219
FXUS65 KBOI 121602
AFDBOI

Area Forecast Discussion
National Weather Service Boise ID
1002 AM MDT Tue Aug 12 2025

.DISCUSSION...Expanded the Heat Advisory to include the Upper
Treasure Valley for today as forecast highs trended up slightly
and are expected to be near or slightly above 100 degrees. While
it will be hot, highs are generally expected to remain below
daily records. A weak shortwave trough will move through our
area tonight. While thunderstorm chances remain too low to
include in the forecast, there will be weak elevated instability
across the northern mountains (Baker County OR through the
west-central and Boise mountains), so cannot rule out isolated
shower and thunderstorm development. As a deeper upper level
trough approaches on Wednesday, temperatures will cool a few
degrees in most areas and winds will increase. For additional
details, see the previous discussion.

&&

.AVIATION...VFR. High density altitude this afternoon due to hot
temperatures. Surface winds: Variable up to 10 kt this morning,
Becoming W-NW 8-12 kt this afternoon. Winds aloft at 10kft MSL: SW-
NW 5-15 kt.

KBOI...VFR. High density altitude due to hot temperatures this
afternoon. Surface winds: SE 5-10 kt this morning becoming NW 5-10
kt after Tue/18z.

&&

.PREV DISCUSSION...
SHORT TERM...Today through Thursday night...Heat Advisory will
remain in effect today in Malheur County and the Oregon Lower
Treasure Valley as that`s where models show a surface thermal
pressure trough (representing hottest air) at 6 PM MDT. Hi-res
models also show middle and high clouds developing just west of
the thermal trough axis in southern Harney County late today,
then into southern Malheur County this evening, but not enough
for showers or thunderstorms. However, clouds will keep
temperatures warm through the night in our southern zones,
staying just west of the eastward-moving thermal trough. That
includes the Owyhee Mountains and Southwest Idaho Highlands. By
Wednesday afternoon the thermal trough axis will be east of our
CWA, for slight (2-4 degrees) cooling, along with light to
moderate northwest winds. But south-central Idaho should be as
hot as today. In addition, enough monsoon moisture will reach
south-central Idaho from Nevada late Wednesday for a 15-25
percent chance of thunderstorms with gusty outflow winds.
Thursday looks 6 to 10 degrees cooler than Wednesday in all
areas as a weak north Pacific upper trough comes inland. South-
central Idaho will again have a 15-25 percent chance of
thunderstorms with gusty winds late Thursday, clearing Thursday
night.

LONG TERM...Friday through Tuesday...A strong upper-level low
in the Gulf of Alaska and a building upper-level ridge in the
Four Corners region will drive the pattern. A cold front will
be stalling out in the area on Friday as it accompanies an
embedded shortwave in the flow. This will herald a pattern
change from NW/zonal flow to SW flow aloft. With SW flow aloft,
eventually becoming S flow aloft, monsoonal moisture will be
transported north, raising our PWATs from near 0.6" to 0.8"
areawide. This will be a contributor to conditional thunderstorm
threat during peak diurnal heating Sat/Sun/Mon afternoon and
evening. PoPs at this time limit chances largely to our northern
zones (Valley, Baker, Northern Harney, Northern Malheur counties).
However, other high elevation areas will likely trend higher
with time. This pattern of troughing will keep temperatures near
normal through the extended.

&&

.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Heat Advisory until 9 PM MDT this evening IDZ012-014.
OR...Heat Advisory until 9 PM MDT /8 PM PDT/ this evening
     ORZ063-064.

&&

$$

www.weather.gov/Boise

Interact with us via social media:
www.facebook.com/NWSBoise
www.x.com/NWSBoise

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