Tuesday, December 20, 2011

Diverging Forecasts

We have an interesting forecast scenario for tomorrow night - one that will test the nerves of most meteorologists.

A few days ago, the computer models were keeping storms to our north this week, but suddenly, on Sunday, they decided to drop an upper-level trough into Utah late tomorrow (Wednesday) and tomorrow night.

The two major computer models run by the National Centers for Environmental Prediction for the National Weather Service are still bringing that upper-level trough into Utah, but with drastically different predictions for how much snow will fall.  The NAM model  pushes the trough axis across the Wasatch Range by 11 PM tomorrow night, but with only light, scattered precipitation.

On the otherhand, the GFS model has similar timing, but a much deeper, wetter trough that would give us a period of snow in the Wasatch Mountains.

The one thing that is "clear" from these forecasts is that we can count on much of the gunk from our ongoing inversion episode to be scoured out.  What is less clear is how much snow the Wasatch will get.

My rule of thumb is to lean to the GFS in situations like this as it seems to better handle the evolution of large-scale weather systems like the upper-level trough.  That being said, even the GFS model isn't calling for a huge snowstorm in the Wasatch Mountains.  Perhaps a few inches if we are lucky as we simply lack a prolonged period of moist cross-barrier flow to give us a big snowstorm.

The bottom line is we need to hope Mother Nature is more generous than these computer model forecasts!  Anything we get now will help as we head into the holiday week.


  1. The latest (18Z) GFS run is hinting at a large-scale pattern shift early next week. This is the first run that looks promising. Even if it is the 5-7 day outlook, you have to take any hope you can at this point and keep your fingers crossed.

  2. Oooh...you are right. Let's see if it holds for a few model cycles and if we start to see some consistency in the ensembles and with the ECMWF.

  3. Lets keep the fingers crossed...mine are. I never saw huge pressures like what they had in the "omega" high pressures of earlier dry periods. REUNITE THE SPIT!!!!