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. While the east slope zones may not have had as much recent water equivalent as Mt Baker in the west, a greater percentage of precipitation fell as snow, due to cooler air mass. 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 and NRCS stations indicate about 2 feet of snow in the northeast Cascades with less elsewhere along the Cascade east slopes. 

The 2nd week of March was equally active with non-stop Pacific frontal systems pummeling the PNW. Unfortunately, these systems delivered more rain than snow. At least two regional avalanche cycles occurred during the stretch. The most recent cycle from earlier in the week had many massive slides that covered Hwy 20 near Washington Pass up to 40' deep in places! Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. Far less precipitation was seen further east of the crest during this period for areas like Blewett Pass and Mission Ridge. 

After a short respite from the active weather pattern on Thursday, another strong low pressure system brought 6-12+ inches of snow to the northeast and central-east slopes of the Cascades Friday night and mostly rain for the southeast Cascades. This was followed by snow levels rising to 6000-6500 feet in the northeast and central-east Cascades and likely 7000 feet in the southeast Cascades by early Saturday morning.  Rapid cooling began mid-day Saturday. Strong W-SW winds were likely transporting new snow above treeline by mid-day Saturday. 

Sunday through Monday was cool with light winds with a general clearing trend seen throughout the Cascades through early Monday with high clouds late.  

Recent Observations

North

The North Cascades Heli Guides were near Silver Star on Thursday 3/16 reported many previous natural storm slab avalanches up to size 3, likely releasing midweek. They also reported several small triggered storm slab avalanches. This activity was on N-NW slopes in the 8000 ft range.

More observations from Friday in this zone indicated a significant distinction in the recent storm snow with elevation, with up to 4 more inches of storm snow above about 6500 feet. The several recent warm precipitation events this week appear to have limited the upper elevations of rain to about 6500 feet. At elevations up to 8000 feet, the recent precipitation has fallen as snow. In these higher elevations, some shallow triggered storm slab avalanches have been noted over the past few days.

On Sunday, the NCH operation was in the Silver Star and Varden Creek drainages and found evidence of recent storm slab releases in unsupported steeper terrain mainly above treeline, but that recent storm slabs were becoming less sensitive to human triggering.

Guides near Washington Pass Tuesday, 3/21 reported hearing many natural avalanches near midday following a prolonged sunbreak and subsequent brief warm up. Numerous avalanches were likely small, however, some avalanches sounded much larger, likely involving deeper layers below the relatively shallow recent storm snow.  

Central

NWAC observer Jeff Ward was in the Cle Elum drainage on Mt Hawkins and Red Mountain up to about 6000 ft on Thursday 3/16 and noted evidence of an impressive avalanche cycle the past couple days. The current conditions were 3 cm of new snow over 3-7 cm thick, firm crust with recent rain penetration to about 40 cm in the snowpack. The Valentine's Day crust was found at 90 cm but tests did not give results.

NWAC observer Tom Curtis was at Blewett on Diamond Head up to about 5500 ft on on Thursday 3/16 where there were no recent avalanches just consolidation. SW-W-NW slopes were scoured, with a breakable or supportive crust elsewhere over moist 1F or P rounded crystals down to the ground. He found some reactivity in a layer at about 50 cm down, which should not be a current problem, but might have contributed to avalanches a week ago.

Mission Ridge pro-patrol reported a well-behaved springlike snowpack in their area with no avalanche problems noted over the weekend. 

South

No recent observations.