920
FXUS65 KPIH 012021
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
121 PM MST Sun Nov 1 2026

.KEY MESSAGES...

- Precipitation & Mountain Snow Tapering Tonight: Light-to-
  moderate rain will diminish areawide around midnight, while
  accumulating snow above 7,000 feet near Sun Valley winds down
  by early evening, allowing the high-elevation Winter Weather
  Advisory to expire on schedule.

- Overnight Patchy Fog Risk (Upper Snake Plain): Abundant
  boundary-layer moisture combined with lighter winds will
  support patchy fog and low stratus development across the
  Snake Plain tonight, focused particularly in the Upper Snake.
  Breezy winds in the Magic Valley should keep widespread fog at
  bay.

- Chilly Monday with West-to-East Clearing: Fall-like
  temperatures will linger on Monday, holding afternoon highs in
  the 40s to lower 50s as clouds steadily break from west to
  east.

- Predominantly Quiet Workweek & Eventual Warm-Up: Aside from
  weak, passing upper-level impulses that may spark low-end
  precipitation chances over mountain terrain, the upcoming week
  looks mostly dry, with ensemble guidance trending toward
  above-normal temperatures by next weekend.

&&

.DISCUSSION...
Issued at 117 PM MST Sun Nov 1 2026

A dreary Sunday continues across eastern Idaho, with afternoon
satellite imagery showing a broad cloud shield streaming
northward across the Great Basin. Regional radar shows light-to-
moderate rainfall persisting across the area, though high-
resolution convective-allowing models (CAMs) indicate
precipitation will steadily wind down around midnight. For the
higher terrain around Sun Valley, a Winter Weather Advisory
remains in effect for elevations above 7,000 feet, but CAMs
indicate snowfall will taper off by early this evening as
dynamic lift weakens and moisture pushes further east.

The primary operational concern overnight will shift to low
stratus and fog development given abundant low-level moisture
over saturated soils. Surface winds are forecast to remain
elevated across the Magic Valley, which should promote enough
mixing to keep fog largely at bay there. However, lighter winds
across the Snake Plainespecially the Upper Snakewill allow the
boundary layer to decouple and promote patchy fog development.
Patchy fog has been introduced into the forecast grids to
address this impact through early Monday morning.

Cool, fall-like conditions will linger to start the workweek. As
the departing disturbance pulls eastward, cloud cover will
gradually clear from west to east throughout the daytime hours
on Monday. Persistent cool advection and early morning cloud
cover will suppress diurnal heating, keeping daytime highs
capped in the 40s to lower 50s across the region. Not much
variation from one day to the next through the upcoming workweek
as far as temps are concerned. No major, high-impact storm
systems are on the horizon once today`s precipitation clears
out. Operational models depict a series of weak, transitory
upper-level impulses tracking across the northern tier, which
may spark low-end PoPs occasionally across the higher terrain,
but lower-elevation valleys look predominantly dry. Medium-range
ensembles continue to trend toward building heights and above-
normal temperatures late in the period and into the start of
next week. Given typical model spread at days 6 and 7, this
warming trend will be monitored in subsequent cycles as guidance
converges.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1049 AM MST Sun Nov 1 2026

Broad rain shield remains firmly anchored across east Idaho per
regional radar, satellite, and surface observations. While CIGS
currently show localized variability, expect prevalent MVFR to
dominate this afternoon through mid-evening across all
terminals, with periodic dips to IFR in heavier RA/BR. Precipitation
will begin tapering from northwest to southeast during the late
evening and early overnight hours for KSUN, KBYI, KPIH, and
KIDA. KDIJ remains the outlier, holding onto steady
precipitation and persistent low CIGs/VIS until roughly 12Z14Z
Monday morning.

Fog development becomes a primary forecast challenge overnight
as mid- and high-level clouds scatter out from the west over
rain-saturated surface. High-resolution ensemble guidance (REFS)
highlights a 6575% probability of visibility dropping below 3SM
between KPIH and KBYI after 09Z. Subsequent issuances may
require a prevailing or VCFG mention for both terminals
depending on clearing trends. However, surface winds behind the
passing front remain a significant complicating factor: gusts of
2530 kt across the Snake River Plain (KBYI, KPIH, KIDA) this
evening into tonight could mitigate fog formation and instead
favor redevelopment or reinforcement of MVFR stratus deck.

&&

.FIRE WEATHER...
Issued at 147 AM MDT Sun Nov 1 2026

Humidity remains high with a low moving through during the
evening hours today. Moderate to locally heavy rain is likely.
Wind is fairly weak save for the southern Sawtooth NF. A shift
to northerly air flow late tonight keeps temperatures cool,
especially once skies fully clear for Tue/Tue night. Wed through
Fri continue unsettled, with weak impulses moving through a
westerly flow that could trigger light showers and bring windy
conditions. By Saturday, upper level ridging develops over Idaho
as a more substantial low approaches the west coast.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST this afternoon for
IDZ073-074.

&&

$$

DISCUSSION...McKaughan
AVIATION...DMH
FIRE WEATHER...Messick