textproduct: Great Falls

KEY MESSAGES

- There will be patchy dense morning fog for the next day or so, mostly over the southwest valleys and the Milk River Valley.

- Temperatures trend warmer each day, with 60s and 70s returning to most locations by the weekend.

- Gusty westerly winds develop along the Rocky Mountain Front and the plains on Saturday.

- Pacific weather systems look to bring cooler temperatures and periods of rain and snow next week.

DISCUSSION

/Issued 208 PM MDT Tue Oct 13 2026/

- Meteorological Overview:

A closed mid- level low will continue moving through the Great Basin and into the SW CONUS tonight into Wednesday. The CWA will generally be unaffected by this system aside from some spotty rain/snow showers along the MT/WY/ID borders through this evening. Otherwise, light winds and lingering surface moisture will favor some patchy fog redevelopment later tonight into Wednesday morning. The southwest wind protected valleys and the Milk River Valley will see the highest concentration of fog.

A trough and attendant frontal system looks to dive southeastward through the plains Wednesday into Thursday. This shouldn't exert much of a change to the sensible weather other than some gusty pre- frontal winds over the plains followed by a brief northerly wind shift.

Ridging aloft then develops during the second half of the workweek, which will bring a return to above average temperatures heading into the weekend. The ridge will be broken down by a broad trough that quickly passes through the Northern Rockies and brings gusty to localized strong winds to the Rocky Mountain Front and the plains Saturday into Sunday.

Nearly all ensemble suites highlight troughing settling over the western CONUS for much of next week; however, the individual members indicate the troughs will be undergoing shearing, which decreases forecast positioning and timing confidence. Overall, there's a general expectation of cooling temperatures and increased instances of rain and snow next week, especially for mountain areas. - RCG

- Forecast Confidence & Scenarios:

Patchy dense fog again tonight...

Light winds and lingering surface moisture will encourage patchy dense fog to develop again tonight into Wednesday morning. The latest HREF probabilities for visibility falling to less than a half mile are now running above 50% from Gallatin valley northward to Helena and then over the Milk River Valley. Confidence for impactful visibility reductions is highest in Bozeman/Belgrade and nearby areas given today's fog stubbornly lingering into the afternoon hours. A dense fog advisory has been issued for the Gallatin Valley and the neighboring Canyon Ferry and Missouri Headwaters zones. Will hold off on fog products for the Helena area and the Milk River Valley for now, but these areas will continue to be monitored heading into this evening. - RCG

AVIATION

13/18Z TAF Period

Fog will continue to be the main concern during the TAF period. Fog remains in place at KBZN, but does show signs that it will clear by 2100Z this afternoon. As for the rest of the region, no concerns through the rest of the day as conditions will be cooler and mild. Looking towards tonight, guidance members are favoring pockets of fog development after 0600Z. The period of time most favorable for fog development will be 0900-1500Z. There is at least a 50% chance of dense fog developing with visibility under 1/2 mile. Similar to last night and this morning, the main airports impacted will be BZN, WYS, and HVR. Currently, any areas of fog are expected to clear by 1500-1800Z tomorrow morning. For the rest of the region, cooler and mild conditions continue through the rest of the TAF period with no major concerns. -ESH

PREV DISCUSSION

/Issued 208 PM MDT Tue Oct 13 2026/

- Meteorological Overview:

A closed mid- level low will continue moving through the Great Basin and into the SW CONUS tonight into Wednesday. The CWA will generally be unaffected by this system aside from some spotty rain/snow showers along the MT/WY/ID borders through this evening. Otherwise, light winds and lingering surface moisture will favor some patchy fog redevelopment later tonight into Wednesday morning. The southwest wind protected valleys and the Milk River Valley will see the highest concentration of fog.

A trough and attendant frontal system looks to dive southeastward through the plains Wednesday into Thursday. This shouldn't exert much of a change to the sensible weather other than some gusty pre- frontal winds over the plains followed by a brief northerly wind shift.

Ridging aloft then develops during the second half of the workweek, which will bring a return to above average temperatures heading into the weekend. The ridge will be broken down by a broad trough that quickly passes through the Northern Rockies and brings gusty to localized strong winds to the Rocky Mountain Front and the plains Saturday into Sunday.

Nearly all ensemble suites highlight troughing settling over the western CONUS for much of next week; however, the individual members indicate the troughs will be undergoing shearing, which decreases forecast positioning and timing confidence. Overall, there's a general expectation of cooling temperatures and increased instances of rain and snow next week, especially for mountain areas. - RCG

- Forecast Confidence & Scenarios:

Patchy dense fog again tonight...

Light winds and lingering surface moisture will encourage patchy dense fog to develop again tonight into Wednesday morning. The latest HREF probabilities for visibility falling to less than a half mile are now running above 50% from Gallatin valley northward to Helena and then over the Milk River Valley. Confidence for impactful visibility reductions is highest in Bozeman/Belgrade and nearby areas given today's fog stubbornly lingering into the afternoon hours. A dense fog advisory has been issued for the Gallatin Valley and the neighboring Canyon Ferry and Missouri Headwaters zones. Will hold off on fog products for the Helena area and the Milk River Valley for now, but these areas will continue to be monitored heading into this evening. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 30 55 32 54 / 0 0 0 0 CTB 28 51 29 48 / 0 0 0 0 HLN 26 49 29 58 / 0 0 0 0 BZN 21 45 27 59 / 0 0 0 0 WYS 16 50 19 59 / 0 0 0 0 DLN 21 45 26 56 / 0 0 0 0 HVR 24 58 30 57 / 0 0 0 0 LWT 26 56 32 55 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory from 9 PM this evening to noon MDT Wednesday for Canyon Ferry Area-Gallatin Valley-Missouri Headwaters.