Stevens Pass

Springtime is all about timing. Early starts and finishes allow one to be off of slopes before the snow becomes wet and weak. Keep wet avalanches and cornices in mind as you move through the mountains. 

On Saturday, an observer found one of the better refreezes of the snow surface of the past week. Last week, an extended period of very warm temperatures and minimal overnight freezes initiated a prolonged wet loose avalanche cycle. At this point, most sun-exposed slopes have made the transition from a winter like dry snowpack to a spring-like snowpack of melt forms. Shaded, northerly aspects are still holding cool, dry snow, with variable conditions. In addition to the avalanche problem below, keep normal springtime precautions in mind. Creeks are beginning to open up, wet slabs and glide avalanches may still occur, and cornices may break off from ridgelines. 

On the 21st, NWAC Avalanche Specialist Josh Hirshberg observed a fresh glide avalanche (D2) that released from a rock slab on Lichtenberg Mtn, SE, 5100ft. On the 19th on an adjacent slope, an observer reported a natural wet slab big enough to injure, bury, or kill a person (D2). Another large (D2) wet slab occurred in Tunnel Creek, S, 5,200ft late on the 17th. Observers reported similar avalanches at Snoqualmie Pass, Crystal Mtn, near Mt Baker, and Mt. St. Helens. Since the 13th there's been widespread natural wet loose avalanches with a peak of activity on the 17th. Locally these have occurred on the southeast face of Lichtenberg Mtn, West aspect of Snowgrass Mtn up to 7,200ft, and southwest aspects near the Skyline and Windy Mtn areas. Some of these avalanches were big enough to bury or kill a person.

A glide avalanche (D2) released from a rock slab late on the 20th. Lichtenberg Mtn, 5,100ft, SE aspect. More snow had yet to release from this starting zone.

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.  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.