Monday, January 26, 2009

quick and easy

So after cleaning my driveway 3 time in the last 30 hours I'm finally ready to take a break and ski. This last storm total came in at about 36 inches of right side up snow (the opposite of upsidedown). To start a quick disclaimer, I have NOT been in the backcountry for a week and I haven't been keeping up on my avalanche danger forecasts. That being said I am very supprised about Bruce's forcast today of moderate with pockets of considerable. One of the most important things, if not THE most important thing in avalanche forcasting is RATE of loading of the old snow. AGAIN I wasn't following the snowtells but my driveway would tell you that there were times when it was accumulating at upwards of 1 inch per hour, with very high densities. (almost slush, as my snowthrower was not happy about it) I would think that the sensitivity of those old hard slab sitting on facets would have skyrocketed. So I will still be weary of the conditions today, more so than I am told I should. That being said, the reason Bruce came up with the forecast is because of a few things, 1) in the deep snow area's the slab has become very large (over 90 cm) and well consolidated (due to the heat, and long time between snow). The deeper the slab, the stronger it gets. 2) the facets are starting to round out way down there and gain strength. 3)the temperature started warm and slowly cooled. Remember that thin temperature crust at almost all altitudes? Well it could have been very mean, unless you heat it up, then start covering it with snow and slowly cool it so the new snow consolidates well to it. This is exactly what happened. Another thought was those possible areas of surface hoar that could have formed during the inversion. Two things, first, it was pretty warm during that time (less likely to form), and it has been windy, rainy and warm since-- all things that destroy surface hoar. Good news for us. The question will be two fold: 1) will the large slab strenth outweigh the rapid increase in water weight? and 2)will the old large slide paths from earlier this season have a deep enough slab to have the strength to deal with the new rapid loading. (this is the more important question) So I would be trying to stay out o those old paths and especially away from the trigger zones (like rock bands, covered shrubery, anything that brings the heat up from the ground to create a small pocket of facets). Check out Bruces snow pit video at:

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