Avalanche Forecast

Fair weather should be seen Tuesday with light winds and little change in temperatures.

These conditions should allow for continued gradual decrease in avalanche danger as recent wind and storm slabs further settle and further stabilize. 

Recently formed wind slab should further stabilize on Tuesday.  Wind slabs are most likely on SW-W-NE 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 Tuesday. Head for lower angle slopes if you encounter denser snow over weaker storm snow.

Although we won't list it as avalanche problem watch for wet snow avalanches on steep solar aspects if the sun is out in the afternoon.

Weather and Snowpack

An arctic air mass was over the Northwest with fair, cold weather the 2nd week of January. Surface hoar and near surface faceted crystals formed in wind and sun sheltered areas during this period. Observations over the next few days should help to determine if any of these weak persistent grain types might have survived the atmospheric river event and remain relevant to the forecast moving forward.

An atmospheric river moved over the Northwest about 1/17 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. Three day precipitation totals through about Thursday were about 8 inches at Mt Baker, about 5 inches at Crystal and 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 began a cooling trend. New snow totals through Thursday were fairly light except with about 12-15 inches at Stevens, 9 inches at the top of Alpental with 13 inches 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 the Snoqualmie Pass level.

At Stevens and Snoqualmie Pass the freezing rain crust is about 1 inch (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 Saturday and Sunday deposited about 1-9 inches of new snow with further cooling. Strong S-SE winds Sunday built unstable wind slabs on most lee slopes receptive to transport.

Recent Observations

North

NWAC pro-observer Simon Trautman was back out in the Mt. Herman/Bagley Lakes 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 feet.

A couple reports for the Mt Baker area area available via the NWAC Observations page for Sunday. Skiers triggered 6 inch storm slab on N-NE slopes at about 5500 feet, good bonds were seen to the 1/17 interface at 60 cm. Near Lake Ann wind slab was seen on S slopes and N slopes were scoured. 

Central

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 Dallas Glass and Ian Nicholson 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.

From the NWAC Observations page easy shears and some signs of propagation were seen Sunday at the 1/17 interface near Lanham Lake at Stevens Pass. A skier reported triggering a large storm slab in a chute above Snow Lake on Sunday. A report of snowpack whooping is seen on the Turns All Year page for Smithbrook on Sunday.

NWAC pro-observer Jeff Ward was on Rock Mountain near Stevens Pass on Monday and found good stability and no recent avalanches.

South

The Crystal 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 long distances. Shooting cracks were extending over 100 feet from skis.