Saturday, December 8, 2012

Cottonwoods Magic Kicks In

When you are a meteorologist, there are bound to be some days when you take your lumps.  Today is one of those days.  All clues pointed to a fairly weak storm today, but the magic of the Cottonwoods kicked in and we're now beyond the 2-4" I expected.  However, I'm not going to complain and neither should you.

The 1502–2112 UTC (0802–1412 MST) radar loop below shows the highly localized nature of the snow, which has been confined primarily to the Salt Lake Valley and Wasatch Mountains to the east.  

Lake effect?  Except perhaps near the end of the loop above, I don't think the lake has played much of a role so far.  The flow at the top of the Snowbird tram has been westerly, which isn't favorable for carrying lake-effect precipitation into the Cottonwoods.

In addition, usually lake-effect precipitation is characterized by cellular radar echoes and convection.  I didn't see much around the Salt Lake Valley for much of the morning and early afternoon to indicate there was any lake-effect convection.  Perhaps the lake will eventually kick in, but thusfar, I don't think it's played a significant role.

Instead, there was local precipitation enhancement within a cloud band that extended from southeast Oregon, across northwest northeast Nevada, and then eastward across northern Utah.

Source: NCAR/RAL
Incredibly, the area around and upstream of the Cottonwoods was the only place it was snowing along that cloud band.

Why?  I have ideas, but none of them are very compelling or easy to explain in a few sentences.  Maybe you have better ones.  I'm just going to say it was the Cottonwoods magic and not spoil a good thing.

The new snow has piqued my interest, but I'm currently laid up with a bad back and unable to ski.  Transporting my son from Snowbird this afternoon was serious torture.  The only turns I got involved following the red snake back down the canyon!

Get some for me tomorrow.  


  1. Do you think that the lake plays a role in allowing the northwest flow to accelerate at low levels? Then when it runs into the valley, friction and surrounding terrain that does not let the flow turn forces lift? In this way, the lake could play a role by just being fairly flat (low relative friction) and upstream of a perfect terrain setup.

    1. Adam:

      Maybe, but one thing we learned recently is that the topographic funneling of northwesterly flow into the Salt Lake Valley can be a powerful mechanism for precipitation enhancement. That could be playing a role today, along with the overlying band in the westerly flow at and above crest level. See for discussion of the funneling effect.

      One thing is for sure, the storm morphology has been shifting in the past hour, so this discussion is most relevant for the processes prior to about 2 PM.