Avalanche Forecast
Issued: Mar 22nd, 2019 11:56AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet.
NWAC,
Northwest Avalanche Center
Expect thin clouds, slightly cooler air temperatures, and a chance of light rain or snow for Saturday. If the sun comes out, time your travel to be off of slopes before the snow becomes wet and weak. Keep spring-time considerations of wet avalanches and cornices in mind as you move through the mountains.
Summary
Discussion
After a week of very warm temperatures and minimal overnight freeze, sun-exposed slopes have transitioned to mostly melt forms. Shaded, northerly aspects are holding cold, dry snow. Expect clouds, light precipitation, and slightly cooler temperatures for Saturday. In addition to the avalanche problem below, wet slab, glide avalanches, and cornice falls have been considerations this week. There's now less concern for these problems but they're still worth keeping in mind. Don't stand on or under cornices, as they typically fall with warm temperatures.
On the 21st, an observer triggered a large wet loose avalanche on a south aspect of Cashmere Mtn at 8,000ft. A couple of steep rock slabs released glide avalanches in Tumwater canyon since the 20th. Also on the 20th, observers reported glide avalanches from neighboring Stevens and Snoqualmie Pass zones. Significant avalanche cycles occurred in Tumwater canyon with avalanches closing Highway 2 last week. A widespread wet loose cycle was reported near Holden, observed at Blewett Pass, and in Icicle Creek through the 18th. The activity has occurred on basically all but due north aspects, with many at low to mid elevations, and some starting at over 7,000ft.
A natural wet loose avalanche outside of Wenatchee. Old Butte, NE, 1500ft. 3/21. Photo: Mark Peaslee
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.
Problems
Loose Wet
Loose wet activity is occurring less frequently now than five days ago. If the sun comes out, watch for triggering these avalanches on sun-exposed rocky areas, unsupported slopes, and terrain over 35 degrees. Look for signs of instability such as wet, heavy surface snow, rollerballs, and fan-shaped avalanches as clues that you could trigger a loose wet slide. If you experience collapsing in unsupportive wet snow, avoid avalanche terrain. You can check how deep water is traveling through the snowpack by digging and looking for moist layers of snow.
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: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 23rd, 2019 11:56AM
