FXUS65 KPIH 011749

AFDPIH



Area Forecast Discussion

National Weather Service Pocatello ID

1049 AM MST Sun Nov 1 2026



.KEY MESSAGES...



- Winter Weather Advisory continues until this afternoon for

  portions of the central Idaho mountains.



- Moderate rainfall amounts expected into the evening hours,

  then tapering off overnight and Monday morning.



- Cooling trend in temperatures continues today and tonight,

  then warming trend in the west on Monday, nearly all areas 

  Tuesday.



&&



.DISCUSSION...

Issued at 147 AM MDT Sun Nov 1 2026



Today through Tue night...The upper level pattern has a trough 

to the north over western WA this morning and a closed low over 

northern CA, both in alignment longitudinally. By this 

afternoon, this pair will be at the WA-ID border in the north 

and over Las Vegas to the south. Weak upper level flow with 

abundant moisture as it gets close should develop from this, 

with moderate and locally heavy rainfall amounts, with snow 

above 7500ft elevation during the day. By midnight, this trough-

low pair has exited the Gem State and a north wind develops 

over the forecast area. This will shut off precipitation, save

for where the northerly to northwest surface wind can find an

upslope condition, such as in the eastern and southeastern

highlands.



Continued cloud cover will cool temperatures some more today

compared to Sat, then clearer skies in the west on Mon will

allow temperatures in the western areas to warm at least a

little. On the eastern side, temperatures will continue to cool

due to the cold air mass moving in due to the northerly wind. On

Tue, depending on fog formation, nearly all areas will see a

leveling off of the previous day's warming or a warming trend. 

Overnight lows plunge to the teens and 20s once the clouds are 

gone on Tue night, except in the eastern Magic Valley where they

should hover around freezing.



Moderate to strong wind possible in the wake of the trough,

especially in the mountains on Mon and to a lesser extent in the

Snake River plain tonight.



Wed through Sat...Even late Tue night the individual

deterministic model runs differ on the timing of the next

trough, with the NAM already developing precipitation at the end

of the short term period above. But most have it returning to

the highlands that border UT and WY on Wed. Only one cluster of

9 percent of the ensemble runs have no upper level troughing

over Idaho. The upper level zonal pattern keeps the forecast

highly uncertain in timeing for Thu and Fri, while Sat in all

clusters appears to be dry. However, changeability in the

foreast is highest here in autumn. One thing that can be said is

that there are no major upper level troughs making an approach

to the US northwest coast during this period.



&&



.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 12Z–14Z 

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 65–75% 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

25–30 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...Messick

AVIATION...DMH

FIRE WEATHER...Messick