Three Forks, MT 59752 Weather

Key messages

- Areas of fog will redevelop across north-central MT tonight and may be locally dense with low visibility and some patchy icing of elevated surfaces.

- A Pacific weather system brings more widespread precipitation by Sunday with initially high snow levels eventually lowering to mountain passes late Sunday and Sunday night.

- Temperatures trend closer to average early next week.

Discussion

- Meteorological Overview:

Low clouds/stratus have spread into some SW MT valleys including areas as far south as the Gallatin Valley and Norris Hill. These areas may see some improvement through the rest of this afternoon while light easterly surface winds across the north-central MT plains will maintain widespread low clouds/stratus along with some lingering areas of fog. Areas of fog will redevelop/expand again tonight across the plains while increasing mid-high level clouds may prevent widespread fog development overnight across southwest MT. A more southerly flow aloft develops tonight ahead of an upper level trough offshore of the Pacific NW with a few light showers potentially tracking north into portions of SW MT and along the Continental Divide after midnight.

Additional showers track northward into primarily areas near the ID border through much of the day tomorrow as the offshore trough elongates and shifts inland. More widespread precipitation develops late Saturday night through Sunday as the trough axis shifts east across the Rockies. The bulk of the energy tracks south of the area with highest precip amounts expected across eastern portions of southwest MT while a more brief period of precipitation shifts across central/north-central MT, mainly late Sunday, before the trough and associated precipitation shift east of the area on Monday. Snow levels are initially above 7000 ft with models continuing to trend slower with the arrival of cooling aloft and lowering snow levels on Sunday, limiting impactful snowfall to areas mainly above passes through much of the weekend.

Upper level ridging rebuilds early next week, but may be transient with most model ensembles showing some form of undercutting energy tracking east from the Pacific and inland by Wednesday. Temperatures should rebound to closer to average for at least the first part of next week. Hoenisch

- Forecast Confidence & Scenarios:

Areas of dense fog are likely again tonight with with the easterly/light-upslope flow supporting the highest risk (60-80%) for visibility of 1/4 mile or less along areas adjacent to the east slopes of the Rocky Mtn Front and Judith/Snowy Ranges. The influx of mid-high level cloud cover from The south later tonight may help mitigate a greater coverage of dense fog across north-central MT.

Temperatures in the mid-upper 30s across the north-central MT plains will fall to near or slightly below freezing again tonight, bringing some risk for localized icing of elevated surfaces, especially in areas where fog is most dense and may support freezing drizzle. The shallow cool airmass continues to erode Saturday and Sunday, but a few isolated locations may hold onto the colder air as precipitation arrives Saturday night Sunday creating some potential for light freezing rain/drizzle.

The risk for snow accumulation in excess of 2 inches late this weekend is highest at elevations above 7000 ft but only around 20% or less for most passes at or below 7000 ft. Hoenisch

Aviation

30/18Z TAF Period

Continued LIFR and IFR conditions for the northern tier terminals as well as KBZN with low stratus, patchy fog, and mist. Localized areas of freezing drizzle is possible today and into tomorrow morning for Central MT north of KLWT and North Central MT along the Rocky Mountain Front. Primary hazards will be moderate icing and widespread visibility restrictions and mountain obscurations. MVFR to VFR conditions are expected to return tomorrow after 18Z for most terminals. - Akins

Preliminary point temps/pops

GTF 30 50 35 44 / 0 20 10 70 CTB 27 50 29 45 / 20 0 20 60 HLN 31 50 35 45 / 0 20 20 80 BZN 31 47 33 43 / 10 40 10 60 WYS 28 43 28 40 / 70 80 70 100 DLN 35 48 37 42 / 20 60 60 90 HVR 26 47 29 50 / 0 10 10 10 LWT 27 48 33 52 / 0 20 0 20

Watches, warnings and advisories

None.