Avalanche Forecast

Generally light rain and snow should glance the north Cascades and Olympics with very little precipitation expected further south of these areas Tuesday. There may be a few sunbreaks in the late morning and midday before clouds thicken.  New loading and wind transport is not expected to play a role in the avalanche danger Tuesday.  

A modest warming Tuesday afternoon should lead to minor loose wet concerns on all aspects, especially in the central and southern WA Cascades near and below treeline. Watch for loose wet concerns in the afternoon.  Small point releases on steeper slopes have a fair bit of new and consolidated snow to entrain and would be the most problematic around terrain traps.  Storm slab avalanches should be unlikely given the generally good reports of bonding to the old snow surface and have been removed as a primary concern. 

Generally soft wind slab at higher elevations may still be sensitive, and we advise the most caution when traveling at higher and more open avalanche terrain that may be wind loaded and where colder temperatures should preserve lingering instabilities.  Watch for cracking in the snow surface and for signs of obvious wind transport such as scoured lee ridges. Be aware that locally the soft wind slab concern may extend into the near treeline zone. 

Recent Weather Summary

Following the active weather over the past month or so we are shifting avalanche concerns to more storm related instabilities and moving away from mid-season deeper snowpack concerns at least for the short term.

A stalled and moist frontal boundary draped over mainly the north WA Cascades Saturday afternoon finally sagged south on Sunday, with rain changing to snow generally in a north to south fashion across the area.  A favorable temperature trend occurred with this storm, with gradual cooling from Saturday night through Sunday night.   From Saturday night through Monday morning NWAC sites along the west slopes picked up 8-18 inches of snow, with more at higher elevations that cooled first.   Generally light showers at cool snow levels were seen through the day Monday, but moderate NW winds at crest level transported snow Sunday night and continued into Monday. 

Recent snowpack and avalanche observations

New avalanche reports were limited to small wet loose releases Saturday and Sunday during periods of warming and light rain.  Most ski areas and DOT on Sunday through Monday morning reported generally good bonding of the new storm snow with blowing and drifting of the most recent lower density snow.  Over the weekend, NWAC observer Dallas Glass reported very moist snow from last week's warm temperatures and rain had penetrated over a meter deep in the Paradise area of MRNP. This corresponds to a pit from WSDOT professionals mid-mountain on Alpental last week that showed wet snow and a lack of temperature gradient in the upper and mid snowpack. The new snow is insulating this warm portion of the snowpack...so expect moist or wet snow to still be found for beneath the most recent storm snow and near surface melt freeze crust. 

However, moderate NW winds and cold snow available for transport at upper elevations likely continued to build new wind slab on Monday. Crystal mountain ski patrol reported wind slab of 6-8" during Monday control work on lee easterly aspects, but not especially sensitive to ski triggering.  NWAC observer Jeff Hambelton in the Mt. Baker area found stiffer storm snow bonding poorly to earlier storm snow over the weekend and a light freezing rain crust below 5000 feet. He observed some cracking between these storm layers and one small natural slab avalanche. Cold temperatures and limited sunshine should help preserve wind slab concerns on Tuesday at higher elevations on lee slopes.  Good lower density snow (powder) should be found on non wind affected terrain. 

Notable avalanche activity from last week 

The ski patrol at Crystal Mountain on Sunday and Monday of last week produced consistent large wet slab releases with large explosive charges releasing to deep layers from early this winter. These avalanches were generally on N to E slopes at about 6-7000 ft with crowns of 4 to 6 feet and up to 10 feet in spots with the High Campbell chair and some trees destroyed.  

On Tuesday, March 11th, Dallas Glass also found recent very large wet slab releases on Kendall Peak at Snoqualmie Pass. Several large to very large wet slab avalanches began at about the 5500 ft elevation on primarily steep W aspects. These slides likely released a week ago Sunday night or Monday with heavy rain. On Thursday, backcountry skier Andy Hill found wet slab debris likely from the same period that stepped down to the firm January crust in Great Scott Bowl in the Alpental backcountry. Also following the rain event two weekends ago, avalanche educator Gary Brill reported about a dozen large slab releases on N thru E aspects up to around 6000 ft on a flight last Wednesday along the west slopes.  

With the recent cooling trend, it has become more unlikely deep wet slab avalanches could be human or naturally triggered without an extremely large load (i.e. explosives or serac fall seen at MRNP last week). Wet slabs could again become an avalanche concern during extended stretches of rain and/or warm temperatures and are not necessarily tied to the period of heaviest rain or warmest temperatures.

  

Photos by Andy Hill 3-11-14, Alpental backcountry off a D3/R3 wet slab from early last week.