textproduct: Great Falls

KEY MESSAGES

- Bitter cold expected across portions of Central and North- Central Montana through Thursday morning.

- Another round of snow expected across Central and Southwest Montana with the greatest impacts expected south of the I-90 corridor.

- Temperatures start to moderate back towards seasonal normals by the weekend.

DISCUSSION

- Meteorological Overview:

Another shortwave will push through today and bring another chance for snowfall across southwest Montana. While snowfall amounts are generally expected to be light there is a concern for some locally higher amounts. Otherwise the main concern in the short-term will be dangerous wind chills across portions of central and north- central Montana with widespread wind chill temperatures as low as 30 below expected.

Towards the weekend, upper level ridging starts to build over the Intermountain West allowing for temperatures to moderate back towards seasonal normals. While there is still a bit of uncertainty for the upcoming week, there are hints in the models that warmer weather may return to Montana sometime next week.

- Forecast Confidence & Scenarios:

Snowfall Today:

Light snowfall is expected across central and southwest Montana through Thursday morning. Some periods of heavier snowfall are possible, especially across southwest Montana with a concern for impacts along the I-90 corridor. Given the higher snowfall amounts and impacts expected, a Winter Weather Advisory was issued through late Wednesday.

All that considered, there are two wild cards for today. The first is the potential for snowbanding in the West Yellowstone area which could produce some localized enhanced snowfall that impacts the town of West Yellowstone as well as the surrounding passes. Right now, looking at potential impacts and snowfall amounts, there is not enough confidence to justify anything higher than a warning but folks traveling through the area should be prepared for sudden reductions in visibility and road conditions through the afternoon hours.

The second wild card is potentially locally enhanced snowfall in Bozeman. Slight changes in how this system moves through could make a big difference but if blocked flow sets up, Bozeman proper could end up seeing higher amounts than currently forecasted. Because there is varying confidence in whether this will play out, for now an advisory will suffice. But this situation will be monitored closely in case additional impacts start to appear.

North of I-90 there is a chance for light snow through the day on Wednesday. However, snowfall amounts do not look terribly impressive at the moment and there is much lower confidence going north. Thus these regions were left out of the Winter Weather Advisory. But should the track of the low shift a little further north, this situation will need to be re-evaluated.

Lingering Cold:

Temperatures and wind chills continue to plummet across north- central Montana as the Arctic airmass settles in. Given that temperatures and wind chills will remain relatively cold through the afternoon hours, the decision was made to extend the Cold Weather Advisory through Thursday morning to cover the bitter cold temperatures and wind chills expected. -thor

AVIATION

18/00Z TAF Period

Light snow continues to end from south to north. Overall the light snow should exit the northeast portions of the CWA by 03z. Breezy winds over North Central MT this evening will cause some blowing/drifting snow. Otherwise, the next concern will be the light snow developing on Wed morning over Southwest MT, which will steadily move northward during the day. The light snow will overspread much of the CWA by 00z Thur. IFR conditions or lower are expected in areas of snow on Wed. Mountains/passes will be obscured across much of the CWA through the period. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 32 -5 1 -8 / 100 40 50 40 CTB 21 -13 -4 -18 / 100 40 40 20 HLN 39 -3 8 -6 / 100 20 70 50 BZN 43 9 20 -2 / 70 20 60 70 WYS 32 7 28 -2 / 100 60 80 80 DLN 41 17 26 6 / 70 20 60 60 HVR 40 -8 6 -12 / 100 50 10 30 LWT 44 -5 6 -9 / 60 30 30 60

TFX WATCHES/WARNINGS/ADVISORIES

Extreme Cold Warning until noon MST Wednesday for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera- Eastern Toole and Liberty-Northern High Plains.

Cold Weather Advisory until noon MST Thursday for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft- Eastern Pondera and Eastern Teton-Gates of the Mountains-Hill County-Northern Blaine County-Southern High Plains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.

Winter Weather Advisory until noon MST Wednesday for Beaverhead and Western Madison below 6000ft-Big Belt, Bridger and Castle Mountains-Gallatin Valley-Madison River Valley-Missouri Headwaters.

Winter Weather Advisory until 11 PM MST Wednesday for Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains.

Cold Weather Advisory from noon Wednesday to noon MST Thursday for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty-Northern High Plains.