textproduct: Great Falls

KEY MESSAGES

- Two major weather events will affect the CWA later this week, the first being strong winds Wed into Thu, with the second being heavy snow along the Rocky Mountain Front Wed night thru Sat.

- Mild temperatures early this week, turn a bit cooler by late in the week.

DISCUSSION

- Meteorological Overview: An upper level system continues to move from west to east across the CWA this afternoon. This is resulting in a few scattered rain/snow showers over the CWA. Expect the shower activity to decrease after Midnight.

An upper level trof will reside over the CWA for Tue into Wed, before the trof become more westerly by Wed evening. This will result in very strong winds developing over North Central MT Wed night into Thu. Overall, there is the potential for strong wind gusts over the entire CWA by Thu, thus the entire CWA is under a high wind watch by Thu. Additionally, this will be a very moist westerly flow. This will result in widespread heavy precipitation falling along the Rocky Mountain Front. The airmass will be cold enough, that most of the precipitation will fall as snow. Snowfall amounts will likely be measured in feet between Thu and Saturday. Additionally, the strong winds at the beginning of the event will likely result in near blizzard conditions.

For Fri into Saturday, an upper level trof redevelops in the wake of the strong winds from Thu. This will allow for a good chance for precipitation over much of the CWA. Again, with colder air moving south from Canada, much of the precipitation will fall as snow at all elevations. It is not until Saturday night that the upper level trof begins to exit the CWA, slowly ending the precipitation then.

Sun into Mon...warm air advection tries to move in from the Pacific Northwest Sun into Mon. This will result in another period of rain/snow to move across the CWA, but expect warmer temperatures to also move in as well by Monday.

- Forecast Confidence & Scenarios: There is over an 80 percent chance of much of the CWA seeing wind gusts over 60 mph on Thu, with mountain areas seeing over an 80 percent chance of wind gusts over 75 mph.

There is over an 80 percent that the Rocky Mountain Front sees over 2 feet of snowfall from Thu thru Sat. Brusda

AVIATION

09/18Z TAF Period

Westerly winds will once again become strong and gusty between 09/18z and 10/02z, with mountain wave turbulence and instances of low level wind shear remaining a concern through at least 03-06z Tuesday. Periods of low clouds will linger across central and southwest Montana through the TAF period with mountain obscuration remaining an on-and-off concern over the next 24 hours. -thor

PRELIMINARY POINT TEMPS/POPS

GTF 19 38 21 45 / 10 20 0 20 CTB 12 34 18 40 / 10 20 0 20 HLN 22 38 20 47 / 10 30 0 30 BZN 19 37 14 47 / 10 30 10 0 WYS 17 32 5 35 / 10 40 20 10 DLN 20 36 16 45 / 0 10 0 10 HVR 17 40 19 46 / 10 10 10 10 LWT 19 36 16 42 / 10 30 20 20

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Watch from Wednesday evening through Thursday afternoon for Beaverhead and Western Madison below 6000ft-Big Belt, Bridger and Castle Mountains-Canyon Ferry Area-Cascade County below 5000ft-East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Elkhorn and Boulder Mountains- Gallatin Valley-Gallatin and Madison County Mountains and Centennial Mountains-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-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Southern High Plains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.

Winter Storm Watch from Wednesday evening through Friday afternoon for East Glacier Park Region-Southern Rocky Mountain Front.

High Wind Watch from late Wednesday night through Thursday afternoon for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Hill County-Northern Blaine County-Snowy and Judith Mountains.