Avalanche Forecast
Regions: Olympics.
Shallow wind slabs may exist on lee slopes above treeline while generally safe conditions are expected at lower and mid elevations. Steer clear of slopes that still have large overhanging cornices. Pay attention to changing conditions if an incoming storm arrives earlier than anticipated on Friday.
Discussion
NWAC and NPS professionals found a shallow amount of wet snow (4-7â) above the stout 2/1 crust in the Hurricane Ridge area on Thursday with a rain/snow mix just above 5200' and a cold rain below.Â
Earlier in the week during the warmer part of the storm cycle, rain and warm temperatures had caused an avalanche cycle. Evidence of loose wet and shallow slab avalanches was easy to find throughout the terrain, even with poor visibility. Enough water had entered the snowpack above 5000â to cause the 20th of June glide crack to widen since last weekend.Â
Cornices had also broken off in places, with large pieces found on the slopes below. While cornices were sagging and arenât as likely to fail, continue to keep your distance while traveling along ridgelines and especially while crossing on slopes below these dense hard chunks of snow. Â
In isolated areas, you may still trigger a small loose wet avalanche at mid and lower elevations on very steep slopes. You'll need to weigh the consequences of even a small loose wet avalanche near terrain traps like gullies, cliff bands, or open creeks.
This photo sums up the last few days;Â cornice releases, shallow slabs, shallow loose wet debris, and an opening glide crack. 5300 ft, NE aspect.
Feb 6th, 2020 Photo Robert Hahn
Snowpack Discussion
February 6, 2020 (The regional synopsis is updated every Thursday @ 6 pm)
If we could choose one word to sum up the last week, and possibly 2020 in general, that word would be fluid. As of February 6, we are in the midst of yet another atmospheric river event, bringing large amounts of low elevation rain and high elevation snow to our region. The WSDOT-SCR avalanche team relayed that this past January has been the wettest on record at Snoqualmie Pass since precipitation records started in the 80s, and itâs their second wettest month on record. With such potent storms, itâs no surprise that our snowpack and avalanche danger has also been fluid, with fluctuations between high and low danger over short time periods.Â
February began on the tail end of our largest rain and wind event of the season, with many NWAC weather stations recording wind gusts of over 100 mph and impressive water numbers as high as almost 10 inches in a 48 hour timeframe.Â
Maximum wind gusts from weather stations in the NWAC Network Friday 1/31 into Saturday 2/1
This event had freezing levels surge to around 8000 feet across the region, introducing rain to a cold dry snowpack at upper elevations for the first time this season. This included rain above 7000 feet in the Washington Pass area, which had largely escaped the wrath of warmer storms up to this point. Dangerous avalanche conditions during this period produced widespread wet avalanches in most zones as large as D3. Along with Loose Wet and Wet Slab avalanches, Cornices failed naturally, and Glide avalanches were observed in multiple zones. Â
Natural glide avalanche (D2) that occurred on a SE aspect at 4400ft on a convex rock slab between Schriebers Meadow and the Railroad Grade. 02/02/20 Photo: Andrew Kiefer
As the rain finally subsided, cold air flooded our region, allowing the wet snow surface to begin to freeze from the top down. This sharp cooldown created what we are calling the 2/1 crust and allowed for Low danger across the region for a few days. The 2/1 crust varies in thickness but should exist in all areas of the region below ~8000 feet and may be considered as our ânew groundâ. During this period of low danger, most zones picked up modest amounts of low-density snow to overlay the 2/1 crust and even had a bit of sunshine.
Unfortunately, the period of low danger was short-lived, when two days later, another atmospheric river was on our doorstep. This time, the event started off cooler and had lower projected freezing levels. Many zones in the region were able to pick up a foot or more of new snow in all elevation bands before a switch to rain, with upper elevations receiving multiple feet of snow, creating what we are referring to as the 2/4 interface. The setup of heavy fresh snow over the low-density snow sitting on the 2/1 crust was a great recipe for avalanches on its own. Throw in the switch to rain at low and mid-elevations along with high winds and precip rates, and very dangerous avalanche conditions developed across the map on Wednesday the 5th.
This is where we find ourselves on Thursday, in the middle of a notable avalanche cycle producing wet snow avalanches below the rain line with dry snow avalanches above. The way this winter has been going so far, itâs a good guess that things will continue to be fluid going forward, letâs just hope itâs a colder type of fluid.
Loose Wet avalanche activity on Snoqualmie Pass. 02/05/20. Photo: Andy Harrington
Avalanche Problems
Wind Slabs
Shallow wind slabs may exist on lee slopes above treeline. With no recent observations from higher elevations, you’ll need to approach slopes steeper than 35 degrees with wind drifted snow cautiously, feeling for hollow or denser snow on top of the most recent crust. If the most recent crust remains firm and icy above treeline, even a small avalanche could take you on a long unpleasant ride.
An incoming storm on Friday will cause increasing winds and mid and high elevation snow during the afternoon. If the storm arrives quicker than forecast, pay attention to changing conditions and be prepared to dial back your plans.
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.
Likelihood: Possible
Expected Size: 1 - 1