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RegisterMar 4th, 2017–Mar 5th, 2017
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Gradual improvement in avalanche danger Sunday. However, large human triggered avalanches remain likely. Storm slabs will heal slowly and large wind slabs will be sensitive to trigger.
Given the recent active avalanche conditions, the main emphasis is to step back and give this significant storm snow additional time to heal and stabilize.
Dangerous avalanche conditions are expected to gradually improve, however Careful snowpack evaluation and cautious routefinding will be essential Sunday.
Light to moderate snow showers at cool temperatures are expected overnight and early Sunday before tapering through the day. Winds should be light, except light to moderate in the alpine.
Only light accumulations of new snow are expected and with cold temperatures and light winds this should not affect the current avalanche danger significantly.
Recent moderate to strong S-SW winds will make wind slab most likely on northwest to southeast slopes, but keep an eye out on all aspects in areas of more complex terrain. Watch for firmer wind transported snow from Friday and possible deeper wind transported layers. Older wind slabs may be masked by the recent fresh snow.
Cornices won't be listed as an avalanche problem in this area, but avoid travel on ridges, where recent cornices may have formed and avoid slopes below cornices.
Weather and Snowpack
The most recent wet warm storm arrived on Valentines Day 2/14 and formed the uppermost strong rain crust in our snowpack in the Central East and Southeast Cascades while only a thin freezing rain crust was observed in the Washington Pass area.
A series of disturbances in cool, NW flow aloft from Saturday 2/25 through Tuesday 2/28 deposited 2-16 inches snow along the east slopes of the Cascades. Very strong alpine west winds were seen in most of the Olympics and Cascades on Tuesday.
Southwest flow aloft began to ramp up again on Thursday as the first in a new series of fronts crossed the Northwest. Strong southwest flow carried a second stronger front across the Northwest on Friday evening. Along the Cascade east slopes this caused strong southwest alpine winds and heavier moist or denser new snow above about 3-4000 ft and wet snow or rain below about 3-4000 ft.
Not a good time to be without the Washington Pass precipitation and snowdepth site, we are hopeful to get that back online by mid-March. As such, we are unsure just how much recent storm snow has fallen over the past few days in this zone, though Harts Pass has received over 1 foot and likely 1.5 ft or more since Thursday.
Recent Observations
North
A report from the NC Heli Guides indicates a cycle of natural and ski triggered wind slab avalanches during the wind event on Tuesday and Wednesday 2/28-3/1. About 50-80 cm of storm snow was found with a good bond to the Valentine's Day crust. About 20-30 cm of recent snow was covering about 10 cm of wind slab in some areas.
A party of four skiing at Washington Pass near the highway hairpin on the east side of the pass was hit by a natural cornice released avalanche on Tuesday afternoon. Four people were caught and carried up to 1000 ft downslope. Fortunately, there were no fatalities and no full burials but there were apparently some injuries. The release occurred on a very steep slope at the top of a northeast facing bowl at about 6600 ft.
Windy conditions prevented the North Cascades Heli Guides from flying on Wednesday.
Another recent and large cornice failure was observed by the NCH on Thursday in the Cutthroat drainage. Plenty of other unreleased large cornices were noted.
A NC Mountain Guides report for Friday for the Delancey area indicates heavy snow in the near and below treeline and 35-60 cm of storm snow on the Valentine's Day crust. Moderate planar shears were found in recent storm snow layers. New storm slabs were forming and ski tests were producing storm slab and loose dry releases. Whumpfing and cracking was seen above 6600 ft.
There was a skier triggered storm slab avalanche involvement Saturday, resulting in a full burial and beacon recovery. The full details are not known at this time, but the party member is expected to be fine, another fortunate outcome. This avalanche involved a storm slab well below ridgeline at about 6600 feet on a north aspect, in the Cedar Ck drainage, east of Washington Pass.
Central
No recent observations.
South
No recent observations.