Avalanche Forecast

A weak cold front will cross the Northwest on Tuesday. This should bring northwest winds and mostly light snow with a brief, slight rise in the low snow levels.

New small shallow areas of wind and storm slab are possible mainly where the main snowfall is expected in the central Cascades. Wind slab might be found on more south aspects due to northwest winds. Pay extra attention if you see winds transporting snow and find more than a few inches of snowfall.

Previous wind slab layers from strong winds Saturday should further slightly stabilize but could still be triggered on previous lee slopes.

The PWL is getting less likely to trigger in the northeast and central east zones but we will wait for more information before dropping this avalanche problem. Watch for clues to turn around like whumpfing as evidence that the PWL is a problem especially in the near and below treeline zones.

We have varied conditions along the Cascade east slopes. The forecast discussion is the same for the east slopes but the danger rating and problem varies for a potential persistent weak layer (PWL).

An atmospheric river and warm very wet weather was seen last week. This caused more snowfall in the northeast zone, rain in the southeast zone, with a transition in between in the central east zone.

A stormy pattern with cooling was seen late last week and over the weekend with about 1/2-2 feet of snowfall along the east slopes.

A concern is the extent along the east slopes of the PWL from the cold weather at the end of November. On Wednesday NWAC observer Tom Curtis was at Blewett Pass and found sudden collapse test results in faceted snow 15 cm from the ground. On Thursday Tom found similar sudden collapse results due to buried surface hoar at about 50 cm down at 5100 feet on the north side of Mt Cashmere. Tom also experienced whumpfing and heard a natural avalanche.

Further east in the central east zone, the Mission Ridge ski area did not find evidence of a lingering PWL during control on Friday. Tom Curtis and fellow NWAC observer Ian Nicholson visited Jove Peak east of Stevens Pass on Saturday and did not find a PWL up to 5000 feet on south to west aspects.

The PWL is most likely to linger in the northeast and north central zones. The southeast zone should have a much shallower snowpack more affected by recent rain and warm temperatures. However we have no recent observations from the southeast zone.

A report from Delancy Ridge in the northeast zone on Saturday to near treeline indicated storm snow was well bonded to the underlying crust from last week. Small shallow wind slab were forming above 6000 feet but no instability or avalanches were observed. No observations were made above treeline where more widesperad wind slbb conditions were suspected.

A cool day with little if any new snowfall on Monday will have brought some stabilizing.

Terrain anchors have been somewhat buried by recent snowfall but should still add significant anchoring at lower elevations.