538
FXUS65 KPIH 020552
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
1052 PM MST Mon Dec 1 2025

.KEY MESSAGES...

- Light snow or snow showers will spread across East Idaho
  tonight and continue through Tuesday night. Winter driving
  conditions are expected, especially over mountain passes.

- Daytime highs Tuesday in some lower elevations may limit
  snowfall accumulation potential, and snow may mix with rain in
  some areas.

- The next winter storm arrives Friday and continues into the
  weekend, bringing mountain snow and low elevation rain and
  snow.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 126 PM MST Mon Dec 1 2025

Satellite imagery shows broad area of stratus across East Idaho
beginning to be overtopped by moisture moving in ahead of
shortwave crossing the Seattle/Vancouver area this afternoon.
Seeder-feeder light snows may begin late this afternoon and
evening ahead of main precipitation where the low clouds still
persist, but early accumulations due to this should remain very
light. High-res models remain consistent on timing of bringing
light snow into areas along the Montana border including Island
Park this evening, then slowly expanding precipitation across
the remainder of East Idaho tonight into Tuesday. Given the
northwest flow aloft, the bulk of the precipitation through the
event should be focused across the eastern and southern
highlands, with some shadowing expected across northwest
portions of the Snake Plain. Temperatures daytime Tuesday could
be warm enough across the Magic Valley and Raft River regions to
support a brief mix of rain/snow during the afternoon, and will
limit accumulation potential further north in the Snake Plain.
Total accumulations remain similar to previous forecast cycle,
generally up to an inch for most of the Snake Plain (lower in
the Magic Valley), trending toward 2-3" north toward Monida Pass
and Ashton Hill. Highland areas east of I-15 see accumulations
rise to 4-6" with locally higher amounts at and above pass
level. Further west, lesser accumulations are forecast for the
central mountains, especially for areas shadowed in northwest
flow. To the south highlands between I-84/I-86 and the Utah
border, most of the accumulation will be above valley floors,
with most mountain ranges seeing 3-5" for the event. Given these
amounts, winter headlines will NOT be issued, but motorists
could expect winter travel conditions at times through at least
Tuesday night.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 126 PM MST Mon Dec 1 2025

Will start out dry on Wednesday behind the Canadian system as it
pushes east.   It will be cool with highs in the upper 20s to mid
30s.  Going into the latter part of the week the model blends
indicate getting into a moist more zonal flow.  With that expecting
several waves of precipitation late Thursday through Sunday.  There
will be the potential for mountain snowfall accumulation in this
flow pattern.   We are likely to see substantial warming late week
into the weekend and early next week.  By Saturday snow levels will
likely rise to the 6 thousand foot level so will likely see some
rain in lower elevations with the late week and weekend
precipitation.  Grids indicating the heaviest snow in the eastern
mountains near Wyoming border Friday through Sunday.  At least a low
chance some areas above 6 thousand feet could see 6 inches but
extremely high uncertainty with any timing  and precipitation
amounts that far out into forecast period.  Friday through Monday
expect high temperatures in the 40s in low elevations and 30s to
around 40 in the mountains.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1052 PM MST Mon Dec 1 2025

Most updates for the 06z TAF package are relatively minor as we
continue to "tap and nudge" the going forecast into submission based
on trends...but of particular note...we are starting to get a
clearer, slightly higher confidence idea in where/when snow will
fall with this system. A few snow showers are wrapping up now with a
light/discontinuous first wave...we then have pulled all precip out
of the forecast (except for VCSH at KDIJ) until 17-18z/10-11am
Tuesday, so an organized break under BKN to OVC but VFR cigs. Not
too bad. We then bring back some low-moderate confidence VCSH late
Tuesday morning and Tuesday afternoon but likely still VFR, with
guidance still favoring KDIJ with the best chance of snow showers
(so held onto -SHSN there with some lower cigs). Concern continues
to increase for development of a wind-convergence-induced band of
snow late Tuesday afternoon into Tuesday night (advertised in some
capacity in simulated reflectivity on every hourly CAM) starting in
the KIDA region as early as 22z/3pm, and then sinking SSW through
KPIH and KBYI...all while at least snow showers continue at KDIJ.
This band may feature brief moderate to heavy snowfall rates with
MVFR cigs and IFR vsbys dropping as low as 1-3SM, so a 2-4 hour
period of significant aviation impacts are possible. This band
should not impact KSUN, with only VCSH and VFR conditions forecast
there with moderate-high confidence through Tuesday evening.
Guidance is also suggesting lingering low stratus behind the band at
least for KBYI and KPIH well into Tuesday night/Wednesday morning,
while clouds may break up further north for KSUN and KIDA. Expect a
sudden wind shift from SW to N as well with the band at KIDA and
KPIH. The latest timing for all of this is spelled out in the new
TAFs, and is subject to tweaks as this potentially impactful period
approaches. Previous discussion below.

Issued at 459 PM MST Mon Dec 1 2025

Another day at the aviation desk...yet another shortwave trough
headed our way. This system will drop northwest to southeast across
our region tonight through Tuesday night. We`re having a really hard
time pinning down when and where the best periods of snow showers
will focus in relation to the airports...agreement remains poor
among high-resolution guidance and model simulated reflectivity, and
much of the system seems quite "light and showery" especially in the
CAMs. Approaching this with caution by just slowly
tapping/nudging/trending the ongoing TAF forecasts, with much of
this system currently covered with VCSHs until we can pin down
periods of potentially greater impacts at any given location.
Overall, it`s looking like any periods of lower-than-VFR cigs will
hold off until Tuesday afternoon or evening (although can`t rule out
brief MVFR if organized snow showers strike before then), and models
offer a bit more consensus on the best snow potential happening at
KDIJ so have continued with -SHSN trending -SN there starting after
06z/11pm tonight. We are seeing signs that some more significant
impacts may develop Tuesday late afternoon into late evening as
winds potentially align to generate a convergence-induced band of
snow over the Snake Plain corridor, which may impact at least KIDA,
KDIJ, and KPIH as it sinks south. Timing of this potential right now
looks like it falls after 22-23z/3-4pm, and MVFR to IFR cigs/vsbys
would be possible. We`ll be looking at this closely in future TAF
updates.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM...DMH
LONG TERM...GK
AVIATION...KSmith