textproduct: Great Falls

KEY MESSAGES

- Snow will continue across the area through Monday morning.

- It will be significantly colder across the area on Sunday and Monday.

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

DISCUSSION

- Meteorological Overview:

Today there is an upper-level trough over Montana with multiple vort maxes. Through the day today it will continue to snow across North- central and Central Montana enhanced by tropical moisture from Tropical Storm Rachel. Today across Southwestern Montana in the mountains there will be snow and in the lower-elevations there will be a rain/snow mix. There remains uncertainty in how far south the colder air behind the cold front will make it. This will affect which lower-elevation areas see any snow during the day today. See the Forecast Confidence and Scenarios section for details. Today most areas of North-central, and Southwestern Montana will struggle to get above freezing. Sunday night snow-levels will lower across Southwestern Montana. This will bring primarily snow to all of the lower-elevations of Southwestern Montana Sunday night into Monday morning. Across North-central and Central Montana snow will continue Sunday night through Monday morning. On Monday the upper- level trough sinks further south. This will allow temperatures to warm up a little on Monday.

On Tuesday and Wednesday upper-level flow over Montana is weak. This will allow temperatures to warm up a few degrees each day. However they will remain below seasonal averages. On Thursday an upper-level trough briefly moves over Montana. This will slightly cool temperatures and bring precipitation chances to the area. On Friday and Saturday an upper-level ridge moves over North-central, Central, and Southwestern Montana. This warm temperatures and dry weather to the area on Friday. -IG

- Forecast Confidence & Scenarios:

For snow in the Southwestern Montana valleys, it will depend on how fast cold air makes it down there this morning. In addition with warm road temperatures most of the snow that falls in the Southwestern Montana valleys will melt through the day today. Additionally, snow accumulations at all lower-elevations of North- central, Central, and Southwestern will vary drastically from grassy/elevated surfaces to roadways due to warm road temperatures. The greatest impacts for any snowfall will be early this morning and Sunday night into early Monday morning. All snowfall will be wet and heavy. This means that it only will take a few inches of snow to cause power outages and/or break tree branches. The tree branches that are most susceptible to breaking are those that still have leaves. Currently the current Winter Weather Products are capturing the current situation well. The one exception is the Gallatin Valley. Most of the Hi-res guidance is predicting over 6 inches of snowfall with several inches of snow depth change in the Gallatin Valley Sunday evening into Monday morning. As a result the Gallatin Valley was upgraded to a Winter Storm Warning from 6 PM Sunday to 9 AM Monday.

Today across the North-central Montana plains along and east of I-15 there is a 30 - 70% chance for high temperatures of 36 degrees or colder. Tuesday morning across the North-central Montana plains along and east of I-15 and across the valleys of Southwestern Montana there is a 50 - 80% chance for temperatures of 20 degrees or colder. -IG

AVIATION

11/06Z TAF Period

The primary concern will continue to be for reduced cigs/vis from precipitation, mainly in the form of snow. Rain transitions to snow at most sites in SW MT through the day Sunday, though is likely to remain as rain at WYS through much of this TAF period. Precipitation more or less continues at most sites through the entire TAF period. Mountains will remain obscured this TAF period. -AM

PRELIMINARY POINT TEMPS/POPS

GTF 33 27 36 22 / 100 100 70 0 CTB 30 22 35 19 / 100 90 50 0 HLN 32 25 39 23 / 100 100 50 0 BZN 34 22 39 20 / 100 100 40 0 WYS 46 21 48 21 / 100 100 60 10 DLN 32 23 39 21 / 100 100 20 0 HVR 39 23 42 20 / 100 100 80 0 LWT 36 24 38 23 / 100 100 70 0

TFX WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 6 AM MDT Monday for Big Belt, Bridger and Castle Mountains-Cascade County below 5000ft-East Glacier Park Region-Eastern Pondera and Eastern Teton-Elkhorn and Boulder Mountains-Gates of the Mountains-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Meagher County Valleys-Northern High Plains-Snowy and Judith Mountains-Southern High Plains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory until 6 AM MDT Monday for Bears Paw Mountains and Southern Blaine-Beaverhead and Western Madison below 6000ft-Canyon Ferry Area-Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty-Fergus County below 4500ft-Gallatin and Madison County Mountains and Centennial Mountains-Helena Valley-Madison River Valley-Missouri Headwaters-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Western and Central Chouteau County.

Winter Weather Advisory until 6 PM MDT this evening for Gallatin Valley.

Winter Storm Warning from 6 PM this evening to 9 AM MDT Monday for Gallatin Valley.