Avalanche Forecast

Additional showers, mostly light to occasionally moderate, should persist Tuesday night through Wednesday. Significant cooling is expected through the day Wednesday.

The cooling Wednesday should allow for an overall decreasing danger. Previous moist to wet shallow surface snow should begin re-freezing and strengthening.

Only shallow snow from a few inches up to about 8-10 inches overlies the strong rain crust from 3/18 in most areas, mostly depending upon elevation and recent precipitation amounts.

Moderate winds and showers at lowering snow levels should build some shallow fresh wind slabs at higher terrain along ridges, mainly on NW-NE-E facing terrain. Watch for firmer wind transported snow on all aspects, especially in areas of complex terrain. 

At lower elevations, gradually re-freezing surface snow will form a new strengthening crust by later Wednesday. 

It is always a good plan to travel well back from ridges, suspected of cornice formation, or on steep slopes below cornices.

Additionally, we have seen large cornice-fall avalanches that could trigger potentially very large wind-slabs formed during the last storm cycle or as new snow is added.

Weather and Snowpack

Special note:

The amount of recent load that has been placed on our snowpack over the past two weeks is very significant. 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 may have this problem of very high consequence avalanches, but low probability of trigger, 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 from recent observation posted at NWAC

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. 

After a short respite from the active weather pattern on Thursday, another strong low pressure system brought several inches of rain to the west slopes of the Cascades outside the Cascade Passes Friday night. 2.5 to 4 inches of water was seen at Paradise, Crystal and Mt. Baker, respectively, over the 24 hours ending at 5 PM PDT Saturday, 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 late Saturday morning through Saturday evening (Stevens - <5", Snoqualmie 4", Crystal <3"). Sunday was cool with light winds with a general clearing trend seen throughout the Cascades. 

Light to moderate showers with mild temperatures Monday and Tuesday caused rain at mid and lower elevations and a few up to several inches of heavy wet snow near and above treeline.

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. 

A massive and destructive size 3.5+ natural avalanche was witnessed on the leeward upper alpine zone of Ruby yesterday. The slide was triggered by a large, natural cornice fall and 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. Link to the observation in special note above.

Central

Alpental pro-patrol reported easy and widespread ski triggered 6-8" 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. Stevens Pass pro-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.

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

South

Crystal patrol reported a natural cycle Friday night, presumably loose wet, but little to no results during avalanche control work Saturday morning.  On Sunday, Crystal pro-patrol 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.