textproduct: Great Falls

KEY MESSAGES

- Snow & rain showers continue along the Rocky Mountain Front this afternoon and into Thursday.

- A cold front brings cooler temperatures Thursday and Friday.

- Increasing chances for widespread precipitation this weekend.

DISCUSSION

- Meteorological Overview:

Zonal to southwest flow aloft this afternoon into Thursday will continue to stream moisture over the Continental Divide. As a result, isolated to scattered rain/snow showers will be persistent primarily along the Northern Continental Divide and Rocky Mountain Front this afternoon into Thursday morning. A cold front currently along the Hi-Line pushes south across the state today into Thursday, bringing cooler temperatures to the region for Thursday and Friday. The front also brings another slight chance for patchy fog to develop across North-Central MT tonight into Thursday and Friday morning.

A digging trough from British Columbia/Pacific Northwest Coast increases southwest flow aloft, bringing warm air advection and moisture Friday. Precipitation chances increases throughout Friday across Southwest MT. However, better chances for widespread precipitation across the state arrives Saturday into Sunday with a low pressure system, with precipitation lingering into Monday. So far, the main message with this system is minor snow at pass level with more moderate accumulations at the higher mountain peaks, and rain/snow at lower elevations (light snow trending more late Sunday into Monday).

Behind that system, ensembles are hinting at a ridge building in for the middle of next week. This trends drier conditions with temperatures building back to near or above normals, with some uncertainty in how much of a warm up there is.

- Forecast Confidence & Scenarios:

Fog Tonight:

Low-level subsidence behind this cold front passage can allow for patchy fog development across North-Central MT later tonight into Thursday morning. There's a 30-60% chance for fog to develop across North-Central MT, isolated 10-30% chances for visibility to drop to a half mile or lower with fog. One limiting factor is a low stratus deck prohibiting fog development. The potential for fog development extends into Friday morning as well with higher- res and medium-res models showing low level moisture lingering. Depending on how deep that low level moisture is, there is a very low chance for light freezing drizzle to develop along the Rocky Mountain Front (10% chance).

Snow Along Northern Rocky's Through Thursday:

Not much has changed in terms of the forecast and impacts of the snow along Marias Pass and the Rocky Mountain Front foothills. Minor snow accumulations of 2-4" is expected along Marias Pass, with little accumulations towards the Rocky Mountain Front. Weak low level frontogenesis along the cold front can bring moderate snow rates along the mountains this evening.

Weekend Storm System:

There remains some uncertainty with the weekend storm system as the low track will play into snow accumulations. Warm air advection Friday into Saturday may make snow accumulations struggle along mountain passes/higher Southwest MT valleys, keeping the bulk of the snow at the higher peaks. Models have been trending colder air moving in Sunday on the back edge of the low pressure system, where there will be better chances for minor snow accumulations at mountain passes. There's a 20-60% chance for 3" of snow at pass level in Southwest MT. Light snow looks to mix down to lower elevations Sunday/Monday morning at times but accumulations look to be light to minimal at this time. -Wilson

AVIATION

28/18Z TAF Period

Areas of low clouds and some patchy fog near the International border, including KCTB and KHVR, will improve some this afternooon but MVFR Cigs remain possible. Snow showers are primarily limited to areas near the continental divide with a few light showers and periods of mountain obscuration extended further east at times over the central MT mountains and vicinity through this evening. Breezy west to northwest winds across central and southwest MT will diminish tonight with winds becoming light or shifting to the northeast across the north- central MT plains. With the wind shift, areas of low clouds and patchy fog may expand as far south as KGTF by Thursday morning. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 28 40 30 40 / 0 0 0 0 CTB 25 35 26 36 / 50 0 0 10 HLN 26 48 28 46 / 0 0 0 0 BZN 24 47 26 45 / 0 0 0 10 WYS 14 45 22 48 / 0 0 0 10 DLN 23 43 30 46 / 0 0 0 10 HVR 24 41 24 44 / 10 0 0 0 LWT 28 45 27 45 / 0 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 6 AM MDT Thursday for East Glacier Park Region.