Avalanche Forecast
Regions: Cascades - North East.
Expect cooler overnight temperatures and a mix of sun and clouds during the day. In isolated low elevation areas, the chance for wet slab avalanches may still exist. Keep spring considerations in mind, like wet loose avalanches, cornices, and timing your travel to be off slopes before they become wet and weak.
Discussion
Snow and Avalanche Discussion
The snowpack continues to thaw and transition as we enter the spring season. The mild storms over the past couple days brought a total of .35in of rain below 4500ft, and light snow accumulations above. The rain has increased the amount of water making its way through the snowpack on all aspects at lower elevations. A handful of wet slab avalanches have been reported recently throughout the east side of the Cascade Crest. On Monday, a very large wet slab avalanche was observed on a north aspect of Wedge Mountain, a peak near Leavenworth in the adjacent East Central forecast zone. This likely ran on the early February facets. Consider the low elevation, shaded terrain suspect in the East North forecast zone, as many places may harbor a similar structure, especially east and south of Mazama.
In addition to wet slabs, wet loose activity within the recent snow can be expected on steep sunny slopes on Wednesday. Be careful traveling near creeks, as they are starting to open up. Avoid traveling near or below slopes where glides cracks exist, as glide avalanches may occur in isolated locations.
Snowpack Discussion
March 22nd, 2019
Enter Spring
If you’ve been in the snow recently, the wintery conditions of early March may seem worlds away. You may be in for a surprise if it’s been a while since you were in the mountains. The weather has taken a turn towards spring in the last couple weeks and the Cascade snowpack the has undergone major changes. Unseasonably warm temperatures and strong sun followed a month-and-a-half of cold, winter storms. Mid-elevation weather stations stayed above freezing from March 15th-22nd with high temperatures reaching the upper 50’s to low 60’s. For an in-depth survey of the regional snowpack, we’ll divide the terrain up by aspect and elevation.
A graph showing temperatures between 4,000-5,000ft around the Cascades from the 16th-21st.
Aspects
Northerlies
Along with the warm temperatures, the spring sun has played a major role in warming snow surfaces. The result is a snowpack that varies by aspect. In most regions, shaded and northerly slopes remain relatively unchanged. Aside from some settlement and firmer or moist surfaces, the snow on north aspects is almost entirely dry. Even some low elevation north slopes are still holding snow.
Sunny slopes
The snowpack on east through south through west aspects is a different story. The strong March sun melted snow surfaces and drove melt-water into the snowpack. This is most dramatic on steep (over 35 degrees) southeast through southwest slopes below 5,000ft. Â In some areas, you can find meltwater up to 3 feet below the snow surface with drainage channels well established. Between this warm period and rain events in the first half of the winter, the entire snowpack has transformed to melt forms. An important point to note is that as of the 22nd, these solar aspects remain unfrozen and weak. Cooler weather ahead may help strengthen moist to wet layers.
A glide avalanche (D2) released from a rock slab late on the 20th. Lichtenberg Mtn, 5,100ft, SE aspect. Other glide avalanches occurred on the 20th at Snoqualmie Pass and in Tumwater Canyon. Photo: Josh Hirshberg
Elevation
Low elevations
As you travel from low valleys to higher peaks, you’ll notice a major difference in the snowpack based on elevation. With all the low-elevation snow this winter, there are still some cold, shaded slopes holding pockets of snow down to 1,000ft, especially east of the Cascade Crest. However, most slopes below 3,000ft have lost much of their snow cover. Many low elevation, sun-exposed slopes are bare, especially in areas that previously held less than 3 feet of snow. The low elevation snowpack is no longer substantial enough to allow for easy travel over snow or widespread avalanches.
Loose wet avalanches on the south side of Table Mtn, near Mt Baker. 3/17. Photo: Pete Durr
Mid-elevations
At mid-elevations, around 3,000-5,000ft, the snowpack is still deep and layered. Many slopes at this elevation band near and west of the Cascade Crest are holding 6-10 feet of snow. This is also where you’ll find the most dramatic variation in the snowpack based on aspect.
High-elevations
Above 5,000ft you’ll encounter a snowpack similar to what you may have found around the 1st of March. Upper elevations have stayed mostly dry. The most sun-exposed slopes have surface crusts but have not seen much water or change to melt forms below the surface.
Avalanche Problems
Wet Slabs
The recent spring warm-up thawed snow surfaces and allowed meltwater to percolate down through deeper layers in the snowpack. This happened quickly below 5000ft on east, south, and west aspects last week with strong sun. On shaded aspects, the snowpack has largely been quiet, until the recent rain. Here, the snowpack still has very weak facets associated with a crust from early February. With more sun and warming expected on Wednesday, the wet slab problem may continue to run its course in isolated lower elevation areas. Avoid large steep slopes at lower elevations where you find wet unconsolidated snow, and time you travel carefully to be out of consequential terrain before the snow thaws and becomes wet and weak.
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.
Elevations: Below Treeline.
Likelihood: Unlikely
Expected Size: 1 - 2