Area Forecast Discussion

KEY MESSAGES

- Periods of dense fog and even some isolated instances of freezing drizzle will continue over the next 24 hours, most widespread over central and north-central Montana.

- Precipitation becomes more widespread by Saturday night thru early Monday, with accumulating snow most prevalent over the higher terrain of southwest Montana.

- Below average temperatures trend closer to average next week.

DISCUSSION

/Issued 341 AM MDT Fri Oct 30 2026/

- Meteorological Overview:

Low level easterly flow will continue to bring low stratus and patchy fog for the next 24 to 36 hours, most widespread over central and north-central Montana. Meanwhile, a closed mid- level low churning over the Pacific NW will maintain a moist southwesterly flow aloft over the Northern Rockies and will send waves of spotty light precipitation over the forecast area, including isolated instances of freezing drizzle. The colder central/north-central areas and the high valleys along the MT/ID/WY borders will be most susceptible to trace amounts up to a few hundredths of an inch of ice accumulation.

The closed low will begin migrating towards the Northern Rockies Saturday night into Sunday. This system will be undergoing shearing and weakening, but will still bring a period of widespread precipitation Saturday night through early Monday. Most of the lower elevation precipitation will fall in liquid form Saturday night and most of Sunday, but there may be some lingering colder air for some light freezing drizzle, again mostly along the Hi-Line and the colder higher valleys of far southwest MT. H700 temperatures fall to around -5C by Sunday night and will bring more efficient accumulating snow over the higher terrain of the southwest. Colder northerly flow may also bring snow over the central island ranges, especially if a smaller scale vorticity max helps enhance the precipitation as some deterministic models are now highlighting.

Ensembles then favor ridging aloft to bring drier conditions and near average temperatures for much of the upcoming workweek. Westerly flow does increase some, but surface winds dont look to be much of a concern other than some breeziness along the Rocky Mountain Front and the nearby plains. - RCG

- Forecast Confidence & Scenarios:

..Periods of dense fog through at least Saturday morning

The cool and damp low level easterly flow will maintain nearly saturated surface conditions over central and north-central MT for the next 24 to 36 hours. The dense fog advisory was expanded to include the lower elevations of Judith Basin county and all of Fergus, with visibilities trending below the half mile mark. Conditions will marginally improve during the day today, but continued moist easterly flow looks to bring another round of fog tonight into Saturday morning. Most hires models highlight even more widespread fog than the previous couple of nights. Again central and north-central locations will see the worst conditions, but some southwest valleys also look to see more instances of fog tonight into Saturday morning. Impacts will mostly be directly related from the reduced visibility, but frost deposition and even some freezing drizzle may cause some slippery spots to develop on area roadways, particularly the more susceptible bridges and elevated surfaces.

Light mountain snow and lower elevation rain, snow, and some mixed precipitation Saturday night through Monday morning

The main trough moves through Saturday night through early Monday and brings widespread precipitation to much of the forecast area. The overall pattern and NBM probabilities favor the southwest mountains south of I90 for the best chance (60 to 80%) for snowfall amounts in excess of 3 inches. The higher terrain along the Continental Divide and the central island ranges will see some snow, but higher totals will be contingent on local vorticity maximums and northerly flow enhancing the precipitation, which is not looking to be fully aligned with the moisture. A thin cold layer may also encourage some spotty freezing drizzle to develop along the Hi-Line and over some of the higher valleys along the MT/ID/WY borders Saturday night into Sunday morning, but impacts appear to be limited at this time. - RCG

AVIATION

30/12Z TAF Period

Moist easterly flow in the low levels will maintain IFR/LIFR stratus and patchy/areas of dense fog for much of the period, although there will be notable improvement between 30/18 and 31/04Z. Central and north-central areas north of the central island ranges will be most susceptible to the degraded flight categories and mountain obscuration; however, instances of low stratus and fog will become more common over the southwest valleys after 31/06Z. - RCG

PRELIMINARY POINT TEMPS/POPS

TFX WATCHES / WARNINGS / ADVISORIES

Dense Fog Advisory until noon MDT today for Cascade County below 5000ft-Eastern Glacier, Western Toole, and Central Pondera- Eastern Pondera and Eastern Teton-Fergus County below 4500ft- Gates of the Mountains-Judith Basin County and Judith Gap- Northern High Plains-Snowy and Judith Mountains-Southern High Plains.