Mother Nature is indeed fickle.
|Avenues Foothills, 29 Nov 2010|
|Avenues Foothills, 28 Nov 2011|
|Little Cottonwood Canyon, 24 Dec 2010|
|Little Cottonwood Canyon, 18 Dec 2011|
No doubt about it, December was a miserable month for Utah skiers and it is quite remarkable how different it was from last December. Here's an interesting comparison:
1 Dec Alta-Collins Snow Depth: 25 inches
31 Dec Alta-Collins Snow Depth: 35 inches
1 Dec Alta-Collins Snow Depth: 63 inches
31 Dec Alta-Collins Snow Depth: 116 inches
Based on data at Alta.com, only 15.5 inches of snow fell from 1–22 December this year. For some reason they haven't included additional storms since then, but they were small, so it is safe to say that the monthly snowfall in December 2011 was less than 25". How much fell in December 2010? 131.5" Ah, the good old days.
We've already taken a look at the large-scale circulation from this December, but it's worth doing a comparison with December 2010. To do this, we'll take a look at the 500-mb geopotential height, which is commonly used by meteorologists to examine the upper level flow. Essentially a 500-mb geopotential height analysis is a topographic map of the 500-mb surface. Areas of low heights are associated with upper level troughs and areas of high heights are associated with upper-level ridges, with the flow generally following the height contours.
This December (2011), the mean 500-mb flow featured pronounced split flow over the western United States, with the northern branch of the jet traversing southwest Canada and the southern branch of the jet traversing northern Mexico. It is not uncommon for split flow to occur over the western United States, but the split this December was quite pronounced.
Much was made a few months ago about this being a double dip La Nina. Some suspected that we could have another huge snow year, but as we have discussed, La Nina is only one contributor to the large-scale circulation. Aspects of the large-scale circulation that cannot be predicted on monthly or seasonal time scales can also play a role. Perhaps the La Nina signal will more strongly emerge in the coming months, but for the Wasatch, that signal is fairly weak. We are largely at the mercy of atmospheric processes that, based on today's understanding, are not predictable on monthly to seasonal time scales. In other words, I don't know what is going to happen for the rest of the winter in the Wasatch Range.