Discrete Propagation

It appears that our current cold front moved discretely across Nevada as observed during the 2006 Saints and Sinner storm (see Steenburgh et al. 2009).  In other words, the leading edge of the cold air didn't simply slide across Nevada as a material surface.  A new cold front developed ahead of the decaying Pacific cold front.

Click on the image below for a loop of the RUC2 analysis.  In particular, note how a new trough, cyclonic wind shift, and absolute vorticity maximum develop over northeast Nevada in advance of the trough, cyclonic wind shift, and absolute vorticity maximum over northwest Nevada.  If you doubt the discrete propagation, just watch how the position of the cyclonic wind shift jumps from the -2 C isotherm at 1700 UTC to the +2C isotherm at 2100 UTC.

RUC2 800-mb geopotential height (black contours),
absolute vorticity (red contours), wind (vectors), and
temperature (color fill).  Click to expand and animate.

Cool stuff, and another example of the need to think about processes rather than relying on simple conceptual models of frontal evolution for weather analysis and forecasting.