textproduct: Great Falls

KEY MESSAGES

- Rain and snow will overspread much of the CWA overnight.

- Potential for periods of snow Thu over Central and Southwest MT.

- Cooler temperatures Thu/Fri, before warmer and windy conditions return over the weekend.

DISCUSSION

- Meteorological Overview: A Pacific cold front is slowing move eastward across Montana overnight. Expect rain/snow to develop along the front, with the rain changing to snow for most areas by Thu morning. Periods of snow and colder temperatures are expected on Thursday, especially over Central and Southwest MT.

It will start to warm up a bit on Friday, but more noticeably over the weekend. Expect windy conditions to develop on Saturday, with periods of stronger wind then continuing into Monday.

For Monday through Wed of next week, an upper level trof is forecast to develop over the northern Rockies. This would allow for cooler temperatures and daily chances for rain or snow to develop over much of the CWA.

- Forecast Confidence & Scenarios: The main concern tonight/Thu is when does the rain change to snow. The current freezing height is just over 8000 feet, so it is going to take some time to cool the surface temperatures down to freezing along with air just above the surface. Overall, most places should change over to all snow by Thu morning. The winter weather advisory was expanded a bit to include more mountain passes along the divide and over Central MT. The advisory might need to be expanded later tonight or on Thu morning for some lower elevation locations should the snowfall rates be a bit heavier than currently thinking. Otherwise, expect a cooler day across the CWA.

There is near a 100 percent of warning criteria wind gusts on Saturday along the Rocky Mountain Front and adjacent Plains. High wind statements will likely be issued later tonight or on Thu for this weekend.

For early next week, the GFS/EC both want to bring down another wave of colder temperatures and precipitation. However, they continue to differ on how cold/how much precipitation. Right now, it is looking rather unsettled with below normal temperatures a possibility for a portion of next week. Brusda

AVIATION

04/18Z TAF Period

An approaching Pacific weather system will begin to bring rain to lower elevations this afternoon and evening, tracking east to west through Thursday morning. Warm temperatures will have the precipitation type start with all rain, until a cold front switches to a snow/rain and snow mix. Warmer temperatures will keep snow accumulations light, but the front may bring brief IFR visibilities, particularly in the Southwest MT valleys. There's a 20% chance for visibility to drop below a mile briefly in Southwest MT Thursday morning. With this system, clouds will lower to MVFR to IFR at times through Thursday morning. -Wilson

FIRE WEATHER

There is still the potential of fire weather concerns this weekend for the grassland areas that don't receive much precipitation Thu/Fri. The gusty winds could create difficult conditions to contain any new fire starts over the weekend. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 33 46 28 47 / 70 70 60 20 CTB 29 46 24 46 / 40 50 40 0 HLN 33 46 27 45 / 90 80 50 30 BZN 30 43 24 44 / 80 90 60 30 WYS 24 35 15 36 / 80 90 60 30 DLN 32 42 21 42 / 90 70 20 10 HVR 27 44 22 49 / 60 50 20 10 LWT 32 41 23 42 / 20 80 60 30

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 11 PM this evening to 3 PM MST Thursday for Little Belt and Highwood Mountains.

Winter Weather Advisory from 8 PM this evening to 9 AM MST Thursday for Elkhorn and Boulder Mountains-Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory from 8 PM this evening to 3 PM MST Thursday for Big Belt, Bridger and Castle Mountains-Gallatin and Madison County Mountains and Centennial Mountains.

Winter Weather Advisory until 9 AM MST Thursday for Northwest Beaverhead County.