Challis, Idaho Weather Forecast Discussion

362
FXUS65 KPIH 101729
AFDPIH
Area Forecast Discussion
National Weather Service Pocatello ID
1129 AM MDT Wed Sep 10 2025
.KEY MESSAGES...
- Unsettled pattern continues with showers and storms much of
  this week.
- Breezy and warm today, with below normal temperatures
  beginning Thursday.
&&
.SHORT TERM /THROUGH THURSDAY/...
Issued at 249 AM MDT Wed Sep 10 2025
The low pressure system situated over CA/OR/NV will very gradually
begin to shift inland over the course of the next few days. High
resolution models indicate the bulk of shower and storm activity
remaining just outside of Southeast Idaho, with only isolated
activity expected along the borders of our CWA this afternoon.
Heading into later night, models show varying degrees of nocturnal
activity in the central mountains and eastern highlands regions.
HREF probability of thunder dramatically increases just outside of
our CWA in western Idaho this evening, during which time
thunderstorm wind gusts to around 45 mph are shown working into the
eastern Magic Valley region. Beginning around Midnight tonight,
there is decent consensus amongst hi-res models that a round of
organized showers will lift northward into the southeast and eastern
highlands from Utah, with around a 10 to 20 percent chance of
lightning overnight and gusts up to 40 mph. Outside of
thunderstorms, wind gusts look to largely remain under 30 mph.
Daytime temperatures will be within a few degrees of what was
observed yesterday, with highs in the upper 70s to low 80s in our
valleys and 60s and 70s in the mid- to high elevations.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 139 PM MDT Tue Sep 9 2025
The long term period of the forecast looks to remain unsettled as an
upper level low slowly spins across the region later this week and
into the weekend. This will usher in a prolonged period of cooler
temperatures along with daily shower/storm chances throughout
eastern Idaho. Seems like the higher terrain regions have the better
rain chances on any given day but valley locations will not be
removed entirely from the rain chances. They`ll just be a bit lower.
Best chances each day will be primarily during the afternoon/evening
hours but given the pattern, can`t completely rule at least a stray
shower out at any given time. With clouds and precip expected to be
prevalent, along with lower H5 heights in association with the low,
temperatures will generally top out in the 60s and 70s each day
throughout all of eastern Idaho. Despite the cooler daytime highs,
overnight lows won`t be all that chilly as more moisture and cloud
cover will tend to insulate the area from ideal radiational cooling
so lows mainly in the 40s and 50s are expected outside of the
normally colder spots like near Stanley and Copper Basin. As we get
into early next week, models show the potential for another low to
move into the Pacific NW although not seeing much in the way of
model consistency with the timing and placement of this feature.
Nevertheless, certainly seems like the general pattern is trying to
shift away from summer and move into autumn.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1126 AM MDT Wed Sep 10 2025
The bulk of isolated thunderstorm activity today looks to remain
outside of our forecast terminals. However, it`s a non-zero chance
for an outflow from thunderstorms to move through the KBYI and KSUN
areas between 8 PM and 1 AM. Those outflow winds would most likely
be around 35 to 40 kts. It will be a bit breezy outside of storms
today, too, with gusts around 20 to 25 kts. We will be watching for
some spotty showers overnight moving north out of Utah and passing
through DIJ after midnight, so have added some VCSH to the TAF
there. As the low moves farther east tomorrow, isolated storm
chances will increase for our TAF sites.
&&
.FIRE WEATHER...
Issued at 139 PM MDT Tue Sep 9 2025
South to southwest upper flow continues over the region today
keeping temperatures warm with continued shower and storm chances
the next few days. Later tomorrow and especially on Thursday, an
upper low is poised to move over the area and remain in place
through late week and into the weekend. This will bring a prolonged
a period of cooler temperatures and daily precipitation chances.
Highest precip chances will be across the higher terrain areas but
can`t rule out valley precip either. As this low departs later in
the weekend, models try to bring another one into the Pacific NW
early next week but still a bit of uncertainty on the placement and
timing of this feature.
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Cropp
LONG TERM...McKaughan
AVIATION...AMM
FIRE WEATHER...McKaughan

NWS PIH Office Area Forecast Discussion