Sunday, October 27, 2019

GFS 1, NAM 0

It's a beautiful Octobruary day in the Avenues and on the University of Utah campus where light snow is falling and creating a beautiful scene with the fall colors.  My little corner of northwest campus is especially nice where the University has gardened with drought-resistant plants.  So much nicer than grass!

This morning, I took a look back at the forecasts produced by the models initialized at 0000 UTC 27 October (1800 MDT Saturday).  The contrast between the GFS and the NAM is significant.

Below are 24-hour accumulations (water equivalent) generated through 0000 UTC 27 October (1800 MDT this afternoon).  The GFS (top) has about .1-.25 inches falling over the Salt Lake Valley, with higher amounts in the central Wasatch.  The NAM (bottom) has nothing.   

Downscaling and applying a snow-to-liquid ratio to these forecasts and you get accumulations of 0.5 to 2 inches on the benches and greater than 4 inches over the central Wasatch from the GFS.  Nothing from the NAM (naturally). 

If you are wondering, automated sensors at Alta-Collins suggest 3-4 inches of snow as of 10 am.  Accumulation in my neighborhood is surface dependent, but I'm willing to call it measurable and thus give the GFS a 1-0 win over the NAM. 

So, in this instance, yesterday afternoon's guidance from the GFS was superior.  However, that's a sample size of one.  We'll see how it does in the coming weeks.

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