Expect a major change in the weather pattern this weekend. Friday should be a wet day, with some new snow at higher elevations. Small wet loose slides may become common with rising temperatures. Avoid steep slopes if you find punchy, wet snow conditions.
A few inches of snow may accumulate at higher elevations into Friday, with rain below that. This could drive some small loose wet avalanches in these areas of new snow, and within areas of unsupportive melting snow. If you see rollerballs and small loose wet avalanches, avoid steep slopes where even a small loose wet slide may push you around. Consider what is above you as well as the slope you are on.
Expect the beginning of the weather pattern change to take hold on Friday. Rain and snow with a slight temperature rise may initiate a round of small loose wet avalanches. At the highest elevations, the new snow may get drifted into thin slabs by the end of the day. A generally stormy weekend is on tap, with avalanche danger on the rise. Dangerous conditions look to develop by Saturday night/Sunday in the mountains with potentially very heavy snowfall and rain.
On Wednesday, an observer near Grace Lakes reported that the snowpack was generally supportive to skis below treeline. Warm spring weather has taken a toll on the snowpack over the past couple weeks. The snowpack is shrinking, and low elevations slopes are melting to bare ground. Be sure to consider all the hazards that come with spring in the mountains. Continue to factor in a good margin for error as hard to predict events like cornice fall, glide avalanches, icefall, rockfall, and a general “shed cycle” in the mountains have been ongoing.
April 3rd, 2019
Spring snowmelt
The snowpack in much of the Cascades has changed dramatically in the past two weeks. The weather has shifted solidly to spring-like patterns. The spring warm-up started in mid-March with a prolonged period of relatively clear skies and warm temperatures. Moving into April, we’re seeing periods of unsettled spring weather bringing rain to many low and mid-elevation slopes and snow to upper elevations.
Very bare southeast aspects of Rock Mtn/Nason Ridge. April 2nd. Photo: Josh Hirshberg
Since the peak height of snow in mid to late February, mountain weather stations in the 4,000-5,000ft range show an average of 27% decrease in height of snow. Looking at weather stations in nearly every zone, the percentage decrease ranged from 22-29%. This year's spring snowmelt is much earlier than normal. 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.
NWAC climatological snow depth data from April 1st. You can view it on our website here.
Spring avalanche considerations
As you head into the mountains there are a few questions to ask yourself common to spring avalanche conditions:
Is there any recent snow accumulation that could cause avalanches? If so, what kind of avalanches could you trigger? And where?
What are the high and low temperatures of the past 24 hours as well as the forecasted temperatures during the time you’ll be in the mountains? Could these create weak, wet snow surfaces?
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?
Glide avalanches and holes opening up in rocky terrain near Mount Herman. Photo: Andrew Kiefer
Other considerations
In addition to daily avalanche hazard, the early snowmelt is creating some 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.
We are approaching the end of our daily avalanche forecasting season. The mountain weather forecast will continue into the spring, and the weather station data is available year round. Keep checking the forecast for conditions updates on the end of season information.
