Avalanche Forecast

545 AM Update Snoqualmie Pass and Central-West Cascade Zones:  Shallow wind and storm slabs may have formed Friday night near and above treeline. In isolated areas the new snow may have buried weak snow, allowing for easier triggering of shallow slabs. Be cautious as you climb in elevation and especially of lee slopes near ridges, looking for signs of recently wind transported snow.    

Previous forecast: Cool with light snow showers at times. Light snow accumulations expected with moderate ridge top winds, mostly from the NW. This should not significantly change the current danger and expect mostly shallow and stable snow conditions. 

If in areas receiving greater new snow, watch for wind transport building shallow wind slabs near ridges.

The recent warm, sunny weather has melted much of the early season snowpack and exposed terrain hazards, especially 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.

545 AM Update Snoqualmie Pass and Central-West Cascade Zones:  4-7 inches of snow fell in the Snoqualmie area with N-NW winds Friday night.  As a result, shallow wind and storm slab have been added to the avalanche forecast with the hazard rating raised to Moderate. The central-west zone has had a convergence zone aimed at it overnight as well...and fresh but shallow slabs likely exist in this zone. 

Previous discussion: Following 12 days of high pressure the first front crossed the Cascades Friday morning. It wasn't much of a front as the high pressure weakened it significantly, with only a brief period of light rain and snow, New snow accumulations of a trace to 2 inches as of Friday afternoon were common along the west slopes.

There was a mix of precipitation types, from light rain to brief freezing rain in the passes to light snow. The main effect of the light rain or freezing rain where it fell, may have been to destroy remaining weak surface hoar or near surface facets that have been developing under the recent high pressure.

The warm and sunny weather over the past 12 days has done a number on the early season snowpack throughout the region, returning many areas to very shallow early season conditions. The most consistent snowpack remains on shaded northerly aspects in the upper below treeline to near treeline where 3-5 feet remain.

The overall snowpack of 2-5 feet along the west slopes is stable with settled old snow sitting over the strong Thanksgiving rain crust, buried about 1.5-2.5 feet.

The high pressure, inversion regime over the past 12 days has created a widely varied array of surface snow conditions, including melt freeze crusts, settled old storm snow, and a mix of recently formed surface hoar or near surface facets (sugary snow) at lower elevations and some shaded terrain. 

Reports vary widely throughout the zones regarding the extent of the recent surface hoar and surface facet distribution. These persistent grain types will be an important distinction when greater loading occurs. 

No human-triggered avalanches have been reported in over a week. Some natural small loose wet slides have occurred on mainly steep sun exposed slopes over the last week, but have become much less frequent over the past several days. Active wind loading has not been observed since late last week.

Observations

North

On Wednesday, NWAC Pro Observer Jeremy Allyn was on Green Mountain and found settled, stable snow conditions. At the summit, northeast slopes were wind affected, but there was no snow available for transport. At peak solar warming, spring-like conditions were found on steep solar aspects. There was little to no snow below 5000 feet. 

On Wednesday, the Mt. Baker professional patrol reported no glide or other avalanches. Surface snow softened in the sun. Snow on non-solar is staying cold and drier, but without near surface facets or surface hoar, likely due to being above the inversion.

Central

On Wednesday, NWAC Pro Observer Jeff Ward was on Jove Peak where he found little to no avalanche concerns. He found a mix of conditions, ranging from corn-snow on solar slopes, to powder on lower angle slopes at lower elevation, and large (1 cm+) surface hoar in the valleys. With the variable snow surfaces, he suggests it is going to be difficult to predict how the next storm snow is going to bond to these surfaces.

Also Wednesday, see a nice observation from the Stevens Pass area posted to the NWAC observations page:

Surface hoar over a breakable melt freeze crust, image Matt Hartman.

Professional Observer Dallas Glass skied non-solar slopes in the Alpental valley on Monday. He observed a very strong temperature inversion up to 4800' with cold, dry snow below the inversion. He found moderate easterly winds near treeline at 5200’. No snow was being transported. He found no avalanche problems that affected his travel. He noted the biggest travel hazard was low snow cover. Surface snow conditions were extremely variable.

South

Professional observer Ian Nicholson was in the Crystal backcountry on Wednesday. He found an overall consolidated, stable snowpack. He found limited good skiing on NE-facing slopes on a surface layer of settled powder, near-surface facets, and surface hoar. He noted an impressive volume of snow lost during this high pressure ridge. He noted that the easterly wind was picking up over the course of the day, but was not transporting snow.

A DOT crew was at Chinook Pass on Tuesday and reported noteworthy surface hoar up to 1 cm below the 4500' inversion.