textproduct: Great Falls

KEY MESSAGES

- Rain and snow showers will affect the area through Monday morning.

- It will be cold through Tuesday morning.

- It will gradually warm up Tuesday through the end of the work week with isolated showers around.

DISCUSSION

- Meteorological Overview:

This afternoon an upper-level trough associated with a surface Pacific Cold Front begins to move over North-central, Central, and Southwestern Montana. This will bring rain and snow showers and cooler temperatures to the area this afternoon. Ahead of the cold front in Southwestern Montana instability will build this afternoon. This will lead to a few rumbles of thunder across Southwestern Montana this afternoon. A Canadian Cold Front will move south from Canada tonight. On Sunday the upper-level trough remains over North- central, Central, and Southwestern Montana. This combined with the Canadian Cold Front will bring well-below seasonal averages for temperatures on Sunday. On Sunday there will be widespread precipitation across the area. Across mountain locations this will be snow. At lower-elevations this will be a rain/snow mix with some lower-elevation locations seeing all snow. Sunday afternoon there is enough instability around that there is the potential for a few rumbles of thunder as well.

On Monday the upper-level trough remains over North-central, Central, and Southwestern Montana. As a result precipitation and cold temperatures (well-below seasonal averages) will linger across the area. On Tuesday the upper-level trough remains over North- central, Central, and Southwestern Montana in the morning before an upper-level ridge builds over the area by the afternooon. This will keep cold temperatures across North-central, Central, and Southwestern Montana Tuesday morning before they gradually warm up by Tuesday afternoon. On Wednesday an upper- level trough builds back in over North-central, Central, and Southwestern Montana. This will bring isolated rain showers at lower-elevations and snow showers at mountain locations on Wednesday with about seasonal averages for temperatures. On Thursday and Friday an upper-level ridge builds in over North- central, Central, and Southwestern Montana. This will allow temperatures to warm up with mostly dry weather. -IG

- Forecast Confidence & Scenarios:

Sunday through Monday there is a 10 - 50% chance for greater than a tenth of an inch of snow across the lower-elevations of North- central, Central, and Southwestern Montana south of the Montana 200 Corridor. Across the mountains of North-central, Central, and Southwestern Montana there is a 50 - 80% chance for 4 inches of snow or greater. As a result Winter Weather Advisories have been issued for most of the mountain areas. An area of uncertainty is when the cold air moves in and transitions rain to snow or a rain/snow mix at lower-elevations. There is greater than a 25% chance for a quarter inch of liquid precipitation or greater across North-central, Central, and Southwestern Montana from this evening through Monday morning.

On Sunday morning across the lower-elevations of Southwestern Montana there is greater than a 50% chance for low temperatures of 28 degrees or colder. On Sunday across most of the lower-elevations of North-central, Central, and Southwestern Montana there is greater than a 50% chance for high temperatures of 45 degrees or colder. On Monday and Tuesday morning there is a 30 - 70% chance for low temperatures of 28 degrees or colder across the lower-elevations of North-central, Central, and Southwestern Montana. -IG

AVIATION

17/00Z TAF Period

Widespread rain/snow will affect much of the CWA through the period. Snow levels will gradually lower to plains/valley floors overnight. IFR or lower conditions should be planned for starting later this evening, and continuing through the day on Sunday. Surface winds will be breezy at times, with mountains/passes obscured throughout the period. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 31 40 27 52 / 30 80 40 10 CTB 30 38 25 55 / 50 70 10 0 HLN 32 43 30 54 / 30 70 30 10 BZN 28 45 28 49 / 90 30 30 20 WYS 23 37 21 43 / 50 20 20 10 DLN 25 45 23 50 / 40 40 20 0 HVR 35 44 29 53 / 50 80 50 10 LWT 30 39 27 45 / 90 70 60 40

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from midnight tonight to midnight MDT Sunday night for Big Belt, Bridger and Castle Mountains-East Glacier Park Region-Elkhorn and Boulder Mountains-Little Belt and Highwood Mountains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory until 6 AM MDT Sunday for Gallatin and Madison County Mountains and Centennial Mountains.