textproduct: Great Falls

KEY MESSAGES

- Fog will continue to clear out during the afternoon.

- A storm system will bring light mountain snow and light rain/snow at lower elevations late tonight into Tuesday morning.

- Cooler and an slightly unsettled weather pattern continues through the rest of the week.

DISCUSSION

- Meteorological Overview:

Current satellite trends show fog and lower clouds are lifting out of Southwest MT as warmer air mixes down to the surface. Across North-Central MT, patchy dense fog has lifted but lower clouds have been slower to dissipate.

An upper-level trough bringing a low pressure system moves into the region later today, bringing precipitation from the southwest to the north. Warm air advection ahead of the system will bring rain initially, but a cold front will lower snow levels, transitioning to light snow in the mountains. Snow levels do fall towards 4,000ft to 4,500ft Tuesday morning, bringing a light rain to snow mix at lower elevations.

Throughout the week, multiple quick hitting troughs move through the northwest, keeping daily chances for precipitation through the rest of the week and into the beginning of next week. Precipitation will be mainly in the mountains/passes with light snow, especially along the northern Continental Divide. Isolated rain/snow will be possible at lower elevations at times throughout the week. Cooler temperatures remain through the forecast period due to the consistent troughing pattern.

- Forecast Confidence & Scenarios:

Dense fog and lower clouds are lifting out of Southwest MT this afternoon as the warm front approaches. Therefore, I will allow the dense fog advisory to expire at 3pm. Any lingering fog this afternoon will become mixed out later in the day as the incoming system approaches.

Messaging remains consistent with this incoming system today into Tuesday. There's a 30% chance for 3" of snow or greater above ~6,000ft in Southwest MT and Marias Pass, keeping minor impacts for snow at pass and above pass level. Additional accumulations later this week look to remain light, with Marias Pass at a 30% chance again for 3" of snow on Wednesday. Wet bulb temperatures struggle to reach 32 degrees across lower elevations except for the higher Southwest MT Valleys, therefore any snow that does fall all lower elevations will struggle to accumulate. -Wilson

AVIATION

26/18Z TAF Period

The primary concern this afternoon will be IFR/LIFR stratus and patchy fog lingering through at least 26/21Z, with slow improvement from there. Then a mid- level closed will will bring degraded conditions ranging from low VFR to IFR tonight into early Tuesday. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 32 50 36 50 / 60 10 0 0 CTB 26 46 29 43 / 30 40 0 0 HLN 32 49 26 49 / 80 10 0 10 BZN 30 47 25 47 / 90 10 0 0 WYS 20 37 17 38 / 100 40 20 10 DLN 28 44 24 44 / 80 0 0 0 HVR 29 49 30 49 / 40 70 30 0 LWT 32 48 30 49 / 70 50 0 0

TFX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 3 PM MDT this afternoon for Elkhorn and Boulder Mountains-Gallatin Valley-Madison River Valley-Missouri Headwaters.

Winter Weather Advisory from 9 PM this evening to 6 AM MDT Tuesday for Gallatin and Madison County Mountains and Centennial Mountains.