textproduct: Great Falls

KEY MESSAGES

- Wet snow and wind impacts through early this evening will diminish overnight.

- Greatest potential for moderate snowfall rates and windy conditions through early this evening across areas near the central Montana mountains

- Strong winds across portions of north-central MT diminish from west to east tonight.

- Drier but continued cooler than average conditions are expected for the weekend into early next week.

DISCUSSION

- Meteorological Overview:

A fairly vigorous mid level wave accompanied by anomalous moisture continues to lift north across central MT this afternoon ahead of an upper level trough tracking east across the Rockies. This will continue to support widespread precipitation across much of the area into early this evening before drying behind the eastward moving trough brings an end to precipitation from west to east late this evening/overnight.

Potential for embedded isolated thunderstorms and brief moderate- heavy precipitation rates will decrease late this afternoon as the strongest lift moves out of the area and stability increases. The risk for impacts from localized intense precipitation has also decreased as snow levels continue to lower, leading to reduced runoff.

Surge of colder air from Canada will continue to spread east across remaining eastern portions of north-central MT and south through the valleys of SW MT through the rest of this afternoon and evening, bringing a transition to wet snow to even the lowest elevations before precipitation ends later this evening. Strongest north/northwest winds with the initial surge of the cooler airmass across western portions of nort-central MT will begin to gradually decrease late this afternoon, while eastern portions of north-central MT will have winds peak late this afternoon but not likely to noticeably diminish until later tonight.

Moderate to heavy snowfall rates are most likely to occur late this afternoon with lingering anomalous moisture still in place ahead of the upper trough axis, with a transition to more orographic/up-slope forced snowfall occurring this evening before precipitation ends. High resolution model ensembles have the highest probabilities(80% or better) for 1"/hr rated across the Little Belt and N-central MT Island Ranges and nearby foothills between 4pm and 7pm with a 20-40% probability for adjacent portions of Fergus and Judith Basin counties including the Judith Gap and Lewistown areas.

A drier westerly flow moves across the Northern Rockies Saturday behind the departing system with a broad area of upper level troughing lingering across western Canada and extending to offshore of the US West Coast. This holds a cooler than average airmass across the region into early next week with surface high pressure centered over the Canadian Prairies and generally dry conditions prevailing through Monday. Medium range models are converging on the idea of a lobe of energy moving out of the larger scale trough across the NW US around Tuesday. This would be a colder system with lower snow levels to start, but would likely not have as much deep moisture available as the current system and there is still considerable uncertainty this this time with more specific details. Hoenisch

- Forecast Confidence & Scenarios:

Main concerns for winter weather impacts through the rest of this afternoon and evening are in areas that see the heavier snowfall rates in conjunction with windy conditions. This is most likely across areas near the Little Belts/Snowies and adjacent portions of Judith Basin, Fergus and southeastern Cascade counties. Hoenisch

AVIATION

23/18z TAF Period

Widespread rain/snow continues to fall this afternoon and into the evening across the region. The cold front will continue to usher in colder air, transitioning rain to snow at lower elevations this afternoon. Precipitation will continue to bring MVFR to LIFR conditions region wide. VLIFR conditions will be possible at times at KCTB and KLWT due to snow. Rain/snow exits between 23/23z to 24/05z. Along with precipitation, breezy to gusty northwest winds persists through the afternoon, decreasing in the evening. Wind gusts of 50kts will be possible at KCTB. -Wilson

PRELIMINARY POINT TEMPS/POPS

GTF 25 43 25 38 / 60 0 0 0 CTB 21 42 23 39 / 0 0 0 0 HLN 21 44 24 42 / 70 0 0 0 BZN 21 41 20 43 / 100 0 0 0 WYS 15 46 15 50 / 80 0 0 0 DLN 25 44 24 46 / 90 0 0 0 HVR 23 44 22 44 / 90 0 0 0 LWT 21 40 21 39 / 100 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 6 PM MDT this evening for Eastern Toole and Liberty-Hill County.

Winter Weather Advisory until 3 AM MDT Saturday for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Judith Basin County and Judith Gap-Snowy and Judith Mountains.

Winter Weather Advisory until 9 PM MDT this evening for Southern High Plains-Southern Rocky Mountain Front.

High Wind Warning until 9 PM MDT this evening for Fergus County below 4500ft.

Winter Weather Advisory until midnight MDT tonight for Big Belt, Bridger and Castle Mountains-Elkhorn and Boulder Mountains- Gallatin and Madison County Mountains and Centennial Mountains- Little Belt and Highwood Mountains-Northwest Beaverhead County- Ruby Mountains and Southern Beaverhead Mountains-Upper Blackfoot and MacDonald Pass.