Avalanche Forecast
Regions: Cascades - North West.
Additional snow and wind over the next 24 hours will maintain dangerous avalanche conditions. You can trigger large avalanches within new snow on slopes 35 degrees and steeper. The most dangerous conditions exist in wind-loaded areas where you will find thicker and more reactive slabs.
Discussion
On Saturday, the Mt. Baker Ski Patrol reported several explosive and skier triggered slab avalanches (D2). Avalanches failed within new snow layers 1-2ft deep and were especially reactive in wind loaded areas. Evidence of extreme winds (90mph gusts recorded at Pan Dome) was easy to find with fresh wind drifts on leeward slopes, and some windward slopes scoured down to firm old snow surfaces. Since Friday night, the Mt. Baker area received 12-18in of new snow above 4000ft. Snow levels should remain near 2000ft as snowfall continues with the heaviest precipitation expected Sunday afternoon.
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
-
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
-
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
Â
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
-
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
-
Read the forecast. This is a great way to monitor conditions even if you aren’t heading into the mountains.Â
-
Get out in the snow! Enjoy the wonderful mountains in your backyard.Â
-
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
Storm Slabs
Storm slabs will grow in size and distribution as the day progresses, and will be easiest to trigger in the afternoon when precipitation rates increase. Keep loose dry avalanche concerns in mind as well. These slides could knock you off your feet and entrain quite a bit of snow as they run downslope. Steer around slopes 35 degrees and steeper, and avoid exposure to overhead hazard. Carefully assess new storm snow layers as you travel. Watch for obvious signs of unstable snow like cracking, collapsing, and fresh avalanches. Use small, inconsequential test slopes to check how easily the snow may fracture and slide. Choose conservative terrain, and give the new snow time to stabilize.
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1