Weatherpeople always show smooth contour maps of pressure which convey the impression that winds, which generally blow along isobars, are a smoothly varying field. This photo shows a distinct boundary in the skies above Portland, Oregon last September. Air moves rapidly eastward south of the boundary, and moves hardly at all north of it. High flying jets leave a straight contrail which becomes offset more with time. Of course it is possible that both jets changed altitude and the shear is vertical rather than horizontal.
Copyright © 1999, Kevin T. Kilty, All Rights Reserved

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