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FXUS65 KBYZ 070907 AFDBYZ

Area Forecast Discussion National Weather Service Billings MT 207 AM MST Thu Dec 7 2023

DISCUSSION

Today through Friday night...

The warm upper ridge that has given the mild temperatures the last few days was in the process of sliding east. This will bring changes on the colder and more unsettled end of things, as a cold front moves through the area.

Winds along the western foothills have been strong overnight at Livingston but have underachieved, for the most part. Wind gusts have been in the low 50s at Livingston. Surface pressure gradient from Idaho Falls to Lewistown was sitting at only 10mb. Gradient progged to tighten up a bit through early morning, with some pressure falls occuring ahead of a cold front. These are broad pressure falls however, so this may not tighten the gradient much and may serve to keep the winds below Advisory criteria into early morning. NBM probabilities for 60mph at Livingston were still 60% through 5am. Will hold on to the Advisory a little longer and watch trends, but may be able to cancel early.

Winds will kick up over the central and eastern plains today as a cold front moves through. The timing of the front has been delayed some, so this will lead to highs in the lower 50s most places, and bring the strongest winds through this afternoon and tonight. 850mb winds of 30-35kts will produce wind gusts of 25-40mph this afternoon and this evening. NBM probabilities have a 40-50% chance of winds hitting 40mph across the area. The surface pressure gradient actually tightens up quite a bit over the eastern eastern zones tonight and Friday and this will crank the winds there. Wind gusts of 35-50mph can be expected over Custer, Power River, Carter and Fallon counties tonight through Friday, with the strongest winds over Fallon and Carter counties. NBM probabilities were showing a 70% of 45mph gusts at Baker and Ekalaka.

Scattered showers (40-60% chance) will develop today as the cold front races through the area. Chances go up east of Billings this afternoon and tonight with the chances being 60-80%. Probabilities for a tenth of an inch of QPF over the southeast was at 40%. The precipitation will be rain, with some snow mixing in with the rain late tonight. Snow will develop over northeast Montana tonight and swing southeast into Fallon and Carter counties Friday. This snow will be accompanied by the strong wind gusts mentioned in the paragraph above, to make for a nasty day. Probabilities were showing a 50% chance of 2 inches of snow for Baker and a 40% chance at Ekalaka. May need a Winter Weather Advisory for this event, considering that the wind will be strong too. Will give things another run or two to nail down timing and amounts further.
The mountains will get a shot of accumulating snow today and tonight, with lingering light snow Friday. Accumulations of 6-10 inches are expected along the west and northwest facing slopes of Beartooth/Absarokas with 3-6 inches over the west and northwest facing slopes of the Bighorns tonight and Friday. The chance of 6 inches of snow over west and northwest facing slopes around Cooke City was 60%. Amounts were below highlight criteria, but those with outdoor interests in the mountains through Friday should plan for winter weather.

Temperatures will be cooler today, but with the later frontal timing, highs will be allowed to reach the lower 50s most locations. Thoughts yesterday were for falling temperatures during the day today but believe temperatures will steady out instead, with a quick fall late afternoon and this evening. The strongest surge of cold air will be over the southeast will highs limited to the mid 39s of Friday (with snowfall). Central zones will have highs around 40 degrees on Friday. Lows will fall into the 20s and teens Friday night. TWH

Saturday through Thursday...

Saturday begins with a mild shortwave passing over southern and eastern MT, but it's a very dry shortwave that is expected to not produce any precipitation. It's followed up by broad ridging that contains a couple embedded shortwaves in it as well. The first items to note is that a strong pressure gradient sets up across south-central MT, increasing the likelihood of a gap flow to occur for the Livingston area overnight. This area currently contains a 85% chance of seeing winds exceed 50 mph, and a 64% chance of winds exceeding 60 mph. As pressures continue to fall lee-side of the Northern Rockies, the gradient becomes more west to east, and alongside 700 mb winds Saturday morning and afternoon being 40-50 kts, this sets up strong wind potential for ares along Highway 191 from Big Timber and north through Harlowton, with a 60-75% chance of winds exceeding 50 mph during this period. While all of this is going on, light snow is expected to occur over the mountains Saturday night into Monday morning, with 2-6" of snow possible over these 36 hours, with higher amounts focused at the highest elevations and the Cooke City area.

One last, weak trough will pass through late monday and bring a round of light rain/snow showers to the area, and slightly cooler temperatures (back down to near normal values from the weekend).
After that there is high confidence for a prominent upper ridge to set up over the northern part of the country and bring back above normal temperatures once again, and likely off and on periods of gap winds as well. Vertz

AVIATION

There is still a 70% chance for gusts to reach and exceed 45 kts at KLVM through the early morning, then winds should taper off through the day. Expect a rain/snow mix to occur at KLVM as well through this morning, but should be light, and only a 10% chance for surface visibility to drop below 1SM. All other terminals will be predominantly light rain through the early afternoon. Vertz

PRELIMINARY POINT TEMP/POPS

Tdy Fri Sat Sun Mon Tue Wed ------------------------------------------------------- BIL 052 031/041 026/040 026/048 030/040 024/041 026/048 5/R 13/S 20/U 00/N 22/O 11/B 00/U LVM 047 027/037 019/036 025/043 029/041 023/042 023/047 8/O 24/S 10/U 12/S 32/S 11/B 00/U HDN 054 029/043 022/042 021/049 028/043 021/042 021/049 7/R 14/S 20/U 01/B 22/O 11/B 00/U MLS 052 030/037 021/037 022/045 026/038 019/039 022/045 7/R 25/S 10/U 01/B 10/B 00/B 00/U 4BQ 053 031/038 023/037 023/046 028/040 021/041 023/048 6/R 24/S 10/U 00/B 01/B 00/B 00/U BHK 051 026/034 016/033 016/040 020/035 014/036 018/044 6/R 36/S 20/U 01/B 00/B 00/U 00/U SHR 052 025/039 021/038 018/047 025/040 018/041 020/051 4/R 44/S 30/U 01/E 12/O 11/B 00/U

BYZ WATCHES/WARNINGS/ADVISORIES
MT...Wind Advisory remains in effect until 9 AM MST this morning FOR ZONES 65-66.
WY...None.

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