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FXUS65 KTFX 081726 AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT 1026 AM MST Fri Dec 8 2023

UPDATE



SYNOPSIS

Areas of primarily mountain snow will generally subside through the day. A dry and seasonable day is expected Saturday before gusty west winds develop across much of the plains Saturday night into Sunday.
Precipitation this Sunday into Monday will largely reside along the

UPDATE

Allowed the Winter Weather Advisory in effect for East Glacier Park area to expire. Additionally, opted to cancel the Winter Weather Advisory for the Little Belts that was originally scheduled to be out til 11 AM this morning. Any additional snow looks to be less than a half an inch in this area through 11 AM.
Satellite imagery is showing plenty of low clouds/fog in wake of clearing skies across western portions of the North-central Montana plains this morning. Webcam images and surface observations along I-15 near and north of Shelby suggest this is mostly low clouds. At this point, the only sensor showing significantly reduced visibility due to fog is the Cut Bank Airport. Given fog appears to remain patchy, will opt to continue to handle it with a Special Weather Statement. -AM

Second Update...

Main change to the forecast this morning was to adjust hourly temperatures back towards what has been occurring this morning.
Otherwise, the POPs are on track this morning and more or less aligned to where snow is falling, so no other changes were made to the forecast this morning. Ludwig

AVIATION
1006 AM MST Fri Dec 8 2023 (08/18Z TAF Period)

Unsettled northwest flow over the Northern Rockies will help to maintain MVFR/low-VFR conditions across most terminals throughout the 0818/0918 TAF period; however, periods of snow and/or low CIGS in northerly upslope areas may periodically reduce conditions to LIFR/IFR. Mountains will be obscured for much of the 24 hours. - Moldan

Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information.

PREV DISCUSSION
The rest of today and Saturday... To start the period, a broad, somewhat disorganized upper level trough is overhead and slowly shifting eastward across the Northern Rockies and Northern Great Plains. Weak embedded features in this broader trough are continuing to ripple through the flow aloft, helping support generally light snowfall across portions of the region this morning. The going Winter Weather Advisories are largely in good shape. Consideration was given to trimming back the end time a bit for some advisories, but will allow for subsequent shifts to monitor trends this morning before canceling any advisories early. Worth mentioning is that forecast soundings dry out from the top down this morning across the eastern plains of North-central Montana, giving a small window for some light freezing drizzle. Confidence in widespread freezing drizzle is relatively low at this point. Otherwise, added mention of patchy fog across most of North-central Montana this morning, but primarily for western portions of the plains, as clearing skies and light winds will promote strong radiational cooling.

The back end of the aforementioned upper level trough will swing across and east of the area tonight. Any snow that lingers into this afternoon and evening looks to be minor. Dry conditions then move in briefly for tonight into Saturday as shortwave ridging aloft moves overhead.

Saturday night through much of next week... As quick as the upper level shortwave ridging moves in, it will move out equally as fast Saturday evening as a series of upper level disturbances move across the region. Northwesterly flow in the mid levels and aloft turns more westerly Saturday night, resulting in strengthening winds across North-central Montana into Sunday. The strongest winds look to remain along the Rocky Mountain Front out to the Cut Bank area, where a High Wind Watch remains in effect. The atmospheric profile (Ridgetop stability, strong winds in the stable layer) looks favorable for stronger winds Saturday evening into Sunday, but recent probabilistic guidance has trended a bit down, giving a 50/50 chance for a peak gust in Cut Bank of 55 mph over this period. This lack of increased confidence is what led me to continue the High Wind Watch at this time. Trends will continue to be monitored for this period.

The aforementioned upper level disturbances will allow for periods of mainly mountain snow Sunday into early next week. At this point, most snow looks to fall along the Continental Divide and across the mountains of Southwest and Central Montana. The probability for 4 inches of snow over Marias Pass between Sunday morning and Tuesday morning is around 40%.

Ensembles are in relatively good agreement for a cutoff low to develop well off to the south Tuesday and Wednesday, with a broad ridge of high pressure building in overhead. This lends to temperatures trending warmer than average, with relatively low chances for precipitation. A subset of ensemble members bring unsettled conditions back into the picture for late next week, decreasing confidence that the upper ridge will persist into next weekend. -AM



PRELIMINARY POINT TEMPS/POPS
GTF 39 24 38 31 / 20 40 0 10 CTB 34 19 33 25 / 30 30 0 0 HLN 36 21 37 26 / 20 10 0 10 BZN 33 14 33 19 / 40 20 0 10 WYS 25 -2 20 10 / 70 20 0 40 DLN 30 9 29 18 / 50 0 0 10 HVR 36 21 37 24 / 50 10 0 10 LWT 35 21 36 22 / 40 30 0 10

TFX WATCHES/WARNINGS/ADVISORIES
High Wind Watch from Saturday evening through Sunday afternoon for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains-Southern High Plains- Southern Rocky Mountain Front.

Winter Weather Advisory until 11 AM MST this morning for Bears Paw Mountains and Southern Blaine-Northwest Beaverhead County.

Winter Weather Advisory until noon MST today for Snowy and Judith Mountains.

Winter Weather Advisory until 3 PM MST this afternoon for Gallatin and Madison County Mountains and Centennial Mountains.

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