Thursday, January 12, 2012


OK, I admit it.  I've been waffling over this large-scale pattern change, at least in terms of what it means for the Wasatch during the coming week.  This is probably clear from recent posts, in which I haven't endorsed the idea of either continued drought or a big storm cycle.  This partly reflects my views on the limits of long-range forecast skill (e.g., Ten-Day Icon-Based Forecasts Are Bogus), but also where northern Utah is relative to forecast storm track early next week.

Here's my thinking.  We are confident that a major pattern shift is underway in the mid and high latitudes.  We are also confident that this will result in a stormy pattern for the Pacific Northwest beginning on Saturday.  The forecast challenge for the Wasatch Mountains is that there is the potential that we remain on the edge of the storminess.  For example, the 1200 UTC GFS forecast brings an upper-level trough and cold front through northern Utah late Sunday Night and Monday, after which a broad, low amplitude ridge redevelops over the west.  Enough moisture spills across the ridge that the GFS this run of the GFS is fairly bullish on precipitation for the Wasatch Mountains for Wednesday and Thursday.

This is what meteorologists call a dirty ridge.  Given the warmth and wind, if we see such precipitation, it would lead to a major avalanche cycle in the Wasatch backcountry where the snowpack is as weak as a house of cards.

On the other hand, if the storm track is just a bit further north, we could get skunked.  Indeed, the GEFS ensemble contains some solutions where this is the case.  Check out the forecasts for next Wednesday morning.

Source: Penn State E-wall
Alex, I'll take solution P005 for $1000 please!  Avoid P003 at all costs.

This is why I'm not "all in" for one forecast scenario and am only "cautiously optimistic," at least for the next week.  

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