Sunday, November 15, 2015

Here We Go Again

To paraphrase The Who, "meet the new trough, same as the old trough."  Yes, we have another storm rolling in.  Yes, on the large scale, it is remarkably similar to the other storms we've had this month.

The loop below begins yesterday morning and goes through early morning on the 19th when the storm is exiting Utah.  We've seen this movie before.  An amplifying upper-level trough digs off the California coast and continues to strengthen as it moves inland.  Central and southern Utah and Colorado once again appear to be favored by the storm track.

How similar is the large scale in these events?  The loop below shows analyses of the previous two storms and the forecast for the one moving through the west this week.  Identical?  Nope, but quite similar.  

Thus, many characteristics of this storm will be similar to the previous two.  Today we will have the warm before the storm, with warm, windy conditions,  Then a transition to cooler temperatures tonight and early tomorrow morning, then the post-frontal crap shoot.

When it comes to mountain and valley snowfall, however, the devil is in the details.  A small change in the characteristics of the storm can make a big difference given the strong terrain forcing we have around here.  We've already seen some of the weirdness of the past two storms depending on small shifts on the storm track and accompanying precipitation features (how about that 7 inches in 3 hours at Alta-Collins last Tuesday).

Through 5 PM tomorrow, the NAM generates 0.41" of water and 6.7" of snow for Alta-Collins, whereas the GFS is going for 0.49" of water and 8.7" of snow.  Based on the characteristics of this storm, I would be inclined not to jack those up much and to go with something like 4-8" as the most likely range at Alta through 5 PM tomorrow, but would not be surprised if we did better.

Beyond that, you are on your own.  I'm going biking.

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