Avalanche Forecast

A break between weather systems should be seen on Thursday. Sun is most likely in the Olympics, the south Cascades and east of the crest but watch for solar effects in all areas.

Recent winds have been mostly S-SW so firmer wind slab should be found mainly on NW-SE slopes. But there have been winds from other directions lately such as local east winds on Monday so watch for firmer wind transported snow on all aspects, especially in areas of complex terrain.

Watch for solar effects in all areas especially in areas where there has been more than a few inches of snowfall the past couple days. Solar effects should make loose wet avalanches possible mainly on solar slopes in all the terrain bands but keep an eye out on all aspects. Watch for surface wet snow deeper than a few inches, pinwheels and increasing natural releases.

You need to avoid areas on ridges where there may be a cornice and slopes below cornices! Natural cornice releases and resulting slab avalanches are unpredictable and as seen above in the special note cornices have triggered major slab avalanches lately. This avalanche in the special note above narrowly missed multiple parties and easily could have been a major avalanche accident!

See a blog post regarding cornices here.

 Although not listed as an avalanche problem watch for storm slab if you are in an area that has had more than a few inches of rapidly accumulating snowfall.

Increasing alpine winds, increasing clouds, and increasing rain or snow should be seen Thursday evening as the next front begins to move into the Northwest.

Weather and Snowpack

Special note:

A major load has been placed on our snowpack over the past two weeks especially in the north Cascades. This has resulted in many very large avalanches and a few very large to historic avalanches. For example, from March 9-19, Mt Baker received nearly 15 inches of water equivalent! In large terrain, above 7000 feet, much or all of this fell as snow and with very strong winds. Be aware we have a problem of low probability but very high consequence avalanches, which cannot be predicted, which may be with us for some time this spring. Most recently:

 Deep hard slab triggered by a massive natural cornice failure on Ruby Mountain, Sunday afternoon, 3-19. Photo via the NWAC Observations page.

The first week or so of March was very cool and snowy. NWAC stations along the west slopes of the Cascades piled up about 3 to 8 ft of snow with the most at Mt Baker.

The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately, these systems delivered far more rain than snow. At least two regional avalanche cycles occurred during the stretch. Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. 

Another strong low pressure system brought several inches of rain to the west slopes of the Cascades outside the Cascade Passes Friday 3/17. 2.5 to 4 inches of water was seen at Paradise, Crystal and Mt. Baker, respectively, over the 24 hours ending saturday morning, mainly in the form of rain. Stevens and Snoqualmie Pass, picked up 6-8 inches of new snow Friday night before changing to rain later Saturday morning.

Rapid cooling with the frontal passage produced about 8 inches of snow at Mt. Baker and in a convergence band which set up in the North Central Cascades with decreasing amounts seen elsewhere along the west slopes of the Cascades Saturday morning to Saturday evening (Stevens - <5", Snoqualmie 4", Crystal <3").

Weaker fronts crossed the Northwest on Tuesday and Wednesday. This will be continuing to cause snow mainly in the above treeline areas. 2 day snowfall ending Thursday morning should be 10 or more inches in the above treeline at Mt Baker with perhaps about 5 inches above treeline along the rest of the Cascade west slopes.

Recent Observations

North

NWAC observer Lee Lazzara was in the Ptarmigan Ridge area of the Mt Baker backcountry Sunday.  There was widespread evidence of the most recent wet snow avalanche cycle from Friday night with debris at the bottom of many avalanche paths. Crowns from wet slabs were especially large below treeline. Lee found the most recent rain crust very supportable above treeline, but still in the process of re-freezing below 4500 feet. Small loose wet slides released naturally and ran well on steeper solar slopes during clearing in the afternoon.  About 20 cm (8") of recent storm snow was evenly distributed regardless of elevation. Isolated pockets of shallow wind slab were found above treeline, but no obvious loading pattern was discernable. 

The massive natural cornice triggered avalanche in the photo above was on the north side of Ruby Mountain on Sunday, ran over ~1400' vertically, and a far greater distance laterally. The crown was just below ridge-crest and varied in height from 7-25 ft. This avalanche narrowly missed multiple parties and easily could have been a major avalanche accident! See the link to the observation in special note above.

Central

The Alpental patrol reported easy and widespread ski triggered 6-8 in storm slabs on the upper half of Alpental Saturday morning with rain reaching the summit. Loose wet avalanches were easily triggered later in the day on steeper slopes. The Stevens Pass patrol had similar results Saturday morning with widespread sensitive, loose wet slides, up to size 2, natural and human triggered during the warming and switch to rain. Stevens Pass reported no new avalanche activity as of Monday morning.

The Alpental patrol on Monday indicated about 6 inches of recent snow was becoming wet with rain showers or heavy wet snow by the afternoon and was becoming reactive to pushing with skis on steeper slopes, releasing good sized loose-wet slides.

NWAC forecasters on Denny Mountain, at Alpental Tuesday at about 5000 ft found about 8 inches of moist recent snow over the thick strong rain crust from Saturday 3/18.

The Alpental patrol on Wednesday reports about 2 additional inches of new moist or wet snow on the thick crust with triggered loose wet avalanches remaining possible.

South

The Crystal patrol reported a natural cycle Friday night, presumably loose wet, but little to no results during avalanche control work Saturday morning. On Sunday they reported a stout rain crust on the upper mountain with about 5-8 cm (2-3 in.) of well bonded snow on top of the crust.