114
FXUS65 KPIH 020908
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
208 AM MST Tue Dec 2 2025

.KEY MESSAGES...

- Light snow returns during the day and continues into the night
  for most.

- After a break Wednesday, light snow with occasional periods of
  rain returns Wednesday night and continues on and off through
  the weekend.

- Windy to very windy conditions probable Friday afternoon
  through Saturday night for the Snake River plain.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 134 AM MST Tue Dec 2 2025

There is a brief break from precipitation for some this morning,
but the snow and rain mixed with snow returns for the afternoon
and continues through the overnight hours. Snake River plain in
the Interstate 15/86 corridor can expect a half of an inch to an
inch in the populated areas from American Falls to Rexburg.
North of Rexburg, the snow accumulation increases rapidly to
near 2 inches in St Anthony. Very limited areas in the eastern
and southeastern highlands are now expected 6 inches or more for
today and tonight.

There is one proverbial fly in the ointment. A Snake Plain
Convergence Zone event is likely behind this feature that
crosses through in the mid-afternoon. Strong northerly wind will
interact with northwest to west wind from the central Idaho
mountains and the eastern Magic Valley. It appears to be a
strong northerly push that means this event will likely affect
the lower Snake River plain more than the northern end. This
could locally mean intense snowfall for a 1 to 3 hour period
during the early evening hours, around 1700 MST today. Keep an
eye out for this phenomenon if you expect to travel around this
time. It normally starts over the Mud Lake-Terreton area and
drives southward at the same time it intensifies.

Temperatures are trended warmer than the previous forecasts,
with near forty degrees F expected now in the lower Snake River
plain and upper 30s for the upper Snake River plain. Even Sun
Valley will reach 40 degrees F, much to their disliking. Behind
the feature that sweeps through in the afternoon, temperatures
will cool back to the 30s for the lower elevations. This is
likely the coldest high of the week for most locations, with a
warming trend reutrning for Thu. Coldest lows will be tonight
with widespread teens and 20s. A shift in the wind on Thu night
should allow the warming trend to start.

Wind should remain elevated and down right breezy with this
feature that may show up on Thu.


&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Issued at 134 AM MST Tue Dec 2 2025

The longwave pattern is a low amplitude upper level ridge over
the Pacific Northwest and northern Rockies. For Fri, the
forecast area is at the boundary of positive height anomalies
in around 60 percent of the solutions, grouped into two
clusters, while the remainder keep it doubtful; this the
precipitation threat does continue. For Sat afternoon, this
ridge retreats to the southwest and every cluster appears to
have a risk of precipitation. By Sunday, nearly 25 percent of
the clusters have a trough moving through the northern Rockies
and bringing a much better chance of precipitation. But the
majority of the solutions continue this weak precipitation
threat keeping the forecast area at the border of positive
height anomalies with plenty of energy in the upper level stream
to support precipitation. Eastern Idaho is not under the core of
the positive height anomaly on the west coast until Mon. So the
threat of precipitation should nearly disappear for the
beginning of the work week. The good news about this upper level
northwesterly flow is that there is no closed low to dump a
bunch of snow quickly. So snow amounts should be light to
moderate, with the moderate amounts in the mountains and
highlands.

The benefit of being close to the positive height anomalies is
that this means temperatures have to be near to above normal for
afternoon highs. And the cloud cover will keep overnight
temperatures mild Sat highs in the eastern Magic Valley and
lower Snake River plain may approach 50 wet degrees F.

Wind may be the most significant impact from the impulses moving
down this northwesterly upper level flow. Wind Advisory/High
Wind Warning certainly appear very probable for Fri afternoon
through Sat night in the Snake River plain.

&&

.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...Messick
LONG TERM...Messick
AVIATION...01