Avalanche Forecast

A weak low pressure system crossing Oregon on Tuesday should produce light snowfall for the southeast and central east Washington Cascades through early afternoon while little to no precipitation and less cloud cover should be seen closer to the Canadian border.

However, a deeper low pressure system approaching the Oregon Coast later Tuesday should cause shifting and increasing E or NE winds throughout the Cascade range by Tuesday afternoon that will begin to build new wind slabs on unusual westerly aspects especially near and above treeline. Previous wind slab may linger on other slope aspects also in the near and above treeline bands. Watch for firmer wind transported snow on a variety of aspects if you push higher in the terrain Tuesday.

Generally shallow storm slabs should be less sensitive on Tuesday except in areas where they overlie recently buried weak layers below treeline. New storm slabs are most likely in the south and central east Cascades Tuesday. Remember that recently formed surface hoar and surface faceted snow was observed in the below treeline band heading into the last storm cycle. Until more information is received, avoid slopes above terrain traps in the below treeline band where these weak layers may have been buried by the most recent snowfall. 

Continue to identify the 12/17 and less deeply buried PWLs in snowpits and avoid areas where the overlying snowpack is shallower where affecting these layers would be more likely.

Weather and Snowpack

A cold and dry Arctic air mass was over the Northwest last week. The main weather event last week was a day or more of very strong east winds centered on Wednesday that went on a powder wrecking rampage, scouring windward slopes and re-distributing the snow to lee slopes while building sastrugi in other areas. 

Reports indicate the winds eliminated most of the faceted surface snow and surface hoar that formed in the near and above treeline during the cold weather. But these weak surface crystals were still reported below treeline prior to snowfall that fell over the weekend.

A pair of warm fronts moving through the PNW Sunday and again Sunday night allowed some relatively milder Pacific air to finally work it's way east of the crest Sunday evening and night. 3-8 inches of snow fell through Monday morning along the east slopes. 

Recent Observations

On New Years Day reports from multiple snow pits by the the Mission Ridge pro-patrol indicated that basal facets remained intact but were showing signs of rounding and bonding. Mission Ridge experienced a whopper of a snow storm on Jan 2nd when unusual reverse orographic flow produced about 34 inches of new snow along with strong northeast winds. 

A report for Friday 1/6 via the NWAC Observations page for Red Mountain in the central east zone indicated a 10-20 cm deep surface layer of faceted surface snow and surface hoar in the below treeline band. A wind slab also gave a triggered collapse on a ridge top.

The Mission Ridge pro-patrol on Saturday reported that the deep low density heavy snow from early last week had greatly consolidated and stabilized.

The NCMG were out on Delancey Ridge on Saturday and found that snow from a week ago had settled and stabilized. Weak surface layers were noted with surface hoar in the below treeline. Small wind slab was noted in the near and above treeline which was not reactive.

The NCMG were in the Hairpin Valley Monday and observed a natural loose cycle that likely occurred Sunday night. While a couple of storm layers were identified in snowpack tests, the only other direct sign of instability was a small wind slab triggered by cornice fall that again likely occurred Sunday night.