Avalog
Register
Get forecast notifications
Create an account to receive email notifications when forecasts are published.
Register
Login
Archived

Avalanche Forecast

Jan 4th, 2019–Jan 5th, 2019
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Snoqualmie Pass.

Avalanche danger will increase as you go up in elevation where more snow accumulated during the recent storms. Expect strong winds to have drifted the new snow into deeper slabs. Stay off of all slopes greater than 35 degrees where you see signs of wind drifted snow. At lower elevations a refreezing snowpack will make travel conditions difficult.

Discussion

Avalanche and Snowpack Discussion

The rain didn’t quite change to snow fast enough for most locations around Snoqualmie Pass. This has left us with a generally wet snowpack this is starting to refreeze. Expect difficult travel conditions, with breakable crust, icy slopes, and full creeks.

A break in the weather Saturday, will allow the avalanche danger to decrease slightly. You are most likely to encounter avalanche hazard at higher elevations where some of the recent precipitation fell as snow.

Snowpack Discussion

January 4, 2019

The first few days of 2019 were active here in the Northwest. A strong weather system impacted the region bringing warm temperatures, heavy precipitation, and strong winds. This weather system did not impact the forecast areas equally. Even within the same forecast zone we can see wide discrepancies in precipitation numbers. The snowpack you encounter this weekend will be largely dependent on where you go and the elevation at which you travel

Storm Precipitation Totals as of Friday Afternoon

Hurricane Ridge: 2.41”

Mt Baker: 6.52”

Stevens Pass: 2.58”

Snoqualmie Pass: 2.27”

Crystal Mountain: 0.52”

Paradise: 2.23”

White Pass: 0.55”

Washington Pass: 1.05”

Mission Ridge: 0.31”

Mt Hood Meadows: 0.51”

A few big stories stand out in the current snowpack: recent avalanche warnings in the northern zones, persistent slabs in the western areas, and a complex and weak snowpack in the eastern zones.

The northern zone experienced the brunt of this latest weather system. This led to two days of avalanche warnings and at least one large natural avalanche cycle. It's tough to say what the snowpack looks like in areas near and above treeline, but we know those areas received substantial new snow.

Photo: Large natural avalanche at Mt Baker Ski Area during the recent storm. -Mt Baker Ski Patrol

Earlier in the week we began forecasting a new persistent slab in our west-slope zones. A layer of buried surface hoar produced avalanches last Saturday, Sunday, and Monday. How did that layer fair after this recent round of weather? In locations like Mt Baker and Paradise, it was well tested with heavy precipitation. In other locations, less water may not have adequately stressed the weak layer. As visibility improves and more observation come-in the picture may become more clear.

Photo: Large remotely triggered persistent slab avalanche in the Crystal backcountry: Jeremy Allyn

In the eastern zones a complicated and weak snowpack exists. Several persistent weaklayers have plagued these regions most of the winter. Don’t expect this to change anytime soon. Snow profiles and snowpack test can give you a glimpse into the persistent layer. Remember, snow profiles cannot prove the absence of a weak layer or that a layer has “healed.”

Photo: Large remotely triggered slide on buried surface hoar from Christmas above Leavenworth on 12/31: Matt Primomo

Avalanche Problems

Wind Slabs

Moderate to strong winds drifted the new snow into firmer and thicker slabs. As you go higher in elevation wind slabs will become larger and easier to trigger. You can use visual clues to identify and avoid wind loaded slopes over 35 degrees. Fresh cornices, blowing snow, snow drifts, and uneven snow surfaces are all signs that wind slabs are in the nearby terrain.

Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 1