Avalanche Forecast

Snow and Avalanche Discussion

Expect warmer temperatures on Friday and some sun. The recent storms left a sharp gradient of snowfall accumulation between Mt. Baker and Washington Pass, where about 9" of snow accumulated, but only a trace at Washington Pass. If you find more than about 5" of new snow, expect the avalanche danger to rise quickly with daytime warming. Strong April sun and even warmer temperatures than Thursday may initiate a round of small wet loose avalanches. These may occur within new snow but can gouge into deeper layers. Be especially heads up around steep sun-exposed slopes. Rollerballs and pinwheels are good signs that loose wet avalanches may follow. Even small loose wet avalanches can have severe consequences if they carry you into terrain traps like gullies or over cliffs. Use caution near slopes 40 degrees and steeper if the snow surface becomes wet and sticky. As you travel through the terrain, factor in a good margin for error as hard to predict events like cornice fall, glide avalanches, icefall, rockfall may occur sporadically. The more complex the terrain, the more likely it is you will see, or hear the mountains shedding their winter coat. 

WSDOT crews hard at work clearing Highway 20 of wet avalanche debris. April, 2018. Matt Primomo photo.

April 9th, 2019

Spring Conditions

The snowpack and weather have shifted solidly to spring-like conditions. A major warm-up started in mid-March with a prolonged period of strong sun and warm temperatures. This created a major difference between the snowpack on sunny slopes and that on shaded aspects. More recently, warm, wet, and sometimes weak spring storms have brought more rain than snow. The bulk of the precipitation with these storms focused on the southern forecast zones. Even so, mid-elevation rain established a dramatic snow line (about 4-4,500ft) below which the snowpack is minimal to non-existent in most zones. Going into the second week in April, intense snow and wind drove a prolonged period of High danger at Mt Hood.

A crown of a very large avalanche (D3+) above Mt. Hood Meadows resort. 04/08/2019. Photo Credit: Peter Moore.

Challenging Weather Forecasts

The Cascades have been experiencing unsettled spring weather with rain to many low and mid-elevation slopes and snow at upper elevations. Spring weather forecasts in the Cascades are notoriously challenging. With these storms, the weather models have been inconsistent and the accuracy has been limited to 12-24 hours, at best. A trend has been significant precipitation amounts for the Mount Hood area and other south-central Cascade volcanoes. 

Very bare southeast aspects of Rock Mtn/Nason Ridge. April 2nd. Photo: Josh Hirshberg

Shrinking Snowpack

From the peak height of snow in mid to late February through early April, mountain weather stations in the 4,000-5,000ft range showed an average of 27% decrease in height of snow. The percentage decrease ranged from 22-29%. This year's spring snowmelt is much earlier than normal. If you’re traveling in the mountains, the loss of snow coverage is most noticeable on southerly, sun-exposed slopes and below 4,000ft. On northerly aspects and slopes above 5,500ft, the snowpack has seen less dramatic changes and has even maintained some dry layers. On upper elevation shaded slopes there’s still potential for large wet slab avalanches with prolonged warm temperatures or high elevation rain events.

A natural loose wet avalanche (D1), Lichtenberg Mtn, N, 4,850ft. 4/7/2019. Photo: Will Govus

Spring avalanche considerations

As you head into the mountains there are a few questions to ask yourself common to spring avalanche conditions:

1. Can you trigger avalanches due to new snow?

   1. If so, would they be storm slabs or wind slabs? And where?

2. Can you trigger avalanches due to warming or rain?

   1. Will recent snow be warmed enough to result in loose wet avalanches?

   2. Will these avalanches be predictable point releases or more destructive wet slabs or gouging loose wet avalanches?

   3. What are the recent high and low temperatures and the forecasted temperatures during the time you’ll be in the mountains?

   4. How is the cloud cover contributing to the melting or freezing of surface snow? Did clear skies allow for a sufficient overnight freeze? Will the sun be strong enough to weaken surface layers?

Debris from a natural loose wet avalanche (D2), Lichtenberg Mtn, SW, 5,000ft. 4/7/2019. Photo: Josh Hirshberg

Other Considerations

In addition to daily avalanche hazard, the early snowmelt has created other travel considerations. Some roads and lower elevation slopes may not have enough continuous snow coverage for travel on snow machines. Holes melted around rocks, trees, and creeks could create a fall hazard. When nighttime temperatures and cloud cover allow for surface freezes, bring appropriate equipment to mitigate slip and fall hazard on steep slopes.

The last daily avalanche forecast for all zones will be issued for April 14th. Statewide mountain weather forecast and weekly avalanche condition advisories will continue through May. The weather station data is available year round. Keep checking the advisories and help us out by submitting observations when you are in the mountains.

Glide avalanches and holes opening up in rocky terrain on an east aspect of Mount Herman. 4/3/19 Photo: Andrew Kiefer