Monday, February 27, 2012

Some Thoughts on Tonight's Snow

The forecast models call for a broad upper-level trough to swing into the interior southwest United States today, with the trough axis upstream of Utah by 2300 MST tonight.

I think the forecast for the Wasatch Mountains tonight is difficult for a few reasons.  First, there some subtle but potentially important differences in the track of the upper-level and surface lows in the NAM and GFS models (not shown).  Second, the forecast precipitation ahead of the trough is scattered in nature.  For example, check out the 3-h accumulated precipitation produced by the NAM from 2000–2300 MST tonight.

Note the lack of organization in the precipitation pattern.  If you could run this forecast 100 different times with 100 slightly different initial conditions, you'd probably see quite a bit of variability in where the precipitation falls.  Forecasting with spatial and temporal precision in such a pattern is difficult.

Another interesting aspect of the forecast is the low-level flow direction over northern Utah.  Note that it is from the east, not the west.  Assuming the precip can setup over the central Wasatch, this could be a situation where the Park City resorts fare equal or better than the Cottonwood Canyons.  Often during flow from the east, the snow is heaviest on the Park City side and right along the Wasatch Crest (e.g., Brighton and the Supreme area of Alta).  Solitude, Snowbird, and backcountry further west sometimes don't do as well.

Of course, there's only a brief period of easterly flow tonight.  The flow shifts back to westerly tomorrow morning.

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