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West Slopes Central - Skagit River to South of I-90

Avalanche Watch i

Issued: Mon, January 16, 2017 at 6:09 PM PST
Expires: Tue, January 17, 2017 at 6:00 PM PST

Issued: 6:09 PM PST Monday, January 16, 2017
by Kenny Kramer

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

A drastic change in the recent weather is expected. The timing is uncertain, so watch for changing conditions. Very wet and milder weather should substantially increase the avalanche danger late Tuesday or Tuesday night. Natural wet snow avalanches are increasingly likely later Tuesday.  

Danger Scalei
  • No Rating
  • Low
  • Moderate
  • Considerable
  • High
  • Extreme

Avalanche Problems for Tuesday

Loose Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

  • Avalanche Problemi
  • Aspect/Elevationi
  • Likelihoodi
  • Sizei

Wind Slabi

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.

  • Avalanche Problemi
  • Aspect/Elevationi
  • Likelihoodi
  • Sizei

Snowpack Analysis:

Weather and Snowpack

A pair of warm fronts moved across the Northwest last weekend, with fluctuating temperatures to near or above freezing in areas away from the Passes with milder Pacific air scouring the colder air in the Passes late Sunday night 1/8. This allowed a rain or melt freeze crust to form in some areas below treeline before 5-15 inches of snow accumulated through Monday 1/9.   

A weak low pressure system, tracking across Oregon Tuesday morning through Wednesday afternoon, deposited another 3-6 inches of snow with light winds from Stevens Pass and southward, with Paradise adding another 12 inches. A period of strong E to NE winds occurred Tuesday afternoon through early Wednesday.

An upper ridge over the northeast Pacific Ocean has caused fair weather Thursday through Sunday, with clouds increasing Monday over the Olympics and Cascades with mostly light winds and moderating temperatures west of the crest and at higher elevations. Several NWAC stations warmed into the lower 40's by Monday while strong temperature inversions and breezy cold east winds persisted in the Passes.  

Surface hoar and near surface faceting has been noted widely throughout the range in sun and wind sheltered locations below treeline. Sun crusts have formed on steeper solar aspects over the last few days. Numerous small loose-wet avalanches have been seen Sunday and Monday as temperatures climbed with sunshine. 

Recent Observations

NWAC pro-observers Dallas and Ian Nicholson were in the Crystal backcountry Wednesday to assess the distribution and sensitivity of fresh wind slabs from recent strong E-NE winds. They found that wind slabs were becoming larger as they moved into the near tree line band and exposed ridges. NE-E-SE facing slopes were stripped of recent snow with new reactive wind slabs on N-W-S facing terrain and cross loaded features. In wind sheltered terrain below treeline, the storm snow was right side up and lacked slab structure with excellent skiing conditions.

Some reports are available via the NWAC Observations page for Wednesday and Thursday. in summary skiers triggered wind slab layers on Mt Herman near Mt Baker and in the Slot Couloir on Mt Snoqualmie on Wednesday. Potential wind slab layers were noted at Stevens and at Snoqualmie on Thursday but no avalanches were triggered.

NWAC pro-observer Jeremy Allyn was out in the Alpental Valley on Friday and mainly found that recently formed wind slab in the near and above treeline was settling and strengthening.

Lee Lazarra was taking observations for NWAC in Glacier Creek, NW of Mt. Baker proper on Saturday. Lee found generally good riding conditions in the trees on non-solar aspects. Solar aspects were softening and likely to form sun crusts overnight. Snow surfaces just below and along ridges were variable from last week's winds and Lee found recent wind slabs to be unlikely to trigger in his specific area. Widespread surface hoar growth was noted in the usual spots like creek beds, but surface hoar size diminished higher in the below treeline band. 

Ian was east of Stevens Pass on Monday, MLK Holiday near Lichtenberg Mountain. Any older wind slabs near tree line had stabilized and were not present on SW facing slopes near treeline where they would be expected, if present. The steep solar exposed slopes produced dozens of small, size 1 loose-wet avalanches. 

Detailed Forecast for Tuesday:

Light rain and snow should develop for the North Cascades Monday night while only thickening clouds are expected for the central and south Washington Cascades. Mild freezing levels will continue Monday night with temperature inversions in the Passes and sheltered valleys. Alpine winds out of the SW are forecast to increase Monday night.  

Light to moderate rain, snow or freezing rain is expected Tuesday with increasing SW winds. This weather will begin an increase in the avalanche danger as shallow wind and storm slabs begin to develop. Warming and rain should cause loose-wet avalanches on many steep slopes. 

Possible freezing rain in the passes, especially the Snoqualmie Pass area Tuesday, may build a surface crust and locally limit the avalanche danger.

Avalanche watch issued Tuesday night through Wednesday: A drastic change in the weather pattern to wetter and milder weather should substantially increase the avalanche danger Tuesday night through Wednesday.  

Heavy precipitation with a warming trend late Tuesday and Tuesday night should cause a more widespread natural avalanche cycle.

From Stevens Pass and southward to White Pass, precipitation amounts, type and timing are less certain and High avalanche danger may occur late Tuesday or not until Tuesday night.  

An abundance of weak and cold snow in the upper snowpack combined with the potential for rapid warming and high precipitation rates would lead to very dangerous avalanche conditions during this period and backcountry travel is not recommended later Tuesday.

Observations