Avalanche Forecast
Regions: Snoqualmie Pass.
You may experience higher avalanche danger as you ascend in elevation into areas where more snow fell during recent storms. Identify and avoid steep slopes where you find pillow-like drifts, fresh cornices, or blowing snow. Due to recent strong winds, you could find these clues well below ridgeline and on the sides of mid-slope features.
Discussion
Expect the avalanche danger to increase as you ascend into areas where more snow accumulated. Any instability should be limited to the upper snowpack above a prominent crust formed on Friday due to rain and warm weather. This crust can act as a clear marker for your observations.Â
Even though the calendar says January, the low elevations are still not filled in with snow. Expect challenging travel, with numerous open creeks and obstacles to navigate.
Snowpack Discussion
Happy New Year!Â
The pacific northwest rung in the new year with a winter storm cycle that brought changing conditions to our region. This storm exhibited three characteristics: warm, wet, and windy. Let’s take a look at the end of 2019, the beginning of 2020, and where we can go from here.Â
Wrapping up 2019
The last few days of December were generally quiet and cold. The snowpack seemed to enjoy this break in the weather. Lingering unstable snow from the pre-Christmas storms gained strength, persistent weak layers appeared to stabilize, and avalanche hazard decreased in all forecast zones. All in all 2019 ended quiet and uneventful… until the New Year’s Eve weather party showed up … Â
Quiet weather led to lower avalanche danger during the last week of 2019. Hogsback, White Pass, WA. Photo: Andy Harrington
Blowing into 2020
A warm, wet, and windy weather system blew into the northwest for New Year’s Eve and New Year’s Day. This brought rapidly changing conditions and increasing avalanche hazard to all areas.Â
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Warm: Unfortunately this system brought with it warm air. Freezing levels measured near the coast reached 9000’ on the afternoon of the 31st. Many weather stations recorded above freezing temperatures during the onset of precipitation.Â
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Wet: While this system wasn’t as wet as the atmospheric river prior to Christmas, it still produced impressive water numbers in many areas. The bulk of the precipitation seemed to be focused on the Passes and Volcanoes, and water spilled over the crest to places like Washington Pass and Leavenworth. Sadly, when combined with the warm temperatures, this translated to rain well into the near treeline band (or higher) for most areas. The main exception appeared to be in the northeastern cascades, where locations like Washington Pass remained all snow.Â
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HurRidge
MtBaker
WaPass
Stevens
Leavenworth
SnoqPass
MtRainier
MtHood
Precipitation (in)
1.84
3.39
1.42
4.56
1.06
6.19
5.39
5.41
Snow (in)
-
15
-
12
0
3
10
8
Table 1: Precipitation and storm totals from selected weather stations during the New Year’s Eve Storm. “-†24hr storm snow not measured.Â
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Windy: While the warm and wet were impressive, it’s the winds that may set this storm apart. Most weather stations recorded very strong and extreme winds during the storm. Alpental exceeded 100mph just after midnight to ring in the new year. Any dry snow at high elevations was redistributed by the wind and snow surfaces were transformed.Â
Table 2: Wind speeds from New Year’s Eve from selected wind sites. Note the sustained period of winds between 40-60mph.
Eventually, temperatures cooled, the rain turned back to snow, and winds calmed. Many locations picked up additional snow as the storm wound down, but 2020 was already off and rolling with its first major storm.
New Year’s Resolutions
The active weather pattern that started the new year appears to continue. The snowpack and avalanche conditions will continue to change. So, what can your New Year Avalanche Resolutions be?Â
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Read the forecast. This is a great way to monitor conditions even if you aren’t heading into the mountains.Â
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Get out in the snow! Enjoy the wonderful mountains in your backyard.Â
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Submit an observation. Tell the avalanche center what you saw while out in the snow by submitting an observation and sending in a photo.Â
Thanks for all of your support in 2019 and here’s to 2020!
-Dallas
Â
Avalanche Problems
Wind Slabs
Keep your eyes open for signs of wind loading such as snowdrifts, textured snow surfaces, fresh cornices, and blowing snow. You may find these observations in areas well below ridge crest and along the sides of mid-slope features. Stop, identify, and steer around any slope greater than 35 degrees where you suspect wind loading occurred. Potential avalanches will be larger and more difficult to manage as you move into higher and more exposed terrain.
At lower elevations, we don’t expect enough new snow to pose a hazard. As more snow accumulates, you may trigger small loose dry avalanches in the unconsolidated snow.
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1