Avalanche Forecast
Regions: Cascades - West.
A drastic change from the recent weather is underway. Very wet and mild weather should substantially increase the avalanche danger through Wednesday. Natural wet snow avalanches are likely and travel in avalanche terrain is not recommended.
Detailed Forecast
An avalanche warning is in effect through Wednesday afternoon: Expect periods of heavy rain and strong winds to continue Tuesday night through Wednesday afternoon. The wet and milder weather should substantially increase the avalanche danger through Wednesday.
The heavy precipitation with a warming trend through Tuesday night and Wednesday will impact the Washington Cascades. A natural avalanche cycle should occur with the heaviest precipitation.
An abundance of weak and cold snow in the upper snowpack especially near and below treeline 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.Â
Snowpack Discussion
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. Â
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. Â
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.
Warm, wet and windy weather has returned to the Cascades as Tuesday with the rain intensities really increasing Tuesday afternoon, 1/17 to all elevation bands.Â
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.Â
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 1Â loose-wet avalanches.Â
Avalanche Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 1
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 1