textproduct: Great Falls

KEY MESSAGES

- Patchy dense fog continues this afternoon and is likely to expand in area tonight; potentially another round Friday night.

- Seasonable afternoon temperatures the next few days, with the potential for warmer afternoon temperatures by later next week.

- A good chance for widespread rain and snow Saturday night into Sunday over much of the region.

UPDATE

/Issued 713 PM MDT Thu Oct 29 2026/

This evening into Friday morning there will be fog along and west of the I-15 corridor between Cascade and the Canadian border. For the update, minimum temperatures across North-central Montana were decreased and the hourly temperatures were regenerated. Also the fog coverage along and west of the I-15 corridor between Cascade and the Canadian border was increased. The rest of the forecast is on track. -IG

DISCUSSION

/Issued 713 PM MDT Thu Oct 29 2026/

Today...

Areas of fog and low clouds persist across much of the north- central MT plains, where a very moist low level airmass is in place on the southwestern fridge of surface high pressure centered across the Canadian Prairies. Light low level easterly upslope flow is supporting some of the most widespread/dense fog affecting areas adjacent to the Rocky Mountain Front and Cascade county. A Dense Fog Advisory continues through 21z adjacent to the Rocky Mtn Front.

Tonight through Friday night...

Surface high pressure currently centered across southern AB/SK slowly slides eastward through Friday night and is likely to hold the shallow/moist airmass in place across the the plains, maintaining at least some areas of low clouds and fog across portions of north-central MT. Dense fog advisories will likely be needed again tonight through Friday morning for many of the same locations experiencing fog today. Latest high resolution model ensembles give a 60% probability for visibility 1/2 mile or less for areas of north-central MT along and west of I-15. Additionally, overnight temperatures near or slightly below freezing will support freezing fog again tonight as well, and even the potential for some patchy freezing drizzle with the risk for localized icing, particularly affecting bridges and overpasses.

This weekend... An upper level low over the Pacific Northwest will dig southeast towards Utah into Saturday. This will result in a moist southerly flow aloft to developing over Central MT. As a result, rain/snow is forecast to develop Saturday night over Southwest MT and then move into Central MT by Sunday morning. Latest model guidance continues to support widespread precipitation development Saturday night into Sunday with precipitation exiting the area Sunday night or Monday morning. This storm system will bring rain/snow to much of the CWA. Snow levels will be high to start, generally above 7000 feet on Saturday, but then are forecast to fall down to about 4000 feet Monday. By Monday, most of the precipitation will have exited the region, but mountain snowfall is likely Saturday night into Sunday. Snow accumulations around the Pony/Big Sky area are starting to approach warning criteria. Thus a winter storm watch might be needed for Zone 330. Otherwise, a winter weather advisory is looking likely for mountain areas of Southwest and portions of Central MT from Saturday night into Sunday night.

As the next upper level ridge starts to build over the northern Rockies. The main question is how strong will it be. Overall, we expect drier and slightly warmer conditions by the later portions of next week as this upper level expands. Afternoon temperatures might be a bit warmer than currently forecast for the later half of next week. Hoenisch/Brusda/WMR

AVIATION

30/06Z TAF Period

VFR conditions will prevail at all terminals except for the KCTB, KGTF, KLWT, and KHVR terminals during this TAF Period. Fog will affect the KGTF and KCTB terminals through at least 30/17Z. This fog will become dense after 30/09Z and reduce visibility to at least one half mile through at least 30/16Z. Through at least 30/16Z there will be LIFR-level ceilings at the KCTB and KGTF terminals with LIFR- level cielings continuing through the end of the TAF Period at the KCTB terminal. At the KHVR and KLWT terminals during a portion of this TAF Period there will be at least IFR-level ceilings. Across North-central Montana there will be periods of mountain obscuration during the majority of this TAF Period. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 28 39 30 52 / 10 0 10 0 CTB 25 36 26 50 / 30 10 10 0 HLN 28 45 31 50 / 0 0 20 0 BZN 27 48 30 48 / 0 0 10 30 WYS 23 52 26 45 / 0 0 50 70 DLN 30 50 33 48 / 0 10 20 30 HVR 27 46 26 50 / 0 0 0 0 LWT 25 47 29 53 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until noon MDT Friday for Cascade County below 5000ft-Eastern Glacier, Western Toole, and Central Pondera- Eastern Pondera and Eastern Teton-Gates of the Mountains- Northern High Plains-Southern High Plains.