This animation shows the circulation patterns over North America at altitudes of about 5.5km.  The time period is November 30 - December 26 1996.  The map actually displays the 500mb "constant pressure surface" and you can see three or four "Rossby Wave" troughs (and ridges) developing and passing across the continent over this three week period. These cold waves will be dragging surface cyclones and fronts with them. The winds at this altitude will be geostrophic and therefore parallel to the contours.

To re-play the animation hit "reload".

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