Tuesday, November 2, 2010

Thermodynamics of a Utah ridge

This morning's time series from Mt. Baldy, located at the top of Little Cottonwood Canyon, shows that temperatures have climbed for a nearly 24 hour period.  They have climbed at night and during a period when the flow was consistently out of the northwest.  

Further, these increasing temperatures have occurred during a period of weak or perhaps even slightly negative temperature advection at 700 hPa.

The 1200 UTC sounding also shows winds that back marginally with height, consistent with weak cold advection.

So what gives?  In this instance, the warming is related to vertical advection rather than horizontal advection.  Check out the 0000 UTC sounding and you can clearly see the stable layer that was located just above crest level and which is now much lower, yielding the warmer temperatures on Mt. Baldy.

This provides a nice example of how one needs to think of advection as a three-dimensional process.  Further, it is a nice event leading into PCAPS of how large-scale processes can isolate a pocket of stable air in the valley.


  1. The last two mornings have produce wonderful examples of "multiple layer stratification" in that stable air as seen in the haze when viewed from the west looking east. It has been more than obvious that the haze has been isolated into distinct horizontal layers. This afternoon those layers seem to have merged into one hazy pbl.

  2. This is where an aerosol lidar would be nice. PCAPS is coming...

  3. Tyler, the single PBL is sort of true in the afternoon, though an evening hike in the foothills last night revealed some elevated 'clearish' layers within the upper reaches of the cold pool. It seems like the stratification in the lower layers gets blown away by CBL growth, but there still must be some interesting subsiding layers aloft that compensate for components of the upslope flow. What I can never figure out is if the elevated clearer air is indicative of regions of greater or weaker stability...
    This week is a great test case for PCAPS... I'm going to try to work up a nice thermodynamic summary of the event.