626 FXUS65 KTFX 061156 CCA AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 450 AM MST Sun Nov 6 2022 Aviation Section Updated. .SYNOPSIS... Temperatures remain well below average through mid-week as a colder airmass settles in from Canada. Widespread snow develops late tonight and continues through Monday and Tuesday, as Pacific moisture lifts over the low level cold air. Snow gradually ends on Wednesday. Although not as cold, temperatures remain well below normal through the end of the week. && .DISCUSSION... Areas of light snow persist early this morning, but overall continue to gradually dissipate as the atmosphere stabilizes under shortwave ridging aloft. Surface winds have turned northerly across North-central Montana as colder air settles in from Canada. Temperatures will remain below average today with continued cold advection producing a few light snow showers. Widespread snow returns to the forecast late tonight through Monday. A mid-level warm front will lift Pacific moisture from the southwest late tonight, spreading light snow across much of North-central Montana through Monday. 25th-75th percentile snowfall amounts from the NBM range from around 1 to 3" for much of North-central Montana, trending upward a bit toward 2 to 5" north and west of Great Falls where the low level easterly flow will enhance the upslope flow into the Northern Rocky Mountain Front. This is only part of a complicated forecast. After the initial warm frontal passage aloft, an upper level jet streak arrives and begins to produce a band of heavier snow from northern Nevada, across southern Idaho, and into Southwest Montana. The combination of surface convergence, upper level divergence, and orographic lift will combine to produce deep dendritic growth layer within this snowband. While confidence is high enough to issue a winter storm watch for the Southwest Montana mountains, there remains considerable uncertainty in the position, and northward extent of the snow band further north into central Montana later Monday night. It is anticipated that winter weather advisories will be posted on a later forecast, but are withheld for now due to lack of confidence in the position and extent of the secondary snowband for areas north of I-90 later Monday night. The Arctic airmass deepens over the region on Tuesday, with an elongated cutoff trough over the western CONUS. Wind chill advisories may be needed as wind-chill temperatures dip toward -20F early Tuesday for portions of North-central MT. In the Southwest, snow is likely to continue as the upper level low slowly rotates through the interior west. Areas around West Yellowstone could be looking at a 4-day continuous snowfall from Monday through Thursday. Even further north, periods of light snow may occur on Wednesday as embedded shortwave energy moves through the southwest flow aloft. Snowfall comes to an end on Thursday, but cold air remains in place through late week and on into the weekend ahead. && .AVIATION... 450 AM MDT Sun Nov 6 2022 (06/12Z TAF period) A mix of VFR and MVFR conditions prevail this morning under areas of low cloud associated with a cold airmass moving into the area from Canada. Light snow showers linger across portions of North-central Montana, with an overall dissipating trend. Mostly cloudy skies become partly cloudy by afternoon. Moisture begins to increase again overnight, with chances for snow returning early Monday morning. Areas of snow are likely to become more widespread through the day on Monday. KWYS TAF will not be issued again until airport operations resume next spring. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 27 12 22 0 / 10 40 80 60 CTB 19 4 12 -6 / 20 80 100 40 HLN 37 16 25 7 / 0 40 80 70 BZN 40 19 36 13 / 0 60 80 90 WYS 31 17 38 19 / 0 90 100 100 DLN 36 20 35 15 / 0 60 90 80 HVR 25 10 25 5 / 0 20 80 70 LWT 30 12 30 5 / 10 20 70 80 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER STORM WATCH IN EFFECT FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR Ruby Mountains and Southern Beaverhead Mountains...Gallatin and Madison County Mountains and Centennial Mountains && $$ http://www.weather.gov/greatfalls