Likelihood ?CertainVery LikelyLikelyPossible
Size ?HistoricVery LargeLarge
We have a well developed layer of surface hoar out there that can be found on shady aspects above 5,000' in elevation. In the Purcells I was finding it about 8" below the surface, in the West Cabinets there are two layers being found in the upper 18" of the snowpack. In the East Cabinets I can't find any, despite a lot of looking for it! It is gaining strength and is showing a low likelihood of propagating into an avalanche at this time; however, I wouldn't fully trust it just yet. Your likely spots to have trouble are very steep openings or convex rolls in the timber where the surface hoar was preserved prior to the last snowfall. There are also some weak sugar layers above and below the February 1st rain crust in the Purcell Range that I would continue to keep in mind, These layers are also trending towards a more stable state as the mild temperatures heal the snowpack.
The weather has been pretty mild lately, and that has been good for creating a stable snowpack. Overall things are looking pretty good out there. Most of the terrain I have been on this week is pretty firm on the surface, wind buff, breakable crust and the occasional powder pocket in well protected timber. As I mentioned above we have a weak layer that is very pronounced under our last snowfall. If you dig down into the snow on shady aspects in the timber you will possibley find a thin grey streak in the upper snowpack. This layer of surface hoar was found Monday at Flatiron and the flakes were 8mm tall, buried 7-8" below the surface. My cohorts on the Idaho side of the West Cabinets are finding two layers of surface hoar buried in the upper 18" of the snowpack. I spent a fair bit of time poking around shady aspects in the Cabinet Wilderness and was unable to find any buried surface hoar in that location. Stability tests show this layer is resistant to propagation and continuing to gain strength. Keep your hackles raised if you are riding in steep timber on northerly aspects until this layer is fully healed. In terrain that has been exposed to the wind and sun, this surface hoar was likely destroyed before it had the chance to become a problem, if you are looking to play in steeper terrain then these south and westerly aspects will be safer choices right now.
Going into the weekend we have 4-9" inches of snow predicted at the upper elevation bands. This snow will likely come in on the dense and heavy side. It will also be falling on some surfaces that will be difficult to stick to, such as wind crusts and graupel. Keep on your toes Saturday and Sunday as this new snow come in. Weakness will be easy to spot on the surface of the snowpack. If you observe fresh avalanhces or cracking in steep terrain then it is time to dial back your terrain selection to more conservative ground.
Backcountry Forecast from NWS Missoula issued: 400 AM MST Fri Mar 6 2020 DISCUSSION: Northwest Montana: It will be warmer than average today and there could be a passing shower or sprinkle in the mountains. Spotty areas of steady precipitation is expected to develop later this evening and tonight with the snow level around 5,000 feet. A cold front will move through by Saturday afternoon, which will reinvigorate mountain snow showers that will linger into Sunday. Confidence is low, but a few week disturbances could trigger more snow showers on Monday. Daytime highs will generally be near average while clearing at night will allow good cooling.
Kootenai: --------------------------- 5000-7000 FT ---------------------------- Today Tonight Sat Cloud Cover 90% 95% 100% Hi/Lo Temps 33 to 41 27 to 32 29 to 36 Winds(mph) SW 11G26 SW 8G23 SW 9G22 Precip Chc 40 90 100 Precip Type snow sno/fzra snow Liquid Amt 0.01 0.25 0.36 Snow Ratio(SLR) 10:1 13:1 13:1 Snow Amt(in) 0 3-4 4-5 Snow Level 4500 4500 4000
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