This article first appeared on Colorado Firstrax, a site that began in 1995 and was run by David Sauer. The website disappeared rather abruptly without any trace. In June, 2006 a copy of much of the site as of 2001 was uncovered at web.archive.org and the avalanche section was recovered and archived here.
Late March and April are typically characterized by heavier snow and wetter conditions. It almost never rains but you could have a warm spell forming very wet surface snow that freezes each night. This could be followed by more wintery weather and significant storms. The result is heavy spring snow over a crust or lubricated layers. This is the bad aspect about April. The good news is that the weather is warmer and not only is depth hoar no longer forming but firnification has started.
Firnification is the changing of the snowpack from layers of different textures to all one type of snow from the surface to the ground. It is changing to corn snow or firn snow. This is the stuff that looks like the flavored water ice cones at carnivals. When firnification is complete, avalanche conditions are very predictable and you can ski/board things that would have been risky or stupid in mid winter. This firnification usually happens during April and by May is complete but, of course, this can vary with early or late seasonal changes. Be careful in April when the snowpack is in transition between firnification and mid winter layers.
The rest of this article is about typical May conditions when firnification is complete. This is a special time for skiing. This is the time to ski the death chutes with confidence...the couloirs you've been drooling over all winter. This is also the time many skiers hang it up and start gardening or something. Too bad for them because this is the time to ski the truly magnificent runs on the big peaks above treeline.
When corn snow slides it sets up like cement and can be extra deadly. On the other hand it is predictable. When 6 inches of wet surface stuff has melted loose you should be off of the slopes. As long as it freezes every night you have the time in between to be safe. It is key that the snowpack has frozen solid the night before. If you start out in the morning on the previous day's melt and it melts more while your on it you're setting yourself up. Fortunately, the temperatures drop well below freezing above treeline most nights. This is almost a promise in May and very likely in June and even July. If you're sweating in Denver it may be hard to believe.
One thing that can poison a good alpine freeze at night is cloud cover. A warm front moves in and seals in the heat with clouds all night and it may not freeze or may not freeze solid. On the other hand, say it does freeze solid and the next day clouds up early. Now you have rock hard corn snow with no sun to soften the top layer to perfection. The ideal situation is a cold clear night followed by warm sunny day. You start out at sunrise so that you are on top of your run by 11:00 AM. You kick steps on top of frozen corn without postholing. Maybe you'll want crampons and an ice axe if it's steep. Start plenty early and you can hang out, enjoy the view waiting for the sun to soften the snow like a groomed ski area. You take off from the top when it's almost perfect knowing that by the time you get to the bottom it will be warmer there and significantly softer. By three you're at your favorite bar drinking good beer on the deck knowing it's a soggy mess up there by then. If you have an agenda of mountains to ski this spring do the south faces first since they'll go soonest.
Because an early start is essential you might want to camp in the trees under your run or stay with a friend who lives locally. You could even car camp at the trailhead. If you need to drive two hours before you're there and then start hiking you'd better get out of bed at 5 or something. An early start is essential for your own safety. If a large group of people are disorganized and slow in getting moving one of them may end up buried in the afternoon.
Finally, because thunderstorms are now a possibility, getting off the mountain early before convection storms develop is a good idea too. I can't emphasize the need for an early start enough. It matters. If you're the kind of person who can't get out of bed to ski a righteous run than you should stay home and do some gardening or something instead.
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