textproduct: Great Falls

KEY MESSAGES

- Dry this afternoon with breezy winds decreasing this evening.

- Potential for dense fog along the Hi Line tonight and Sunday morning.

- Temperatures drop back towards average next week, with a few rounds of light mountain snow and lower elevation rain.

UPDATE

/Issued 830 PM MST Sat Nov 15 2025/

Tonight there will be fog along the Hi-line east of Joplin. Otherwise it will be a mild and dry night across North-central, Central, and Southwestern Montana. There remains greater than a 40% chance for fog with visibility of a half mile or less along the Hi-Line east of Joplin. Given there remains uncertainty in how dense and widespread the fog will be a Dense Fog Advisory was not issued at this time. It will be monitored through tomorrow morning to see if an advisory is needed. The forecast is on track. -IG

DISCUSSION

/Issued 830 PM MST Sat Nov 15 2025/

- Meteorological Overview:

Slight ridging moving in this afternoon has helped pushed out morning precipitation. Mid level winds decreasing this afternoon and evening will decrease the breezy winds mixing down along the stationary front this afternoon after peak heating. The main concern overnight tonight is relative humidities raising near or at 100% and light winds along the Hi-line/northern Chouteau County will produce freezing fog. Although a broken low stratus deck will set up along the Milk River Valley tonight, high relative humidities already this afternoon gives some concern of fog developing tonight despite cloud cover. Hi-res guidance gives a 40-80% chance for visibility down to a half mile or less in this region. Therefore, there's a good chance for dense fog if fog develops, and a Dense Fog Advisory may be needed later tonight if it materializes widespread. Areas that get dense freezing fog may develop icy spots on pavements and cause hazardous driving conditions.

A closed wave in the Great Basin region moving northwest early this week will bring the next chances for precipitation. However, this closed wave is forecasted to weaken and "open up" as it reaches the Interior Mountain West. Weakening forcing aloft combined with warmer temperatures aloft will keep precipitation and mountain snow light overall. Behind this, another splitting trough looks to move through late Tuesday/Wednesday, but differences in positioning gives some uncertainty of how much precipitation falls. Another trough looks to form along the Western U.S. towards the end of next week. Since the the main core of this trough looks stays off to the south, I am not too concerned of any major impacts at this time.

- Forecast Confidence & Scenarios:

Slight differences in the evolution in this weakening wave and weak troughing the beginning of the week still gives a broader range of precipitation amounts. The 25th percentile of the NBM gives lower elevations up to 0.05" of precipitation Monday- Wednesday, 0.15-0.20" in the Southwest MT and 0.25-0.3" along the Northern Continental Divide. The 75th percentile NBM gives lower elevations 0.15-0.30" of precipitation, 0.60-0.75" in the Southwest MT and 0.60-0.80" along the Northern Continental Divide. Even if the higher precipitation amounts accumulate, snow in the mountains will stay minor. There's a 20-40% chance for 3" of snow in the mountains during this time period, with most impacts staying above pass level. -Wilson

AVIATION

16/06Z TAF Period

VFR conditions will prevail across all terminals during this TAF Period except for at the KHVR terminal. At the KHVR terminal between 16/08Z and 16/14Z there will be fog that reduces visibility to a quarter mile or less. At the KHVR terminal between now and 16/08Z there will be fog around the terminal with visibility intermittently dipping down to LIFR levels. Across all the terminals winds will be light during this TAF Period with mid- level clouds around (excluding the KHVR terminal).-IG

The KWYS TAF will not be issued until airport operations resume next spring.

PRELIMINARY POINT TEMPS/POPS

GTF 35 56 40 55 / 0 0 10 30 CTB 29 50 34 54 / 0 0 10 10 HLN 35 55 38 53 / 0 10 20 50 BZN 32 57 36 52 / 0 10 20 50 WYS 26 48 30 40 / 0 50 70 80 DLN 33 56 35 50 / 0 10 20 40 HVR 27 49 34 50 / 0 0 10 30 LWT 33 58 37 53 / 0 0 10 30

TFX WATCHES/WARNINGS/ADVISORIES

None.