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FXUS65 KBYZ 100843 AFDBYZ

Area Forecast Discussion National Weather Service Billings MT 143 AM MST Sun Dec 10 2023

DISCUSSION

Today through Monday...

Pressure gradient from IDA-LWT was a healthy 18.6mb at 08z, with drops of about 1mb/hr over the past several hours, while mesoanalysis shows 50 knot westerly winds at 700mb. The setup for strong gap flow (including the stability) was very good and the Livingston airport reached a peak gust of 70 mph a little before midnight. Strongest pressure falls are beginning to shift east and the isallobaric component of wind has recently pushed gusts up to 60 mph at Big Timber and 50 mph at Harlowton. Even Fort Smith reported a 50 mph gust. As for timing, the gap areas will see peak gusts end by 12z, while northern Sweet Grass into Wheatland persist til 18z. Overall wind highlights for our western foothills look good and will make no changes at this time.

Satellite imagery shows a weak shortwave moving across southern AB and a Pacific moisture plume moving thru the PacNW and northern Rockies. We are starting to pick up some mountain snow in our west. West aspects should see 4-8" of snow over the next 24 hours.
Lower elevations will see low chances (10-20%) of light snow showers or flurries from now thru 15z, mainly east of the strongest downslope winds. Temps over the west half of our forecast area have warmed since the evening and are in the 30s to lower 40s...while our far east is in the teens. We will see highs in the 40s to near 50F today. Breezy west winds (20-35 mph gusts)
will push across the plains behind the shortwave passage.
Foothills winds will decrease thru the afternoon but will remain somewhat breezy tonight.

A shortwave currently over the Yukon will drop thru central Canada tonight, as weaker energy moves thru BC to the northern Rockies. The combination of these two features will (1) introduce a modest Canadian cold front into our area on Monday, and (2)
bring a brief chance of light/wet snow to lower elevations, especially close to the foothills. Forcing is quite weak but the shift to upslope winds at least gives us the opportunity for a little precip. GEFS and EC ensemble means are in agreement in showing 0.05-0.10" west and south of a Harlowton-Billings-Sheridan line. Surface temps will likely be in the 30s during times of precip so do not see much chance of any accumulation except perhaps along the foothills where 0.5-1.0" of wet snow is possible. As surface high builds in behind the precip and temps cool, this could result in some icy roads along the foothills by Monday evening. Something to think about for places like Livingston, Red Lodge and Sheridan. Otherwise, Monday's high temps (upper 30s to mid 40s) will be achieved in the morning as cold advection arrives between 15-18z.

Here are some notable probabilities over the next 36 hours: -50 mph gusts today: Livingston/Big Timber 100%, Harlowton 90% -60 mph gusts today: Livingston 100%, Big Timber 75%, Harlowton 65% -70 mph gusts today: Livingston 50%, Big Timber/Harlowton 5% -Beartooth/Absaroka snowfall: 4+ inches 70%, 6+ inches 25% -Measurable snow Monday: lower elevations 30%, foothills 70% -Snowfall of 1" Monday: lower elevations 0%, foothills 20%, mtns 80%

JKL

Monday Night through Saturday...

Upslope flow from Monday's cold front will linger into the evening and allow very light snow to persist, though additional accumulation's will remain low (under an inch). Downsloping winds will return on Tuesday alongside a very prominent upper ridge.
Monday's shortwave becomes a deep upper low over the southern CONUS, keeping Montana sandwiched between. Benign weather is expected for the rest of the week, with temperatures 5-10 degrees above normal almost each day. Next shot of moisture is Friday, but the shortwave that could bring is contains a lot of uncertainty, and so few ensembles show any precip potential, that most areas currently have less than a 20% chance for precip to occur. If any does occur, snow/rain amounts will be very light. Winds will be off and on breezy across the foothills west of Billings through this period, with at best a 30% chance for gusts to exceed 50 mph.
If there's any time that seems the windiest, it's Tuesday and Wednesday evenings and nights.

Vertz

AVIATION

VFR will prevail at the lower elevations over the next 24 hours, while western mountains (Beartooth/Absarokas and Crazies) will be frequently obscured in snow. Strong SW-W winds will impact the western foothills (KLVM-K6S0-KHWQ) today, with highest gusts (40-55 knots) during the morning. Gusts will decrease to 25-35 knots this afternoon and tonight. JKL

PRELIMINARY POINT TEMP/POPS

Tdy Mon Tue Wed Thu Fri Sat ------------------------------------------------------- BIL 047 033/041 024/042 027/048 030/047 027/043 029/048 1/N 14/O 20/U 00/U 00/U 11/B 00/B LVM 043 030/041 024/042 022/047 025/045 025/044 026/048 4/O 24/S 20/U 00/U 00/B 10/B 00/B HDN 049 028/043 021/042 021/049 021/048 023/044 022/049 1/E 14/O 00/U 00/U 00/U 11/B 00/B MLS 044 027/038 016/037 021/046 022/045 023/040 022/046 1/M 02/O 00/U 00/U 00/U 00/B 00/B 4BQ 046 028/042 021/042 025/048 027/047 024/041 024/048 1/M 02/S 00/B 00/U 00/U 00/B 00/U BHK 040 021/036 008/035 018/044 022/042 018/038 018/043 1/M 02/S 00/U 00/U 00/U 00/B 00/U SHR 047 026/042 021/040 019/049 023/050 022/044 022/052 1/E 13/O 20/B 00/U 00/U 11/B 00/U

BYZ WATCHES/WARNINGS/ADVISORIES
MT...Wind Advisory remains in effect until 11 AM MST this morning FOR ZONES 65-66.
High Wind Warning remains in effect until 5 PM MST this afternoon FOR ZONES 141-172-228.
WY...None.

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