Avalanche Forecast

The avalanche danger will peak Sunday night through Monday morning during the period of heaviest loading, slightly decreasing later in the day and tapering from north to south across the Cascades. The snow-line through this period will determine the sensitivity and depth of storm and wind slabs. Expect rising avalanche danger with an increase in elevation, and avoid traveling below paths connected to higher start zones. The most significant snowfall is expected at higher elevations and near the Cascade crest, and moderate to strong W-SW winds will easily transport new snow to lee slopes. Locally lower avalanche danger is expected further east from the crest where little to no new snow if expected. 

New storm and wind slab may fail at a few different interfaces; within unstable new storm layers during intense precipitation rates, at the recent snow/new snow interface or down to the previous snow surface comprised of various crusts or weak persistent grain types. These storm slabs may be particularly touchy on the "various crust or weak persistent grain types" interface on the east slopes of the Cascades where this high variability is likely to have been preserved. 

Remember that beneath any new snow received during this storm, a myriad of early season terrain hazards exist, especially at lower elevations. Expect terrain hazards with poorly covered rocks, vegetation and creeks, particularly on south-facing terrain, at lower elevations, and on exposed ridges where wind events have stripped much of the seasons snowcover.

Following 12 long days of high pressure, the first frontal system in quite awhile crossed the Cascades Friday. It wasn't much of a front with only a brief period of light rain and snow. New snow accumulations of 1 to 5 inches were common along the east slopes at higher elevations through Saturday morning. The shallow new snow fell on a variety of surfaces including melt-freeze crusts, surface hoar, and near surface facets. 

Reports indicate that in many areas along the east slopes up to about 6000 feet there was extensive recent surface hoar and near surface faceted growth, due to the strong and consistent temperature inversion. However, the top of the inversion has not been well documented in many east side locations. The distribution of these persistent grain types will be an important distinction as greater loading occurs during the incoming storm cycle.

Warm frontal moisture that arrived on Sunday brought periods of light rain and snow to the east slopes of the Cascades, mainly near the Cascade crest with a sharp decline in precipitation further to the east. Above freezing temperatures were noted at Dirty Face summit and the Lyman Lake Snotel, suggesting light rain pushed up to near 6000 ft in many areas. The warmer temperatures and light rain may have helped wet or potentially destroy recently buried persistent weak layers at lower elevations but more direct information is needed to confirm.   

The underlying snowpack of 1-4 feet along the east slopes is stable with settled old snow from prior to the warm period sitting over the strong Thanksgiving rain crust, buried about 1-2 feet. East-side snowdepths are highest in the Washington Pass area and lowest in the southeast zone.

Observations

North

On Sunday, NCMG found surface hoar buried intact up to 6000' in the Washington Pass area by 10-15 cm of recent snowfall. No signs of recent avalanche activity were noted. 

Central

No recent observations, but see the Stevens Pass zone observations as reports there may be relevant.

South

No recent observations.