Water vapor imagery, and loops, show a very complex structure within the cutoff low west of California this afternoon. The 2300 UTC water vapor image (above, upper-half of troposphere depicted) indicates three vorticity maxima within the sysytem, oriented nearly north to south - positions of these indicated by red arrows. There are also a strange series of sawteeth in the image along the north edge of higher WV that is positioned south of the upper-level jetstream. These appear to be elongating S-N and translating rapidly northeastward (they are located between the two black arrows). What are they? - I have no idea. Comments or suggestions?
Brad Muller comments from Florida - Hi Bob, I tried to post this comment to your blog three times before I gave up…I used my name, but it ate the comment without posting it anyway…hope this gets to you.
Those sawtooth signatures are "transverse bands" or "transverse waves." They occur with jet streaks when there is strong vertical wind shear. I talk about them in my Satellite and Radar Weather Interpretation course:
http://wx.db.erau.edu/faculty/mullerb/Wx365/Transverse_waves/transverse_bands.html
They also are often seen on the poleward edges of the anticyclonic outflow jets that occur from the tops of hurricanes (scroll to bottom):
http://wx.db.erau.edu/faculty/mullerb/Wx365/Hurricanes/hurricanes.html
Both the 500 mb (above) and 300 mb (below) NAM 12-hour forecasts valid at 0000 UTC this evening indicate a complex structure, albeit one that is more west-east oriented than what's actually present. This has been a difficult system for the models, with predictability seeming to decrease as the event has evolved (see earlier post). Exactly how things will play out for the Southwest and northern Mexico remains somewhat uncertain, and it will be an interesting weekend.
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