Avalanche Forecast
Regions: Snoqualmie Pass.
The avalanche danger should greatly increase west of the crest starting Friday afternoon.
Detailed Forecast
West flow and an atmospheric river (aka the Pineapple Express) of warm front moisture will begin moving over the upper ridge and to the Northwest on Friday. Rain or snow should become moderate to heavy mainly in the Olympics and north to central Cascades by Friday afternoon and continue Friday night with rising snow levels. Weak offshore surface flow and light cooler east winds may do little to delay a change to rain in the lower Cascade passes Friday afternoon and evening.
In all areas west of the crest loose wet and and wet slab avalanches will be listed at the avalanche problems on Friday. West of the crest these problems should be more likely in areas with the most recent snowfall and expected greater rainfall on Friday which is the Northwest, Central West and Stevens Pass zones. But loose wet or wet slab avalanches should be seen in all areas west of the crest.
Often loose wet avalanches occur just prior to wet slab avalanches. Avoid steep slopes if you are in increasing heavy rain and start to see wet snow deeper than a few inches or increasing natural pinwheels or rollerballs. The avalanche danger should continue to increase Friday night.
There is some uncertainty in this forecast. If the heaviest rain occurs Friday night then the greater avalanche danger may also occur Friday night.
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Snowpack Discussion
Snow on the back end of the last storm west of the crest Sunday and Monday was mostly in the 8-25 inch range except at Stevens Pass where the extra snow from Saturday night caused a storm total of about 33 inches. No significant avalanche activity was reported west of the crest by professionals Monday or Tuesday except at Stevens Pass. Both Monday and Tuesday mornings the patrol at Stevens triggered 15-20 inch storm slabs on N-NE aspects of Cowboy Ridge.
Here is a video from Monday by NWAC pro-observer Dallas Glass at Stevens Pass via our YouTube Channel. It should give an idea of the snow available for avalanches on Friday.
Our NWAC pro-observers were at Stevens for a class on Tuesday and found a potential persistent weak layer of 2 mm facets on the 15 January crust. Here is a link to the Instagram video. While in this particular pit it gave a pretty remarkable score of PST 15/100 End it will not be listed as an avalanche problem due to a lack of activity on this layer, inconsistent distribution and that is should require a very large trigger.
In most areas west of the crest the middle and lower snowpack should consist mostly of stable rounded grain or melt forms and crusts from warm periods this winter.
A weak dissipating front is moving across the Olympics and Cascades on Thursday. Snow and rain amounts are expected to be light and not have a great effect on snow conditions.
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, Treeline.
Likelihood: Possible
Expected Size: 1 - 1