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FXUS65 KTFX 052343 AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT 444 PM MST Tue Dec 5 2023

UPDATED AVIATION SECTION

SYNOPSIS

A strong ridge over the Northern Rockies through Wednesday will continue to support mild and in some cases near record temperatures, in addition to strong and gusty southwest to west surface winds. By Wednesday night a cold front will begin to sweep southeast across the region, which will help to cool temperatures and bring a return in precipitation chances to most lower elevations.

DISCUSSION

Rest of today through Wednesday...primary forecast concerns throughout the period will be the continued threat for strong to high winds and unseasonably warm temperatures.

H500 ridge axis will shift east of the Northern Rockies through this evening; however, anomalously high heights of 1-2 standard deviations above normal will linger over the Northern Rockies through the day on Wednesday. Anomalously warm H700-H500 air of 1-2 standard deviations above normal will remain over the Northern Rockies through the day on Wednesday beneath this ridge, which combined with strong and gusty downsloping winds will help to support a very mild night tonight over the plains of Central and North Central Montana and near record high temperatures on Wednesday for most lower elevations north of the I-90 corridor. Some plains locations tonight may not even fall below 45 to 50 degrees, which is some 25 to 30 degrees above normal. High temperatures on Wednesday are expected to warm into the 50s across most lower elevations of Southwest Montana and the mid-50s to mid-60s in the valleys/plains of Central and North Central Montana, with numerous climate sites across these valley and plains locations being within 5 degrees of record high temperatures.

H700 cross barrier flow of 40-60kts will remain in place over the Northern Rockies through Wednesday, which will help to maintain strong and gusty southwest to west surface winds over much of the CWA through this timeframe; however, the threat for High Winds, specifically along the Rocky Mountain Front, is expected to decrease through the evening hours tonight as the surface pressure gradient relaxes slightly. While a few isolated wind gusts in excess of 58/75mph are possible beyond the current High Wind Warning endtime of 04z Wednesday beneath mountain wave activity (along the Rocky Mountain Front), I believe that the threat for widespread High Winds will decrease enough to allow for the cancellation of the High Wind Warnings. Never-the-less, strong and gusty southwest to west winds will continue to occur through Wednesday along the Rocky Mountain Front and across much of the CWA, with the latest NBM probabilistic data supporting between a 30-60% chance for wind gusts to exceed 41kts across most lower elevations. - Moldan

Wednesday night through Tuesday...The weather pattern will shift to a more brisk westerly flow later this week and into the weekend. Overall, the forecast models are in fairly good agreement for the overall weather pattern, but they do differ in the placement of the light precipitation. The first wave of precipitation should affect the CWA Wednesday night into Thursday.
There is about at 70 percent chance for 1 to 3 inches of snow in the Marias Pass and in the West Yellowstone areas during this time. Thus a winter weather advisory might be needed. Elsewhere, the chances for accumulating snow are very minimal for this event.
As we go into the weekend, colder air will be moving in, and the snow will become a bit more widespread. However, it looks to be quite light over the weekend. There is a 60 percent chance for another 1 to 3 inches of snow over the Rocky Mountain Front and in the West Yellowstone area this weekend, with less than a 10 percent chance elsewhere east of the divide. Seasonable temperatures are expected for early next week, as the chance for precipitation slowly decreases. Brusda



AVIATION
444 PM MST Tue Dec 5 2023 (06/00Z TAF Period)

VFR conditions will continue across North Central, Central, and Southwest Montana through at least 07/00Z with passing mid- and high-level cloudiness.

However, the main area of concern will be winds. A persistent moderate westerly flow aloft will continue mountain wave turbulence and low level wind shear across the area through at least 18Z. At the surface, south to southwest winds of 15 to 25 kt with gusts mostly to 35 kt will decrease through 06Z at the terminals as these winds start to decouple. However, winds over ridge tops and especially on the Rocky Mountain Front will continue gusts between 50 and 60 kt at times. -Coulston

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

PRELIMINARY POINT TEMPS/POPS
GTF 49 62 41 47 / 0 10 30 30 CTB 41 55 34 37 / 10 10 50 50 HLN 37 57 35 46 / 10 0 50 60 BZN 33 54 31 40 / 0 0 50 70 WYS 23 41 26 30 / 20 10 100 100 DLN 32 50 33 41 / 10 0 50 50 HVR 45 60 38 42 / 30 10 40 50 LWT 45 59 37 49 / 10 0 20 30

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 9 PM MST this evening for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera- Northern High Plains-Southern High Plains.

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