textproduct: Pocatello

KEY MESSAGES

- Fog and low clouds will continue to affect some areas through Tuesday, especially during the overnight and morning periods, amid a continued quiet weather pattern for the region.

- A pattern shift is then expected later this week, with potential for (finally) some rain and snow after Wednesday, especially in mountain areas.

UPDATE

Issued at 620 PM MST Sun Jan 18 2026

Idaho Transportation Department weather stations are showing some very dense fog is out there, so have issued a Dense Fog Advisory. The fog bank is currently into the American Falls area and continues to propagate eastward, so have included the lower Snake River plain, besides the eastern Magic Valley.

SHORT TERM /THROUGH TUESDAY/

Issued at 1244 PM MST Sun Jan 18 2026

Fog and stratus continues to be an issue across the Magic Valley. Based on the latest forecast, we will likely see it hanging around in some form into this evening. At that point, we expect it to expand and make a run up into the Snake Plain and surrounding adjacent valleys. We MAY see some pockets in other valleys across the area, but not as widespread as across the Plain. We expect to thin out a bit tomorrow afternoon, but likely not 100% gone before redeveloping tomorrow night and Tuesday morning. Coverage will likely extend up to the Montana border tomorrow night, along with some potential in other valleys. The question will be the extent of any dense fog. We did let the one from this morning expire, but fog is still there and locally dense especially back toward Twin Falls and Jerome. We wouldn't be shocked if another advisory is needed for tonight and tomorrow, and again tomorrow night and Tuesday. Believe it or not, the stratus deck along with a "wave" dropping along the Divide may kick off some flurries later Tuesday around Island Park. It isn't a slam dunk but something different in the forecast. Temperatures will remain in the 20s and 30s where inversion and lingering fog/stratus hold temperatures down, otherwise we will see some lower 40s around. That said, the trend is overall slightly cooler than past days.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

Issued at 1244 PM MST Sun Jan 18 2026

We are still looking at a pattern change, BUT it appears to more of another shift in where the low/high pattern sets up. The ridge breaks down, but now very briefly and ends up reestablishing itself farther out in the Pacific. There is a closed low still expected to drop into the southwest U.S. As this happens, we still active weather with the overall low pressure pattern over the northern U.S. shifting west. There is some moisture embedded within the pattern, so precipitation eventually returns, likely later Thursday or Friday now. It still looks like the mountains will see most of what falls, but with the flow now remaining more northerly...that means moisture will be much less than when it looked like we might get more a direct shot from the Pacific. Any moisture we see is likely not going to put any dent into our lack of precipitation issues of late, especially at lower elevations. Temperatures do warm up just a bit later in the week, but that is likely due just losing the ridge and some mixing takes place.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1025 PM MST Sun Jan 18 2026

Several amendments have been necessary this evening to speed up the forward progress of the fog/low stratus bank northeast up the Snake Plain as we watch webcams and satellite trends (now expected to reach KIDA around 08z/1am) and nudge cigs/vsbys even lower at KPIH where impacts also arrived several hours earlier than expected. We also added a Dense Fog Advisory covering KBYI and KPIH. KBYI, KPIH, and KIDA will remain in LIFR and near or below airfield minimums through 17-18z/10-11am Monday. No other major changes were needed with the 06z TAF package. Still moderate confidence on when impacts will end Monday...don't think it will be earlier than currently advertised in the forecast, with perhaps some hints in the NBM and HRRR that it could be an hour or two later for some spots. We'll be watching this with future updates. Previous discussion is below.

Issued at 450 PM MST Sun Jan 18 2026

Despite such a quiet weather pattern for most areas, THE MOIST is coming. Swath of entrenched LIFR moisture manifesting as both dense fog and low stratus remains very clearly visible on satellite down the Treasure Valley into the eastern Magic Valley. Models overestimated how much erosion would occur this afternoon and how cold sfc temps would stay in that area, and the swath is already expanding northeast on the satellite loop with a very light up- valley/up-plain sfc flow now observed on many weather stations. Even with models starting out too optimistic as of the issuance time of this discussion, strong agreement exists between the NBM and HRRR in advecting this moisture northeast up the Snake Plain tonight, posing major impacts for several of our terminals.

Our TAF for KBYI now carries LIFR conditions below airfield minimums from now straight through to 18z/11am Monday due to fog/low stratus, and our neighboring office out of Boise has just issued a Dense Fog Advisory through the same time covering the nearby terminals of KTWF, KJER, and KGNG. Confidence in impacts is highest in this Magic Valley region, with those impacts already occurring and expected to slightly worsen as the sun sets and things cool further this evening. Further northeast up the Snake Plain, confidence is growing in the fog/low stratus deck reaching KPIH between 07-09z/12-2am tonight, which will quickly send them into LIFR and very close to airfield minimums from 09-17z/2-10am. Confidence in onset timing is moderate to high, but a bit lower for exactly when things will dissipate Monday, although overall model agreement so far is decent on that end too. We will need to watch upstream trends this evening to see if cigs/vsbys need to be lowered even further at KPIH. Confidence is lowest in the action reaching up to KIDA, but both the NBM and HRRR do support it just barely reaching the terminal, and nearly all model VWPs as well as HRRR guidance lightly switch (mostly variable) sfc winds into the SW late tonight which would assist in the advection as well (whereas a light flow out of the north holding on longer would keep drier air in place). Thus, we now forecast KIDA to reach LIFR and approach airfield minimums as well starting around 11z/4am, lasting until around 17z/10am. Meanwhile, VFR conditions will reign at KSUN (normal diurnal wind cycle with light speeds) and at KDIJ, with guidance keeping cig/vsby impacts out of those two terminals. We may be contending with yet another round of fog/low stratus Monday night/Tuesday as well, at least at KBYI and KPIH.

AIR QUALITY

Issued at 1244 PM MST Sun Jan 18 2026

We have extended the AIR STAGNATION ADVISORY out through Tuesday for now. We really haven't seen any movement of poor air across the Pocatello area as well as across the Cache Valley, even with the flow more northerly and no longer directly under the ridge. This pattern should hold through Tuesday. We do see the pattern change, or more of a shift farther west again, by midweek. The issue that we will see increase in wind and precipitation, but moisture potential is lower than before and the pattern shift may not be strong or different enough to completely scour things out especially down near the Utah border. Stay tuned.

PIH WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until noon MST Monday for IDZ051-054-055. Air Stagnation Advisory until noon MST Tuesday for IDZ054-059.