Sun Valley

000
FXUS65 KPIH 312336
AFDPIH

Area Forecast Discussion
National Weather Service Pocatello ID
536 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 /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 528 PM MDT Sat Oct 31 2026

The main trend for this forecast is for VCSH to turn to showers
and eventually rain by early Sunday as precipitation increases 
over eastern Idaho. CIGs and VIS will also trend toward MVFR 
tonight with the potential for intermittent IFR heading into the
overnight/early morning hours Sunday as precipitation rates 
increase. Have maintained very similar timing to previous 
forecast. Winds are expected to remain light and variable for 
much of the period outside of any gusty showers.

&&

.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 until 5 PM MDT Sunday for IDZ073-074.

&&

$$

DISCUSSION...TW
AVIATION...Cropp
FIRE WEATHER...Messick