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Friday, January 20, 2012

Trying To Puzzle Out The Mystery Snow

Jerry tries to puzzle out a strange-looking forecast map for northern Indiana:


This is kind of a strange one -- there isn't anything on the surface chart that can explain the forecast for heavy snow in our area. (The area of snow is smack in the middle of a high-pressure system.) The 500mb chart does show a trough, but it's almost imperceptible.









The only thing that I can see that tells me anything is the 700-mb chart, which shows a relatively strong trough, accompanied by a detached slug of high relative humidity. Just looks weird to me.








It almost looks as if the Indiana snow (warm front?) is associated with the Georgia T-storms (cold front?) Like a mid-latitude short wave passing eastwards from the northern Rockies has caught up with a slower-moving southern system, and the two systems are beginning to work in concert. There is a surface low just east of the southern Rockies, in the vicinity of the Oklahoma Panhandle. But it is odd that the system washes out with height.

That surface low may be a warm-core kind of low. It originated on the ITCZ between Hawaii and the mainland more than a week ago and has been drifting northeastwards ever since. As I recall, when that surface low first started off, it was so strong that the NOGAPS forecast suggested it could be near tropical-storm strength. By now, it's highly-modified, but it still exists and it's still affecting the weather.

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