Friday, December 1, 2017

Pray for Snow

I woke up this morning and promptly tweaked my back.  While not good for me, it could be good for you.  This may be non-scientific, but since I won't be able to ski for a few days, the likelihood of snow increases dramatically.  The effect is similar to when I leave town. 

Thus, it is no surprise to see a relatively optimistic forecast by this morning's NAM, which calls for a cold-frontal passage late Sunday, followed by a band of frontal precipitation. 

Perhaps more intriguing is the cold, northwesterly flow that follows Sunday night, with orographic precipitation over the Wasatch and an environment that might even spark some lake effect.

At the Alta grid point, this NAM run produces 0.28" of water and 6" of snow. 

That's not a lot, but if we were to get into an unstable post-frontal flow, the NAM often underdoes the precipitation in the Cottonwoods, especially if the lake effect gets going.   

On the other hand, given the model flip-flops of the past few days and the amount of spread still in many ensembles, we should examine what the ensembles are doing.  The downscaled SREF still has a pretty wide spread for this event at Alta. 

The ECMWF ensemble is a bit wetter, with a mean at Salt Lake City (I don't have access to forecasts for Alta) of about 0.55" of water, but a range from about .2" to 1.0".

My view of this is that there is some hope for Sunday's storm, but much will ultimately depend on details of the post-frontal crap shoot that are not predictable at this time.  Expect a bumpy forecast ride through the weekend due to model jumpiness and hope that Mother Nature comes through. 

One positive is this will be a cold event, with precipitation falling as snow at the resorts.   Hooray for that. 

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