textproduct: Great Falls

KEY MESSAGES

- Periods of moderate to heavy mountain and lower elevation snow continues on and off through Saturday.

- Gusty winds expected in Southwest Montana Friday and Saturday.

- Warmer temperatures move in next week, with light precipitation in mainly the mountains.

DISCUSSION

- Meteorological Overview:

Pacific moisture continues to stream into the region. This moisture overriding the colder airmass will continue to fill in snow across North-Central MT tonight. Widespread snow is expected through Friday morning. A mid-level convergence zone across the MT Highway 200 corridor, will bring periods of moderate to heavy snow along that strip through the night and into Friday morning. The surface front will continue to stall out along the Missouri Headwaters region, with the mid-level front wavering a bit north- south of the MT highway 200 corridor through Saturday. This will bring periods of widespread snow for places mostly north of I-90/Missouri Headwaters through Saturday, with moderate and heavy snow more concentrated across Central/North Central MT. Orographically enhanced snow continues along the Continental Divide and mountains through Saturday. The higher moisture content will help aid in continuing moderate to heavy snow at mountain passes.

Most of the mountain snow in Southwest MT will be above pass level due to the warmer conditions south of the front. Though overnight temperatures dropping close or below freezing will allow for some light snow to develop. The main concern in Southwest MT will be gusty winds Friday and Saturday. Friday, decent mid-level winds will try to mix down to the surface in the afternoon. Saturday looks to be mostly pressure gradient driven as that low finally pushes southeast out of the region. Convective showers look to develop as this system tries to push in colder air Saturday afternoon and evening into Southwest MT, with a slight chance for a few locally heavy snow showers/snow squalls.

Heading into next week, we transition to a northwest flow aloft pattern with the ridge building in the Western U.S. A few disturbances will moves through the area throughout the week, bringing light precipitation and windy conditions. Another strong mid level jet moves into the Rocky Mountain Front and Central MT late Monday and Tuesday, which could potentially bring another round of strong winds. Warm temperatures move in by mid-week. Overnight cold temperatures in the low to mid 30s should limit any flooding concerns due to snow melt.

- Forecast Confidence & Scenarios:

Snow Through Saturday:

High confidence remains in heavy snowfall developing along the Continental Divide and Central MT mountains overnight tonight, continuing on and off through Saturday afternoon. Current mid level frontogenesis will continue moderate to heavy snow bands in Fergus and Judith Basin Counties at times. Snow filling in across North-Central MT tonight will bring some moderate to heavy snow banding, but it will be more localized tonight. Better chances for moderate to heavy snowfall at lower elevations across North- Central MT will be Friday night to Saturday. Any wet pavements from this evening will freeze and become slick overnight, which will affect the Friday morning and evening commutes regardless in how much snow falls overnight.

One area of uncertainty in snowfall amounts is the Hi-line/Chouteau County. So far they are on the cutoff line where better snow banding develops Friday night into Saturday. Depending on where the convergence zone sets up, they could get more or less than forecasted. We will have to watch for any upgrades to the Winter Weather Advisory, especially Chouteau County. Saturday, we will have to watch for the slight potential in the development of snow squalls, especially in Southwest MT. A front bringing in colder air aloft looks to drop surface wet bulb temperatures below freezing, so dynamic cooling could help push temperatures to freezing and develop moderate to heavy snow showers. -Wilson

AVIATION

13/06z TAF Period

Light snow will affect much of North Central MT through the period. Some short breaks are possible, but overall expect near IFR conditions or lower through the period. For Southwest MT, it will not be as bad. Some rain/snow showers will pass through the terminals, but a long lasting precipitation is not expected at this time during this period over SW MT. Mountains/passes will be obscured across the CWA through the period. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 45 27 34 25 / 40 70 100 90 CTB 36 20 29 18 / 60 70 80 70 HLN 48 33 44 31 / 70 80 100 100 BZN 57 34 55 36 / 20 50 70 60 WYS 49 31 45 30 / 40 40 60 60 DLN 53 37 56 38 / 50 20 30 40 HVR 47 22 35 20 / 70 40 50 60 LWT 48 23 32 21 / 60 100 100 100

TFX WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 6 PM MDT Saturday for Big Belt, Bridger and Castle Mountains-Cascade County below 5000ft-East Glacier Park Region-Eastern Pondera and Eastern Teton-Elkhorn and Boulder Mountains-Fergus County below 4500ft-Gates of the Mountains-Helena Valley-Judith Basin County and Judith Gap- Little Belt and Highwood Mountains-Meagher County Valleys- Northern High Plains-Northwest Beaverhead County-Snowy and Judith Mountains-Southern High Plains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass.

Winter Weather Advisory until 6 PM MDT Saturday for Bears Paw Mountains and Southern Blaine-Eastern Glacier, Western Toole, and Central Pondera-Eastern Toole and Liberty-Western and Central Chouteau County.