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RegisterDec 26th, 2019–Dec 27th, 2019
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Brisk winds and perhaps an inch or two of snow will build fresh slabs that may be easy to trigger. Look for signs of wind transported snow and avoid steep, wind loaded slopes. Any small avalanche near the surface may step down to a weak layer near the ground. If triggered, this avalanche would be a different animal.
A weak cold front should give us a few inches of new snow and some wind, and this will bump the avalanche danger up for Thursday. Recently, the cold temperatures have substantially weakened snow surfaces, and widespread surface hoar has been observed growing in the area. It has been a number of days now since the big storm event last weekend, and the last reported avalanche and instabilities on a weak layer near the ground have been on the 23rd. A near surface crust can be found up to around 5,500ft throughout much of the zone, making travel difficult at these lower elevations. It is also very unlikely you'll trigger avalanches at these lower elevations because of refrozen conditions. Have a look at the new Regional Synopsis for a look back at our recent wet and wild past.
More remnants of last weekends avalanche cycle: East Face of Mt. Mastiff, E at 6,600ft from Hwy 2. December 26, 2019. Photo: Matt Primomo
December 26, 2019 (The regional synopsis is updated every Thursday @ 6 pm)
No matter where you are in the northwest, the snowpack looks a world different than it did a week ago. A major storm, widespread avalanches, developing weak layers, and an initially thin snowpack made for a hectic week. Let’s take a look at a few large scale trends for our holiday season.
A very large natural avalanche (D3) on the Shuksan Arm near Mt Baker that occurred during the storm cycle. Photo: Adam U.
Wet and Wild
“Some of the highest precipitation rates I’ve ever seen.” “Absolutely puking!” “Rivers running in the streets.” “Snowing snow hard I can’t see my hand in front of my face.” These were all statements we heard describing the wet and wild storm that impacted the Northwest from about Thursday (12/19) through Sunday night (12/22). Water totals were staggering in many locations (Table 1). For Hurricane Ridge, Mt Baker, Washington Pass, and high elevation terrain this deluge translated into significant snowfall. However, warm air in the central and southern parts of the region brought rain well into the near treeline bands. Whether your favorite spot saw rain or snow, four things are clear. 1. This was a huge loading event. 2. A widespread natural and triggered avalanche cycle (up to D3) occurred. 3. Avalanche danger spiked during and just after the storm before trending down through the week. 4. The snowpack changed dramatically.
Location
Precipitation 12/19-22
Hurricane Ridge
4.97”
Mt Baker Ski Area
7.35”
Washington Pass
3.53”
Stevens Pass
6.28”
Leavenworth
2.94”
Snoqualmie Pass
7.89”
Crystal Mt Ski Area
7.45”
Paradise, Mt Rainier
6.57”
Mt Hood Meadows
2.18”
Table 1: Precipitation totals for select weather station locations December 19-22.
The Emergence of Persistent Slab Avalanche Problems
Coming out of this huge loading event, there was hope that many of the early season weak layers had been destroyed. Unfortunately, this was not the case in some locations. Old weak snow layers reared their heads in areas east of the Cascade Crest and near Crystal Mountain. While the exact extent and character of these layers can differ slightly, most locations are finding a layer of weak sugary facets associated with a crust about a foot above the ground. Persistent slabs are tricky to assess. Do not solely rely on snowpits and snowpack tests to help you choose terrain. How will these layers change going forward? Only time and observations will tell.
You may find weak sugary facets near a crust about 12 inches above the ground similar to what you see here. Photo: Jesse Charles
Low Tide Snowpacks During the Holidays
The storm this past week definitely helped the meager early-season snowpacks in all locations. Areas like Hurricane Ridge, Mt Baker, and Washington Pass experienced a jump of 20 or more inches in their snow depths over the past week. However, even with these increases, an early season snowpack still describes most locations. Expect numerous obstacles as you travel including open creeks, rocks, and trees. With this thin snowpack, limited access, and difficult travel we still have limited observations in some regions.
Open, deeply incised creeks in the Alpental Valley. Photo: Dallas Glass
Lack of information leads to a higher than normal degree of uncertainty. If you travel to higher elevations or more remote trailheads, recognize you could experience different conditions than the forecast suggested. You can help us fill in the gaps by submitting your observation here.
Happy Holidays!
-Dallas Glass