textproduct: Great Falls

KEY MESSAGES

- Breezy through the remainder of the day in most areas.

- Locally breezy conditions develop Saturday ahead of a colder Spring system moving in late Saturday into Sunday.

- Mountain snow, with a mix of lower elevation rain and snow Saturday night into Sunday.

DISCUSSION

- Meteorological Overview:

Zonal flow aloft continues across the region this afternoon into tonight, with a small shortwave ridge moving through tonight ahead of a robust Pacific trough near the pacific NW coast arriving this weekend with active weather. Sufficient instability has developed to result in some showers near the Canadian border east of I-15/. THis activity, along with breezy winds, continues through the early evening before subsiding.

Aforementioned troughing begins to move in tomorrow, which will combine with sufficient daytime heating and cool air aloft to result in lower elevation showers and mountain snow showers, primarily from late morning through early evening. As orographic forcing takes over and snow levels fall tomorrow afternoon and evening as the core of the upper trough arrives, a stretch of more impactful snow develops south of I-90 and east of I-15, primarily in the terrain through Sunday morning.

Meanwhile, surface low pressure being carved out in Wyoming and southeast Montana through the day Saturday will result in a northerly winds developing, initially over the plains late afternoon into the evening hours Saturday. These northerly winds, which will be gusty at times, usher in cooler air from north to south across the region Saturday night into Sunday. The cooler air moving in will coincide with the best orographic and dynamical forcing, which will yield at least a brief opportunity for some lower elevation snow Sunday. The coldest night looks to be Sunday night, which will feature lows into the 20s for many areas.

Attempts are made at a ridge building in early next week, though embedded waves in the building northwest flow aloft will keep conditions unsettled and on the cooler side to open the week. This theme more or less persists through the remainder of the week, which will keep daily opportunities for showers around. -AM

- Forecast Confidence & Scenarios:

Snow levels Saturday afternoon and evening in SW MT:

Present timing of falling snow levels Saturday afternoon and evening results in snow beginning to mix in just after sunset at Bozeman and Ennis and adjacent areas. Should this transition be quicker with an overall cooler solution, some minor impacts from snow would develop in the Gallatin Valley and Madison River Valley.

At this time the timing of snow levels keeps impacts from the snow confined to higher elevation areas across SW MT, particularly the northern end of the Madison and Gallatin Ranges, where upslope enhancement will occur. Overall snowfall amount and duration appears to be lighter/more brief in nature for the Big Belts and Bridgers through the night Saturday, but trends will be monitored for changes in thinking.

Snow Sunday:

As better orographic left and synoptic forcing arrives late Saturday night into Sunday, additional periods of snow develop (Some rain does look to mix in at times at lower elevations). Areas where confidence is greatest in impactful snow is in the Little Belts and near Glacier NP, though there still remains uncertainty in overall amounts and timing. Should snow fall at night, there would be greater confidence in impacts, and vice versa. -AM

AVIATION

15/18Z TAF Period

VFR conditions will prevail at all terminals during this TAF Period. At the KHVR terminal there is a 15 - 20% chance for rain showers between 15/21Z and 15/24Z. At the KGTF and KHLN terminals there is a 15 - 40% chance for rain showers between 16/12Z and 16/18Z. At the KBZN terminal there is a 20 - 50% chance for rain showers and a 20% chance for thunder between 15/19Z and 15/24Z. At the end of this TAF Period there will be periods of mountain obscuration. -IG

PRELIMINARY POINT TEMPS/POPS

GTF 41 57 34 44 / 10 20 40 80 CTB 34 55 29 43 / 10 10 70 70 HLN 39 54 34 46 / 10 50 30 80 BZN 36 58 29 45 / 0 70 90 70 WYS 30 55 25 42 / 10 30 70 60 DLN 37 58 27 46 / 0 30 60 60 HVR 38 62 33 47 / 10 20 40 80 LWT 38 56 30 41 / 10 80 90 90

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 5 PM Saturday to 6 AM MDT Sunday for Gallatin and Madison County Mountains and Centennial Mountains.