Friday, March 25, 2016

Troughy Uncertainty

Changes are afoot for early next week as a deep upper-level trough and colder air are expected to settle over the interior western U.S.  The 0600 UTC GFS, for example, parks the trough right over northern Utah on Tuesday with a very encouraging pattern for mountain snowfall.

That same GFS run goes big for precipitation, producing about 2 inches of total water equivalent at Alta from roughly noon on Monday through noon on Wednesday.  Wouldn't that be nice.

I'm intrigued, but am keeping my excitement in check.  Much will ultimately depend on the track, position, and intensity of the trough and this is the type of pattern that is typically characterized by considerable uncertainty in precipitation amounts.  Most members of our downscaled NAEFS are generating precipitation during the period, but amounts range from about .75 inches to as much as 3 inches of water.  That's a big range and my impression is that the uncertainty might be even greater than indicated.

Plus, the EC has the trough further west than the GFS, further illustrating the uncertainty in the details of the large-scale flow.

Let's see how this all comes together in the coming days.


  1. Hello Jim,

    The GFS seems to have over-predicted precip over the course of this winter. Because the Euro doesn't have the same local detail (without $$), it's a little harder to compare, but seems to be doing better in terms of trough location, etc.

    By the way, if you are interested, I plotted the wave events at the Kauai buoy against our local storm events. There is a general correlation with some storm events (actually the majority), but not with others: the correlation is strongest with the largest wave spikes. I've only been able to evaluate recent data, so it's not a robust comparison as of yet.

    Best regards, hoping for more snow!

    1. That correlation is really of little value. We have complex numerical weather prediction models for forecasting the weather. These simple correlations are not going to beat them overall.

      The GFS is a socialist model, it gives a little precipitation to everyone.