textproduct: Great Falls

KEY MESSAGES

-Dense fog is possible this morning across the plains of North- Central Montana and the valleys of Southwestern Montana.

-Today it will remain significantly below seasonal averages with dry weather.

-Wednesday through Friday it will gradually warm up with mostly dry weather.

DISCUSSION

/Issued 154 AM MDT Tue Oct 13 2026/

- Meteorological Overview:

Today there is a weak upper-level ridge over North-central, Central, and Southwestern Montana. This will allow skies to clear. As a result of this combined with snow melting yesterday, fog is possible across portions of North-central, Central, and Southwestern Montana this morning. See the Forecast Confidence & Scenarios section for details. It will warm up a few degrees today across North-central, Central, and Southwestern Montana but still remains well-below seasonal averages. It will be dry today across the area. On Wednesday the weak upper-level ridge remains over North-central, Central, and Southwestern Montana. This allows the potential for there to be fog across North-central, Central, and Southwestern Montana tonight into Wednesday morning. See the Forecast Confidence & Scenarios section for details. On Wednesday temperatures will warm up some more but remain below seasonal averages. It will be dry across the area on Wednesday.

On Thursday an upper-level trough briefly moves over North-central, Central, and Southwestern Montana. On Thursday temperatures will be near seasonal averages with dry weather. On Friday and Saturday an upper-level ridge moves over North-central, Central, and Southwestern Montana. This brings warm temperatures and dry weather to the area on Friday and Saturday. On Friday and Saturday temperatures will be above seasonal averages. -IG

- Forecast Confidence & Scenarios:

There is a 60% chance for dense fog (visibility less than one half mile) in most areas of the plains of North-central Montana and most of the Central and Southwestern Montana valleys through this morning. From 12 PM to 6 PM today there is a 40 to 60% chance for dense fog (visibility less than one half mile) in the Gallatin and Helena Valleys. Tuesday night into Wednesday morning there is a 30 - 50% chance for fog in most valleys of Southwestern and Central Montana and across most of the plains of North-central Montana. The biggest area of uncertainty with fog this morning is if skies will clear and if winds will remain light. In areas that clear and have light winds dense fog will form. As a result across the plains of North-central Montana and most of the valleys of Central and Southwestern Montana a Dense Fog Advisory was issued through Noon today. For fog Tuesday night into Wednesday morning the biggest area of uncertainty is if snow will remain on grassy surfaces to enhance fog development. In areas that snow remains dense fog will have at least a moderate chance of forming Tuesday night into Wednesday morning due to calm winds and clear skies. -IG

AVIATION

13/12Z TAF Period

Fog will be the main concern this TAF period. Where it has formed (KBZN), it is dense, but has struggled to develop in most other areas. While time is running out for fog to develop this morning, the opportunity for it to develop will emerge once again this evening. The initial TAF issuance for this cycle shows some improvement to cigs/vis at KBZN later this morning, but there are some guidance members that suggest the fog may last all day there. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 43 23 50 33 / 0 0 0 0 CTB 45 22 52 30 / 0 0 0 0 HLN 43 22 49 31 / 0 0 0 0 BZN 39 18 45 25 / 0 0 0 0 WYS 46 14 50 18 / 10 0 0 0 DLN 38 18 45 25 / 0 0 0 0 HVR 45 20 53 29 / 0 0 0 0 LWT 40 22 49 31 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until noon MDT today for Bears Paw Mountains and Southern Blaine-Canyon Ferry Area-Cascade County below 5000ft-Eastern Glacier, Western Toole, and Central Pondera- Eastern Pondera and Eastern Teton-Eastern Toole and Liberty- Fergus County below 4500ft-Gallatin Valley-Helena Valley-Hill County-Judith Basin County and Judith Gap-Madison River Valley- Meagher County Valleys-Missouri Headwaters-Northern Blaine County-Western and Central Chouteau County.