Avalanche Forecast

Determining how a snowpack will respond to a warm-up like this is tricky. Several days of above freezing temperatures and poor overnight refreezes makes us think we could be reaching the tipping point. We believe the size and scale of wet avalanches are increasing. Even though a cool East wind may help delay the thawing of the snow surface Monday, the sun and warm temperatures will win the battle, and wet snow concerns will abound.

Several large loose wet avalanches were reported from the Baker backcountry Sunday. This increase in size is notable from the other loose avalanche activity this week. Saturday evening we received a report of a large isolated wet slab near Excelsior Ridge on a S aspect at 5400’. Sometimes isolated events such as this are the precursor to more wide spread trends. 

When we’re in spring-like patterns such as this, you can use timing to minimize your risk. Avalanche danger is generally lowest in the morning but can increase rapidly during the day. Travel early, and plan on changing conditions. Remember, slopes you travel in the morning may be very different by mid-day. Be leery of traveling below cornices during these warm periods. They can fail naturally and may act as a trigger for other avalanches.

March 14, 2019

It’s starting to feel a lot like spring. The sun is stronger. Temperatures are warmer. The days are longer. Each year March brings a period of transition for the snowpack. Despite the feel of spring, this transition could take quite a while. Right now, its still winter in the mountains and most of the snowpack is cold and dry.

A northeast through southeast facing bowl in Tunnel Creek, Stevens Pass. The red line shows the transition from northeast to east aspects. Crusts were on the surface of east aspects (right of the line). Surface snow on northeast was soft and dry. March 11th, 2019. Photo: Josh Hirshberg

Aspect dependent snowpacks

A common trend this time of year is the distinct difference between snowpacks on shaded slopes and those on sunny slopes. We might refer to this as aspect dependent snowpacks. The strong March sun can create crusts and send melt-water through the snowpack on sunny slopes.

That process is beginning, right now. As of the 14th, sun-exposed aspects have a crust at the surface. Otherwise, these slopes hold mostly dry layers in the upper 3 feet of snow. The sun now affects more aspects than in the earlier half of the winter. You may find sun affected and melt-freeze crust on any slope that received direct or indirect sunshine. This could include some northwest or even northeast aspects.

Shaded slopes are still holding onto cold winter like snowpacks. That doesn’t mean you won’t find any melt-forms in these areas, but the snowpack looks, feels, and acts more like mid-winter. Avalanche problems can follow a similar trend by aspect. You may see wet avalanche problems on sunny aspects and lingering dry slab problems on shaded slopes.

Two photos taken on March 10th in the Snow Lake area. The left is N facing terrain on Chair Peak with cold, dry surface snow. The right photo shows loose wet avalanches on E facing slopes of Mount Roosevelt. Photo: Ian Nicholson

Balancing problems

So, how do we balance these sometimes opposing snowpacks? In a word, observations. Transitional periods like this require diligence and planning. It seems obvious, but observations you make on a south-facing slope aren’t applicable to N facing terrain. Consider this as you plan your day. Secondly, you’ll want to make observations to verify the avalanche forecast. As we’ve discussed, snowpack structures can diverge during these transitional periods. When your observations line-up with the information you find in the daily avalanche forecast, the forecast is likely valid. If you see observations that don’t match, it’s time to stop, reevaluate, and possibly choose more conservative terrain options.

Making snowpack observations to verify the forecast. Photo: Pete Durr

Less elevated danger and changing trends

You may not find low avalanche danger on every avalanche forecast, but spring is a time of year when less significant hazards can allow backcountry travelers to explore deeper into the mountains. The longer days and often lower avalanche hazard can support stepping into bigger terrain. Remember that low danger doesn’t mean "no danger." Additionally, avalanche conditions can change quickly during spring due to rapid warming over the course of a day or snowfall from potent storms.

We forecast for very large regions. You travel on individual slopes. You may encounter anomalies in the landscape where conditions don’t match the forecast. As with any time you travel in snowy mountains, you can stay safe by using standard travel protocols to minimize your exposure to avalanche terrain and the hazards of the day. Keep your eyes open and be ready to adapt to changing conditions.

What's next?

Winter is far from over. Keep checking the forecast, tracking conditions, making observations, and telling us what you find.