|Fig 1--GOES W Water Vapor Channel from 500Z, Nov. 2, 2010|
|Fig 2--GOES W Water Vapor Channel from 900Z, Nov. 2, 2010|
|Fig 3--GOES W Water Vapor Channel from 1200Z, Nov. 2, 2010|
"Divergence aloft (and consequently rising motion) is enhanced in the exit region of a cyclonically curved jet streak."
By this point you should be gasping in awe at the wonderousness of this statement. Or maybe not. I'm not going to go into the details of why this is so here, but there is strong support for this statement and patterns associated with other jet streak geometries. (An early description of some other examples of jet streak-lift associations can be found in R. Lee (1955)). But, we can see this statement in action right now for ourselves in figure 3. Among other things, remember that rising motion over the ocean should bring very moist air from near the ocean surface up into the upper troposphere (usually through thunderstorms, but there are other ways...). And here, in the exit region of our cyclonically-curved jet, we do indeed see increases in moisture aloft now as indicated by the green arrow. Move a few hours later, and it becomes even more obvious:
|Fig 4--GOES W Water Vapor Channel from 1600Z, Nov. 2, 2010|
Now we see lots of water vapor being lofted up in the exit region of the jet streak. So, keep this adage in mind when looking at winds aloft and trying to identify areas of rising motion (which is the key to any good forecast). I would note in figure 4 here that while the trough axis is still represented by the red dashed line, our perpendicular halving-line through the jet streak must move with the wind maximum. Based on the "dryest" location, this location seems to have shifted eastward and is now indicated by the yellow line. How jet streaks "move" is yet another fascinating question. For an interesting early paper on jet streak analysis with regards to their motion, try Riehl and Janista (1952). For a very nice description of how temperature gradients determine jet streak location, see Patrick Marsh's blog post here.
I apologize for the technical-ness of this discussion, but...I thought it was cool to see this particular theory played out so obviously on the WV channel. More fun weather observations will come!