Excessive Heat products for
the area by Monday night. Depending on the eventual track of the
low, the heat products might need to be extended for some locations.
The ridge will amplify to it`s peak on Sunday, bringing the
highest temperatures of the week to the region. Temperatures
will near 110F in the Lower Treasure and portions of the Upper
Treasure Valley on Sunday afternoon.

The monsoonal push looks to continue on Sunday, with continued fire
weather concerns for southeast Oregon and the Central ID Mountains
that afternoon-evening. Long term deterministic models show this
trend continuing each afternoon through the long term period,
although confidence is low on extent and location of
precipitation.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Excessive Heat Warning until midnight MDT Monday night
     IDZ012-014-033.
     Red Flag Warning until 9 PM MDT this evening IDZ423-426.
     Heat Advisory from noon Saturday to midnight MDT Monday night
     IDZ015-016-029-030.
OR...Excessive Heat Warning until midnight MDT /11 PM PDT/ Monday
     night ORZ063-064.
     Heat Advisory from 11 AM Saturday to 11 PM PDT Monday ORZ061.
     Excessive Heat Warning from 11 AM Saturday to 11 PM PDT Monday
     ORZ062.

&&

$$

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DISCUSSION...SP
AVIATION.....SP
SHORT TERM...SA
LONG TERM....SA