273
FXUS65 KPIH 311937
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
137 PM MDT Sat Oct 31 2026

.KEY MESSAGES...

- Winter Weather Advisory starts 6 PM MDT today and goes through
  5 PM MST Sunday. Snow above 7000ft elevation in the Central
  Mountains.

- Moderate to heavy rain redevelops starting late tonight,
  continues into Sunday night.

- Cooling trend starting today, with warming returning to
  western areas Monday, other areas Tuesday.

&&

.DISCUSSION...
Issued at 1233 PM MDT Sat Oct 31 2026

There is currently moist, southwesterly flow aloft over
southern Idaho with light showers currently, mainly over our
the Central Mountains, western areas and the Island Park/Driggs
areas. Currently, there is an upper level low centered just off
the coasts of Washington and Oregon as part of an overall
trough that extends much farther south to off the coast of
California, where there is ample sub-tropical moisture
available. This low/trough is bringing our current moisture and
will drive the weather/precipitation today and Sunday,
especially as this low/trough moves over our area late today
into Sunday.

Precipitation for lower elevations today has dropped for the
Snake Plain, southeastern areas (Bear Lake Region), and northern
areas (Stanley and Challis) where a T to 0.04 is expected. The
Sun Valley Region and Island Park region will receive around
0.05 to 0.15 today. This precipitation will likely have some
impacts on Halloween activities. However, the bulk of the
precipitation is still arriving later this evening through
Sunday and lingering into Monday morning.

By late today into Sunday the low off the Washington coast
begins to move and makes it way inland aided by an deepening
trough, which will really picks up more Pacific moisture and
transports it over southeastern Idaho. This more organized round
of precipitation will begin in the Central Mountains/Wood River
Valley/eastern Magic Valley as early as 6 PM today and then
spread eastward throughout the night. The NBM model is still
showing about an 90 to 100 percent chance of the entire CWA
receiving at least 0.25 inch of precipitation with this system.
Precipitation amounts are up about 0.15 from yesterday`s model
round during day and down about 0.25 from last nights model
run. It still seems likely that many will see 0.20 to 0.50
inches in the eastern Magic Valley and Challis area, 0.50 to
0.80 inches in the Snake River Plain and lower elevations of the
Eastern Highlands and Central Mountains. For higher elevations
(above 8000 feet) precipitation will be pushing 0.80 to 1.25
inches, especially for Sun Valley Region, Big Lost
Highlands/Copper Basin, Lost River Range, and the Montana Divide
as well as the Southern areas along the Utah border including
the Wasatch mountains. Temperatures will still be slightly above
normal today with highs in the 40s and 50s, but by Sunday our
highs will drop into the mid and upper 30s and 40s. Snow impacts
are likely at Galena Summit today into Sunday morning with the
forecast still showing 3-7" of snow there. A winter weather
advisory is still in effect for the Sun Valley Region and the
Big Lost Highlands above 7000 feet for this evening through
Sunday. Elsewhere, the bulk of our snow is expected to remain
above most of the rest of our mountain passes, but that could
change easily with temperature changes of just a few degrees.
Even though snow levels will start high, convection can lower
snow levels, which could drop snow levels to pass levels
especially for areas like Emigration and Raynolds pass.

A few showers linger on Monday morning, but we will be drying
out from west to east by that point and high pressure builds in
on Monday. The breakdown of this upper level ridge is still in
question. There remain four different clusters of solutions in
this medium range period. It is about a 60-40 split that the
ridge will remain on Wednesday, then flatter, zonal flow or weak
troughing developing Thursday. Zonal flow makes timing of
shortwave energy more difficult, so there is quite a bit of
uncertainty in the forecast in the long-term.
&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1136 AM MDT Sat Oct 31 2026

East Idaho under the influence of wet low pressure system. Radar
shows rain showers moving through the region. Precipitation
timing for terminal forecasts heavily based on current radar
trends mixed with high-res model blend favoring the HRRR. CIGS
transition lower toward MVFR with occasional IFR overnight, then
to IFR around/after sunrise as rain becomes more widespread.
Other than an occasional shower induced gust 10-15kts, winds are
expected to remain light. SUN winds should remain terrain driven
as normal, but there is some question as to how much influence
the precipitation will have. There is some guidance suggestion
that the winds at SUN could turn south and remain south until
surface frontal passage mid-day Sunday, at which time winds
should become west or northwest.

&&

.FIRE WEATHER...
Issued at 200 AM MDT Sat Oct 31 2026

A low moving through the great basin, to Idaho`s south, will
bring rain and high elevation snow, with most of the wind on the
southern side of the low. Expect low temperatures through
Mon, high humidity through at least Tue, and some possible wind
in the southern Sawtooth NF on Sun.

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 5 PM MDT
Sunday for IDZ073-074.

&&

$$

DISCUSSION...TW
AVIATION...DMH
FIRE WEATHER...Messick