Marine Weather and Tide Forecast for South Hills, MT

DISCUSSION

- Meteorological Overview:

A vertically stacked low in Idaho will continue to move to the east throughout the afternoon. The associated surface/700mb front has produced light to moderate snow across Southwest MT throughout the day. Marginal temperatures with the increased sun angle this afternoon has lead to most snow accumulations to remain on non pavement surfaces despite moderate snow rates. This system has been progressing slower than models throughout the day, which had lead to lower impacts of this system overall since the higher sun angle has warmed up the ground for less snow accumulations.
Southwest MT can expect to see additional widespread light to moderate snow through the afternoon/early evening, but additional accumulations will be mainly on non pavement surfaces. By the evening, the main low and mid level forcing will pull away.
However, northwest flow aloft will allow for additional scattered rain/snow showers through Friday morning across the region.
Colder air aloft combined with low instability in North-Central MT will also bring the low end chance for some graupel to mix in with a heaver rain/snow shower this evening.

This northwest flow aloft pattern through the weekend will allow for additional light snow to develop in the mountains, but lower elevations will generally remain dry through the day Sunday.
Starting on Saturday, high pressure builds in the Great Basin region, while a low deepens farther north into Canada. This will strengthen the surface pressure gradient along the Rocky Mountain Front and North-Central MT plains. This will begin a windy period for the plains through Monday. Better 700mb winds arrive Sunday, which will bring the period of strongest winds and become more widespread across the region. The strong chinook winds will bring back mild temperatures for the weekend. The warm, windy, and drier conditions at lower elevations brings a concern for elevated grassland fire risk. Later in the day Sunday through Monday, a Canadian front will push south through Montana. The front will help cut the strong winds, as well as bring cooler temperatures and light snow to the lower elevations.

The pattern next week will be more zonal, with a few waves of Pacific weather systems moving through. This will keep the week somewhat active with temperatures oscillating through the week.

- Forecast Confidence & Scenarios:

Snow Through Friday Morning:

The upper level front is currently passing through Gallatin and Fergus Counties at the moment. They can continue to see this widespread wet snow over the next few hours. Warm surface temperatures had made snow struggle to accumulate throughout the day. Southwest MT can still see a couple more inches of snow, with locally higher amounts at the peaks through the evening. Since impacts to roads will be minimal through the rest of the day, I've decided to let the Winter Weather Advisories expire at 3pm MST.
There will be additional rain/snow showers. Temperatures dropping into the 20s/teens overnight will allow for any wet pavements to freeze and become slick.

Winds Saturday Through Monday:

The strong winds Saturday will be mainly driven by the strengthening pressure gradient. The stronger winds look to be concentrated mainly along the Rocky Mountain Front, extending out to the Highway 200 corridor/US 87. There's a greater than 60% chance for 75 mph wind gusts along the Rocky Mountain Front foothills. Probabilities did decrease slightly across the plains since yesterday.There is up to a 40-70% chance for 58 mph wind gusts. The current High Wind Watches remain on track.

The strongest winds will happen Sunday, as stronger 700mb winds move into the region. This combined with the pressure gradient front and daytime mixing will bring in the strongest period of winds during the day Sunday. The gusty winds will spread much farther across the region. Along the Rocky Mountain Front foothills, there is a good chance for gusts to exceed 80mph. The probability for 90mph wind gusts have increased as well over the past day. Across the rest of the region, there's a 40-80% chance for 58mph wind gusts north of I-90. -Wilson



AVIATION
05/18Z TAF Period

Main concern will be light rain/snow that will affect Central/Southwest MT through the afternoon and into the evening.
Short periods of moderate snowfall are possible, but that will become less likely after 22z. Precipitation will be slow to diminish overnight. There is some potential for fog if we get any clearing, but overall cloudy skies are expected to prevail, preventing too much fog. More widespread VFR conditions are expected by late morning Friday. Mountains/passes will be obscured across much of the CWA through 12z Fri. Brusda

FIRE WEATHER

There will be elevated fire weather concerns for grassland areas this weekend. Particularly for areas that receive little to no precipitation today and Friday. Strong winds, gusting over 50 mph at times, combined with high temperatures in the 50s and 60s and minimum relative humidity values in the 20s and 30s may create difficulties to contain any existing or new fire starts. The worst conditions look to occur on Sunday when the winds will be strongest and most widespread. - RCG

PRELIMINARY POINT TEMPS/POPS
GTF 28 47 32 57 / 70 10 0 0 CTB 23 46 31 52 / 60 0 0 10 HLN 28 45 29 53 / 70 20 10 20 BZN 24 44 22 51 / 80 20 10 10 WYS 16 37 13 36 / 80 20 10 30 DLN 21 41 23 48 / 30 0 0 0 HVR 23 50 28 61 / 10 0 0 0 LWT 23 43 26 54 / 40 10 10 0

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

High Wind Watch from Saturday morning through Saturday evening for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft-Fergus County below 4500ft-Judith Basin County and Judith Gap-Western and Central Chouteau County.

Winter Weather Advisory until 3 PM MST this afternoon for Beaverhead and Western Madison below 6000ft-Big Belt, Bridger and Castle Mountains-Elkhorn and Boulder Mountains-Gallatin Valley-Little Belt and Highwood Mountains-Madison River Valley- Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Upper Blackfoot and MacDonald Pass.

Winter Storm Warning until 3 PM MST this afternoon for Gallatin and Madison County Mountains and Centennial Mountains.