Avalanche Forecast

Issued: Mar 26th, 2019 11:00AM

The alpine rating is low, the treeline rating is low, and the below treeline rating is low.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Expect cooler overnight temperatures and a mix of sun and clouds during the day. Variable travel conditions exist. Keep typical spring considerations in mind, like wet snow avalanches, cornices, and timing your travel to be off slopes before warming makes them too wet and weak.

Summary

Discussion

Snow and Avalanche Discussion:

While there are no official avalanche problems in the forecast there are a few potential hazards to keep in mind. Most prominent will be the variable surface conditions that could pose a challenge for some travelers. You may find a range of conditions from soft, new snow, firm frozen surfaces, and punchy, unsupportive wet snow. Creeks are beginning to open up. Tuesday's snowfall didn’t accumulate to enough to create significant avalanche problems, but you may find small isolated pockets of drifted snow at upper elevations. While temperatures have cooled, we’re not completely out of the woods for wet avalanches. Wet slab, loose wet, glide avalanches, and cornice falls all have been a concern in the past week. Continue to monitor the upper snowpack and asses the strength of any wet or frozen layers. Watch for small loose wet avalanches in areas where new snow is now being warmed by the sun.

On shaded aspects, the snowpack only started producing wet avalanches with rain and the warm temperatures in the past week. Here, the snowpack still has very weak facets underneath a crust from early February. The recent occurrence of large wet slabs on wet facets near the ground is concerning, as it tells us water made its way down to these weak layers. Cooling temperatures Tuesday night will help diminish concern for wet slab avalanches but you may still find areas of weak unsupportive snow at low elevations.

Large, dirty, wet slab (D3) debris on Wedge Mountain near Leavenworth. A number of logs were taken with the churning debris flow. Northeast at 3,900ft. 3/25 Photo: Matt Primomo

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.  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.

Valid until: Mar 27th, 2019 11:00AM