240
FXUS65 KPIH 010331
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
831 PM MST Sun Nov 30 2025

.KEY MESSAGES...

- Some combination of low stratus and fog across portions of the
  eastern Magic Valley, Shoshone lava beds, Arco Desert, and
  Upper Snake Plain to bring aviation impacts to some terminals
  including especially Idaho Falls tonight into Monday morning.

- Much colder temperatures remain in place this week with
  another round of snow likely on Tuesday.

&&

.UPDATE...
Issued at 829 PM MST Sun Nov 30 2025

This evening`s HRRR shows better fog potential out across the
Arco Desert into the upper Snake Plain later tonight, in an
area that is mostly clear this evening. Updated forecast to
mention patchy freezing fog for that area for the rest of the
night into Monday morning.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 112 PM MST Sun Nov 30 2025

The upper level shortwave that brought some light snow to parts
of eastern Idaho this morning is already moving into Utah.
Afternoon satellite imagery shows that in its wake, skies are
clearing across much of the area although some low clouds linger
across the south hills and into the Magic Valley. These are the
areas that saw the most of the early morning snow today with
very light accumulations. The snow is mostly over at this point
aside from maybe a few lingering snow showers, with limited
impacts and accumulation, across the far SE portion of the state
around Bear Lake. Models are showing the potential for some fog
overnight tonight but this is likely a bit overdone as not
nearly as much snowfall fall across the region as was advertised
so they`re likely seeing extra moisture in the lower levels
that isn`t actually there. As such, trimmed back the mention of
fog tonight to areas that actually saw light snowfall this
morning but confidence in this is still quite low. Upper flow
tonight remains out of the north and will through the day
tomorrow keeping temperatures cold with overnight lows generally
in the teens with some single digits in the normally colder
mountains locations. HIghs tomorrow will mainly be in the 30s
again throughout the region with things expected to stay dry
until we move into the late evening hours on Monday and into
Tuesday when our next shot at widespread snowfall is expected.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 112 PM MST Sun Nov 30 2025

The next shortwave feature drives south through East Idaho
during the day on Tuesday, focusing precipitation over the
eastern and southern highlands. There is quite a bit of spread
in precipitation amounts for the region, with the deterministic
NBM shading toward the higher end of the probabilistic range.
That said, in general the liquid amounts remain light, so snow
accumulations are expected to remain around or below an inch at
best in the Snake Plain along the I-15 corridor. Higher
elevations generally range 2-4" through Tuesday night. The
shortwave sags south of the state Wednesday, with dry northerly
conditions for most of the region Wednesday. For Thursday
through Sunday, the ensemble clusters remain out of agreement.
The ECMWF and derivatives trend toward rebuilding a ridge across
the coastal states while the GFS and derivatives develop a fast
and wet zonal flow across the eastern Pacific. NBM means
continue to trend toward near to slightly above normal
temperatures and unsettled conditions.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
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.

&&

$$

UPDATE...13
SHORT TERM...McKaughan
LONG TERM...DMH
AVIATION...01