textproduct: Great Falls

KEY MESSAGES

- Snow will continue across the area through Monday morning.

- Well normal temperatures persist through Tuesday, with Monday night through Tuesday morning seeing low temperatures dipping into the teens.

- Moderating temperatures from Wednesday through Friday with mostly dry weather.

DISCUSSION

Additional Snowfall through Monday morning...

Snow will continue across much of Southwest through North Central Montana as moisture from the remnants of Rachel streams north and east from the Desert Southwest/Great Basin and over the Northern High Plains through Monday morning. Latest Hi-Res Ensemble Forecast (HREF) guidance suggests that snowfall rates of between 0.25-0.5" per hour will be common from the afternoon hours today through early morning hours on Monday across Southwest and portions of Central Montana as strong ascent associated with a shortwave embedded within the southwest flow aloft lifts north and over the Northern Rockies. There are even that northerly upslope areas could see rates approach 1" per hour, mainly between 6PM and midnight tonight. Most areas along and north of I-90 and south of the Montana Hwy 200 corridor can expect to see 4" to 8" of additional snowfall through Monday morning, with amounts near 12" in the northern slopes/foothills of the Rocky Mountain Front, Island Ranges of Central Montana, and Elkhorn and Boulder Mountains between 3500- 6500ft.

Given the additional heavy snow across these areas the Winter Weather Advisory for Fergus County below 4500ft, Helena Valley, Missouri Headwaters, and Madison River Valley was upgraded to a Winter Storm Warning. Additional tree damage and isolated power outages can be expected in areas covered by a Winter Storm Warning given the heavy, wet nature of the snow.

Cold Temperatures Monday night/Tuesday morning...

Clearing skies, light winds, and a relatively fresh snowpack will result in the coldest temperatures of the upcoming week, with the low end of guidance suggesting that lows could fall into the upper single digits above zero. - Moldan

AVIATION

11/18Z TAF Period

Widespread snowfall will continue across all terminals the exception of KWYS which will start initially as rainfall before switch to snow in the later half of the TAF period. Widespread low ceilings and visibilities will continue throughout much of the period with modest improvements towards the very end of the TAF period as our low pressure system continues to move east. Mountain obscuration will continue. -JR

PRELIMINARY POINT TEMPS/POPS

GTF 25 34 21 41 / 100 40 0 0 CTB 22 34 19 46 / 100 40 0 0 HLN 26 36 22 41 / 100 20 0 0 BZN 22 36 20 42 / 100 10 0 0 WYS 21 41 21 44 / 100 50 20 10 DLN 22 35 23 42 / 100 30 10 0 HVR 23 38 19 44 / 100 60 0 0 LWT 23 34 19 41 / 100 40 0 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-Fergus County below 4500ft-Gallatin Valley- Gates of the Mountains-Helena Valley-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Madison River Valley-Meagher County Valleys-Missouri Headwaters-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-Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Western and Central Chouteau County.