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The likelihood of human-triggered and natural wet snow avalanches will increase as the day warms and the sun melts the snow surface. Get an early start and move to gentler terrain or colder slopes as the refrozen crust on the snow surface breaks down.

Last night was the coldest night we've seen in almost a week. Clearing skies helped the snowpack to radiate out some of the energy that it has been collecting during this spring heatwave. The combination of these factors means that there is a thick crust built on the surface of the snow this morning. You will be most likely to run into wet snow problems as the day heats up and direct spring sunshine melts the surface of the snow. Here is a look at the types that you might encounter today:

WET LOOSE AVALANCHES: These types of slides start at a point and fan out as they travel downhill. If you are seeking out corn in very steep terrain before the crust breaks down you may be able trigger wet loose slides that involve just the upper inch or two of soft, wet snow. These slides will be small and manageable for the most part, but could knock you off your feet if you're not paying attention. However, as this crust breaks down these slides will become larger and more destructive as they gouge down into the wet snow underneath. This type of slide can involve most or all of the seasonal snowpack. Take a look at this photo of one such slide that released naturally on Sunday evening at 6:30 PM in the Warm Springs Creek drainage. That slide only had about 500' to pick up steam, you can imagine how large these can become in bigger terrain.

WET SLAB AVALANCHES: Wet slabs occur when water percolates through the snowpack and weakens the bonds at weak layers in the snowpack. We haven't seen much wet slab activity during this warm-up, but our observations have been limited by difficult travel conditions. On Thursday I spotted a large, destructive wet slab that released on an E/SE-facing slope at 9,700' in the Boulder Mtns. Sunday, I went to check in on our weak layers on north-facing slopes and found that even at 8,700' these weak layers were becoming wet thanks to the very warm temperatures. You can read my observation for more details and to see photos of the snowpack I encountered. Predicting the timing of wet slab avalanches is notoriously difficult.

CORNICES: Remember December and early January, when it snowed for days on end? I do, but it feels like a lifetime ago. During that period, large cornices formed in many locations. Warm temperatures are allowing these huge chunks of snow to gradually melt, and they are creeping and sagging downwards as they do. This adds stress to weak spots where the cornice is attached to the ridge and can cause the cornice to break off and tumble down the slope below. When this happens it can entrain large amounts of wet snow (photo) and can even trigger wet slabs on the slopes beneath. As with wet slabs, the timing of cornice failures is unpredictable, but they will be most likely during the heat of the day.

If you head out into the mountains today, pay close attention to how well the snow surface has frozen overnight. Flip your pole around and try to push it through the crust, or hop off your machine and see if you can kick through it with your boots. You can significantly reduce your risk of encountering wet snow problems by starting your day early and moving to colder slopes or gentler terrain when the crust on the surface starts to break down. In many places, we are headed towards what is known as the "spring diurnal" pattern of avalanche danger (danger increases during the day and drops of at night). However, there is something about the amount of water that we just pushed down into the snowpack that makes the hair on the back of my neck stand up a little. Wet snowpacks can behave unpredictably and there is still plenty of water moving down through our snowpack. The likelihood of encountering wet snow avalanches today is lower than yesterday, but I'll feel a lot better about going into big avalanche terrain once our snowpack has had more than just a single overnight freeze.