A deep surface low was forecast to move up through Iowa
along the MS river valley, bringing good directional shear and trailing cold
front. Storms appeared likely in western IL, but there was some
question about how good the moisture would be. |
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I got in the path of one of the storms just west
of La Salle, IL and pulled off I-80. By coincidence Kurt Hulst and two
other chasers riding with him were parked across the street, calling me on
the ham radio. We chatted for a bit and then caravanned up I-39 to
keep up with what wasn't more than a shower. |
Near Rochelle the storm had what appeared to be a horseshoe
shaped rain free base. This sub severe cell that could barely be
called a storm was the best base I had seen yet this year. It was a
real slow start to the season. |
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Dewpoints were dropping into the 50's. It appeared
that southwest 850 mb winds were mixing out moisture at the surface.
The low topped convection wouldn't have enough moisture to organize into
supercells. Kurt and company decided to head back east on 88 and I decided
to pursue the line of storms north on 39, hoping that the backing winds near
Wisconsin would provide better low level shear and less moisture mixing.
The cells never got their act together, however and I eventually dropped
back to 88 myself, noting a rainbow on the back end of the line. |
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Conclusion: Today was a big bust, but
my expectations weren't that high anyway for the cold front play. The
watch and warnings sure got my hopes at the start of the chase, however.
Even if I had been able to leave work earlier (or not work), I doubt I would
have seen much more with the Iowa tornado warnings. The cells never
looked very organized and were always embedded. |
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Lessons Learned:
- Veering 850 mb winds ruin the moisture for supercell development
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