Tuesday, October 4, 2011

Not an Easy Forecast

Change is coming, and snow will fall in the mountains, but specifics remain uncertain.

I hate to admit when I don't have a good idea of what will happen, but I don't have a good idea of what will happen!

The 1800 UTC NAM pulls the coveted 0C 700-mb isotherm through the Wasatch by tomorrow afternoon.   Beginning around that time, the snow level should be 8500 feet or lower.  

What makes the forecast thereafter difficult, however, is that the upper-level low is digging and closing off to our south.  Thus, we don't get a nice transition to northwesterly flow and forecasting the where and when of the precipitation bands that pinwheel around the low is difficult.

Bottomline: Keep the skis waxed, the fingers crossed, and stay tuned.


  1. Jim, that four panel forecast image seems to be your go-to. And I can tell something big and moist is headed this way (with winds from the SW) but no more. For example, why does the pressure legend have a 75-450 range? Shouldn't it be around 1000mb? Maybe in between storms you can do an expository post.

  2. Those four panels are basically the "ten essentials" for weather forecasting (although there may be more than ten products included on them). The pressure legend is for the upper-left hand panel, which is an analysis of the pressure and wind on the dynamic tropopause. The dynamic tropopause separates the stratosphere from the troposphere and meteorologists like to track upper-level features on this level. Typical values for the pressure at the dynamic tropopause lie between 75 and 450 mb, which explains the range. Areas of low dynamic tropopause pressure are coincident with upper level ridges, and areas of high dynamic tropopause pressure are coincident with upper-level troughs.

    Yes, this is a techy diagnostic that needs further explanation at some point in the future.