554
FXUS65 KPIH 010954
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
254 AM MST Mon Dec 1 2025

.KEY MESSAGES...

- Light snow moving in tonight and continuing light into Tuesday
  evening. Heaviest in the Island Park/Fremont County region.

- Temperatures staying below 40 degrees for most, 45 for the
  eastern Magic Valley, lower elevations in the southern hills
  and the lower Wood River drainage.

- Next winter storm arrives Friday and continues through Friday
  night, bringing mountain snow, low elevation rain and snow.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 224 AM MST Mon Dec 1 2025

Some light precipitation may come out of the stratus layer that
has spread out everywhere except the Burley /I-84 area, mainly
hovering around 1000 to 2500 ft above the Snake River plain, so
this may mean fog at elevations of 5500ft to 6500ft where the
stratus impinges on the terrain. Have kept the freezing fog that
previous shift put in for today. The wind is finally subsiding
but still many locations exceeding 10 mph, mainly in the Snake
River plain.

Locations in the north will start to receive snow first during
the early evening, spreading southward before midnight.
Accumulations are slightly heavier in the northeast corner than
previous thinking, but average snow accumation for any forecast
zone is averaging less than 6 inches in the mountains, and less
than 3 inches in the Snake River plain, so see no need for any
formal highlights to the forecast (Watch/Warning/Advisory).

Temperatures appear to unsteadily rise and fall with the
approach of this trough and the next one on Friday. Afternoon
highs are slightly higher for most locations on Tuesday, then
warmer for everyone from Tuesday to Wednesday. However, still
staying colder than 46 degrees everywhere on Wed, and for most
below 40 degrees, such as the Interstate 15 corridor. Tue night
should be the coldest night of this period, between winter
storms.

Wind will continue to weaken during the day today, but increase
again tonight and peak during the day on Tuesday. Tuesday night
has a northerly component to the wind, which accounts for the
cold temperatures, in the teens for most, on that night. The
air flow shifts back to southwest during Wed afternoon, allowing
temperatures to warm again.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Issued at 224 AM MST Mon Dec 1 2025

The main storm for this period should arrive on Fri or Sat.
Cluster analysis was not available save for a consensus that
Thu should be dry with positive 500mb height anomalies for the
Gem State. Based on deterministic forecasts available, there is
a risk every period except Thu and Thu night. However, the
temperatures are warmer, with freeze-thaw occurring in the Snake
River plain. Wind looks potentially very strong with this Fri-
Sat storm, especially Sat morning. May need Wind Advisory for
this event and Winter Weather Advisory/Winter Storm Warning for
the Sawtooth zone and the eastern mountains south of Driggs to
the Utah border.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1100 PM MST Sun Nov 30 2025

Forecast generally remains on track along the lines of the thinking
below in the previous discussion...have issued several amendments
this evening to capture low stratus trends and tweak impact timing.
The earlier low stratus shield over KBYI and KPIH remained much more
intact than models indicated and advected all the way into KIDA a
bit early, while we are also now seeing redevelopment to the west of
this batch over the Shoshone region on satellite...the "main"
overnight event beginning. Also in line with earlier thinking...no
signs of fog so far, although still hard to rule it out. The NBM is
trending more pessimistic than most other guidance on dissipating
the stratus shield over KIDA tomorrow afternoon...for now have
nudged to 20z/1pm for a return to VFR conditions. Finally, noted
significant timing and coverage differences on the 00z HREF suite
with regard to snow shower activity moving in Monday evening with
the next disturbance...at this time have nudged VCSH timing up to
02z/7pm at KSUN but do not yet have confidence to introduce any
impacts at the other TAF terminals, with any snow shower potential
likely holding off until close to the end of the current TAF period.
Will continue to evaluate. Previous discussion is below.

Issued at 455 PM MST Sun Nov 30 2025

We have some fresh aviation challenges to discuss for tonight. The
HRRR, NBM, and HREF...with some hints in MOS guidance...continue to
support an organized round of low stratus and fog developing
overnight from the eastern Magic Valley and Shoshone lava beds
northeast across the Arco Desert into portions of the upper Snake
Plain...and we have no strong reasons to discount this scenario.
Based on projected surface RH values...low stratus may be slightly
favored over fog...but neither can be completely ruled out at this
time. KBYI and KPIH will likely reside near the southern edge of
this zone. Most guidance supports current low stratus over KBYI
breaking up this evening, so have held with only SCT coverage
overnight there with the main event redeveloping to the north
(although there is perhaps a 20% chance of IFR conditions making it
south into KBYI). However, the current low stratus shield is
currently advecting northeast into KPIH with strong SW winds, and
confidence is very low in this breaking up or dissipating before we
see the round of overnight development on their doorstep, so have
leaned MVFR BKN here with a 30% chance of seeing IFR conditions.
KIDA continues to have the highest potential in seeing significant
impacts, with guidance supporting IFR to possibly LIFR cigs and
vsbys. For now in the forecast...have leaned into the stratus and
away from the fog just a touch (but low confidence in this),
advertising borderline LIFR cigs from 09-17z/2-10am with decent
consensus among our models on this timing. This stratus may get
close to KDIJ on the northeastern fringes, but with very low
confidence there, have only hinted with SCT015 for now. Models bring
the low stratus shield VERY close to KSUN, but with MOS and NBM
guidance strongly supporting their usual diurnal wind cycle, think
downslope/downvalley flow/drying from the northwest will keep RHs a
bit lower and hold the stratus to the south of the terminal. See
TAFs for exact current timing for each terminal. All sites return to
VFR by midday Monday with clouds generally breaking up and yet
another brief break between systems, before clouds start to increase
again Monday evening ahead of our next disturbance. VCSH has been
introduced at KSUN after 03z/8pm Monday night, with snow showers
eventually likely across the region by Tuesday morning beyond the
current forecast period. We may be able to initiate some impacts at
KSUN and KBYI with the next set of TAFs at 06z after a review of the
fresh HREF CAMs suite.

&&

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

&&

$$

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