Avalanche Forecast

Mostly cloudy early Monday with a chance of a few light snow showers, light winds with cool temperatures. Clouds should decrease becoming partly cloudy late Monday.

These conditions should allow for a gradual decrease in avalanche danger as recent wind and storm slabs begin to settle and stabilize. 

Allow existing storm and recent wind slabs time to continue stabilizing on Monday. Wind slabs are most likely on NE-W-SW aspects in the passes and Crystal area due to recent strong E-SE transport winds. In the Mt Baker area, look for wind slabs on a wide range of aspects due to shifting winds. Watch for recent wind effects near and below ridgelines and avoid steep slopes with obvious signs of recent wind loading.  Wind slabs will likely extend into the upper portion of the below treeline band in the Crystal Mountain, Snoqualmie and Stevens Pass areas.

Storm slabs should become more stubborn to trigger Monday. Watch for denser snow overlying weaker storm snow and stick to lower angled slopes. 

Weather and Snowpack

An arctic air mass was over the Northwest with fair, cold weather last week. Surface hoar and near surface faceted crystals formed in wind and sun sheltered areas during this period. Recent observations on Thursday and Friday helped confirm that we aren't dealing with any older layers formed during this period.  

An atmospheric river moved over the Northwest Tuesday and Wednesday with highly variable weather seen throughout the Cascades during this event. Heavy rain was seen up to about 5000 feet in the north Cascades and up to about 6000-6500 feet in the south with snow at higher elevations. 3 day precipitation totals through noon Thursday were about 5 inches at Crystal and 8 inches at Mt. Baker with 1-2 inches at the Passes. Sleet and freezing rain Tuesday at the Passes changed to snow at higher elevations at Stevens and Snoqualmie on Wednesday. An avalanche cycle likely occurred in areas west of the Passes during this period. 

With the arctic air mass finally displaced and easterly flow abating in the Passes on Thursday, Stevens and Snoqualmie Passes warmed to near or above freezing while areas further west like Crystal and Mt. Baker saw a slow cooling trend. New snow totals through Thursday were fairly light except with about 12-15" at Stevens, 9" at the top of Alpental with 13" at the base. Below the new snow a freezing rain crust has been reported in the Stevens Pass area and the upper half of Alpental with varying reports of a crust at Pass level.

At Stevens and Snoqualmie Pass the freezing rain crust in about 1" (2-3 cm) thick and generally ski supportable. Mt. Baker was the benefactor of steady showers Thursday afternoon and night, picking up about 2 feet of new snow through Friday morning.  E-SE winds were strongest in the Crystal area Friday, with light to moderate E-SE winds observed or reported elsewhere.

Showers late Saturday and another band Sunday, deposited about 4-8 inches of new snow as of Sunday afternoon. Very strong S-SE winds Sunday quickly built unstable wind slabs on most lee slopes receptive to transport.

Recent Observations

North

The Mt Baker pro-patrol and NWAC pro-observer Simon Trautman reported several large wet slab and glide avalanches from the Mt Baker area on Wednesday following the period of heavy rain. Simon was back out in the Mt. Herman/Bagley L. area Friday. A density change about 10" (25 cm) down in the new storm snow was reactive on small test slopes and the depth of widespread natural storm slab avalanches that had occurred Thursday night. At least one unintentional skier triggered storm slab was reported on this layer in the Mt. Baker backcountry Friday. Recent wind loading was apparent on many aspects near and above 5000'. Weak wet snow below the recent storm snow could still be found below 4000 ft.     

Central

Reports Wednesday in the Stevens Pass area indicated poor bonding to the freezing rain crust. NWAC observer Dallas Glass was out in the Stevens Pass area Wednesday and reported sensitive 25-35 cm of wind slab on westerly aspects above the 1/17 freezing rain crust in the near and below treeline bands. On Friday, Dallas reported storm slabs failing on a preserved storm interface just above the freezing rain crust in snowpack tests and on short test slopes. Wind slabs were sensitive at the same interface and most likely to be found on westerly aspects near and below treeline in the Stevens area.

NWAC observer Ian Nicholson was out in the Alpental Valley on Friday and found storm slabs 20-25 cm thick and poorly bonded to the 1/17 freezing rain crust. Wind slab distribution near treeline proved variable and touchy in pockets. Both avalanche problems required conservative terrain choices.

On Sunday, NWAC observers were back in the Stevens and Snoqualmie Pass areas. Strong south to east winds was actively transporting recent storm snow and building wind slabs on all but windward slopes. Many windward slopes, NE-S facing, were scoured to the 1/17 crust. Storm slabs were gaining some strength but remained touchy in some areas below treeline. In both areas, recent storm snow was highly variable due to wind effects, but in sheltered areas averaged 12-16 inches.     

South

Crystal Mtn Pro patrol reported extremely sensitive new wind slabs on NW aspects Sunday morning. About 4-6 inches of new storm snow were transported by very strong S-SE winds overnight and early Sunday morning. This built very sensitive wind slabs on lee slopes by early Sunday. Wind slabs, mostly in the 6-8" range, released sympathetically and were running far distances. Shooting cracks were extending over 100 ft from skis.