Bad News and Good News

What the GFS giveth, the GFS taketh away.

One shouldn't verify a forecast with a forecast, but the Monday-Tuesday storm that I was encouraged about on Saturday and was thinking 5-10" for Alta Collins has really fallen apart in subsequent model runs.  

As an example of how the model trend is not always your friend, here's what the 0600 UTC GFS runs have predicted for snowfall at Alta Collins through 11 PM Tuesday over the past few days.

0600 UTC 2 Dec GFS: 15.5"
0600 UTC 3 Dec GFS: 8.4"
0600 UTC 4 Dec GFS: 6.7"
0600 UTC 5 Dec GFS: 4.3"
0600 UTC 6 Dec GFS: 0.2"

Oh the pain and the misery of it all!  

The reality is that the ensembles never showed this storm to be a lock and I was clearly overconfident. Below is the 0900 UTC 4 Dec initialized SREF showing a range of near zero to 12".  Lots of uncertainty.

Looking at the latest SREF shows a range of about 0-6" through Tuesday night, although most members are now at or below 2".  

Sad and pathetic.  Be grateful for anything we get.  

The good news is that the 2nd storm is still holding together (for what it's worth).  However, there is a wide range of forecast outcomes.  Through 0000 UTC 10 Dec (5 PM MST Friday) the Euro is generating just over an inch of water for upper Little Cottonwood, roughly near the SREF mean based on the forecast above.  The GFS is at the upper-end of the SREF forecast and is going off with 2.3" of water and 34" of snow.  

The GFS is a possible outcome, but an outlier at this long lead time.  With the Euro and most of the SREF members consistent with something in the 8-18 inch range, that's the most likely scenario, with lower probabilities of something bigger than that.  

We'll see how things evolve in the coming days and that Mother Nature takes pity on us.