721
FXUS65 KPIH 042112
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
212 PM MST Thu Dec 4 2025

.KEY MESSAGES...

- Moderate to heavy mountain snow through Saturday morning,
  mainly across the eastern and southern highlands. Winter Storm
  Warning is in effect.

- Light snow tonight for portions of the Snake River Plain, but
  warmer temperatures expected to change precipitation to rain
  or a rain/snow mix.

- Windy late Friday through Saturday. Gusts could approach 40
  mph at times.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 212 PM MST Thu Dec 4 2025

Complicated forecast is unfolding for the next 48-72 hours.
Satellite imagery shows wet northwest flow in place across the
PacNW this afternoon. Shortwave features embedded in the flow on
tap to bring a significant increase in precipitation to East
Idaho starting late this afternoon through this evening, and
continuing into the weekend. Confidence is high regarding
precipitation becoming widespread over higher elevations
overnight tonight, continuing through Friday night, and
beginning to wane on Saturday. Shadowing is expected across
portions of the Snake Plain, including the INL, where northwest
flow would provide a downsloping effect. There is also high
confidence that these systems will advect SOME warm air to the
region, raising snow level elevations, but much lower confidence
on how much warm air and where the snow level will actually end
up.

Models remain quite consistent in the amount of liquid
precipitation expected, especially through Friday night. Looking
at the HREF values, the mean supports 0.30-0.40" water along
the I-15/US-20 and I-84/86 population corridors, dropping to
0.20-0.30" at the lower end but rising to 0.50-0.75" at the
higher end. Some of this will fall as snow TONIGHT THROUGH EARLY
FRIDAY, but this is where the incoming warmer air causes a
problem. Areas from the Eastern Magic Valley northeast to about
Blackfoot will see daytime highs Friday warm to above freezing,
and thus we should see an introduction of rain/snow or a
changeover to all rain during the day. Prior to the warm up, the
areas between roughly American Falls and Rexburg may see 1-4"
of snowfall (higher amounts north of Idaho Falls), which could
impact the Friday morning commute. Snow levels rise with the
incoming warmer air to between 6000 and 7000 ft, but the
uncertainty on timing and amount keeps the rain/snow level much
lower. Some of this will be due to precipitation and existing
snow pack helping to keep lower elevations cooler than models
(particularly the GFS and derivatives) want to warm it. Have
nudged daytime highs slightly lower Friday with expectations of
slightly slower warming. Once the changeover occurs,
precipitation should stay rain or a rain/snow mix at lower
elevations for the remainder of this event.

For the eastern and southern highlands, model guidance has
fluctuated slightly in liquid amounts, but the consensus remains
similar: HREF indicates snowfall rates will approach 1"/hr at
times tonight, and then again late Friday into Friday night.
Liquid QPF means through Saturday generally exceed 0.50" but
could range as low as 0.30" and could exceed 1.50" across the
Bear River Range. This results in snow accumulations that exceed
a foot in most higher elevation areas above 6000 ft. Ridge tops
across the Big Holes and the Bear River Range could approach 2
ft accumulations by the time this event pushes through. Lower
end snow amounts above about 6000 ft remain sufficient to
support Winter Storm Warnings, and thus the watches have been
converted over.

Further northwest across the central mountains, most of the
region should be shadowed by northwest flow. Amounts above 6500
ft could be enough to support heavier snowfall, but that leaves
the only significant impact at Galena Summit with 6-10" (for
now). Held off on issuing an Advisory for now, but wouldn`t be
surprised to see locally higher accumulations early enough to
warrant an issuance.

The last complication is winds, which increase Friday into
Friday night with the onset of stronger winds aloft. At this
stage, do not believe the winds will reach Advisory level across
the Snake Plain, so will hold off on headlines for now. Gusts
late Friday into Friday night could produce some blowing snow
hazards in the warning area, so those gusts were mentioned in
the Winter Storm Warning as well.

Precipitation could continue into Saturday, again targeting
higher elevations especially across the east and south
highlands. This does look to be a relative "break" in the
pattern so total amounts look weaker than the previous 36 hours.
For now, will leave the ending of the current Winter Storm
Warning in place. Mild temperatures do remain at lower
elevations where precipitation looks to be much less, if at all.


&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Issued at 212 PM MST Thu Dec 4 2025

Confidence is high in above normal temperatures for much of the
extended period of the forecast. The greater forecast challenge lies
with respect to placement and timing of precipitation as the overall
pattern looks to remain messy with clouds and precipitation in place
despite the warmer than normal temperatures. Valley temperatures on
Sunday will be in the upper 30s to mid 40s but by Monday, should
climb into the mid to upper 40s. This upward trend continues into
Tuesday and towards the latter part of next week with upper 40s to
lower 50s appearing very likely despite all the cloud cover in
place. Mountain locations will also see above normal temperatures
but the warmup wont be as significant keeping temps in the upper 30s
to lower 40s for most days. This makes precip type challenging in
the extended with a messy snow/mix/rain forecast each day across
the higher elevations. As for precipitation, there is still large
spread amongst model guidance and their associated ensembles as to
where the heaviest precip will set up any given day with these
occasional surges of Pacific moisture moving in through the upper
level flow. Highest PoPs remain forecast across the higher terrain
of the central mountains and eastern highlands but valley locations
aren`t immune from the precip potential either. The spreads are
literally from no QPF to upwards of a quarter inch at times in the
lower valleys so it`s hard to have much confidence for any given
day. In short, expect above normal temps to remain in the forecast
with potentially wide variations from forecast to forecast on
precip locations, amounts and timing until better continuity against
within model guidance.



&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1100 AM MST Thu Dec 4 2025

BKN/OVC CIGs in the 1500-3500 ft range continue across eastern
Idaho terminals with the exception of KSUN which continues to be
on the far northern edge of some lower CIGs in the valley just
south of the airport. Expecting the upcoming TAF period to be
challenging with widespread low clouds and snow expected as our
next weather system moves through the region. KBYI, KPIH and
perhaps KSUN will likely see a transition from snow to a mix or
even all rain at some point while some warmer air moves into the
area from the south. Precip type confidence is lower than
desired but confidence is much higher with regards to prolonged
MVFR/IFR CIGs through much of the period. Winds will increase a
bit too during the period with 15-25 kt gusts possible in the
valley terminals.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 5 AM MST Saturday for IDZ058>066.

&&

$$

SHORT TERM...DMH
LONG TERM...McKaughan
AVIATION...McKaughan