May 2, 2008

Statistics:

Initial Target: Illinois I-80 corridor
Departure: University Park, IL 2:45 pm
Arrival: Bolingbrook, IL 7:15 pm
Intercepts: Rochelle, IL
Tornadoes: 0
Hail: None
Wind: Non-Severe (not measured)
Features: RFB
Miles: 279

Summary:

Deep surface low with dewpoints into the 60's and pre cold front initiation looked to provide after work chase opportunities in IL.  Headed west on 80 towards weak cells firing in central IL.  Pulled off past La Salle and met up with Kurt Hulst and company before following storm up I-39.  Witnessed horseshoe base on sub severe storm and tracked all the way to Rockford before falling back to I-88 and coming home.

Crew and Equipment:

Solo chase.  Equipment: TH-F6A Tribander, and GPS/Cell Phone equipped laptop.  Photography by Skip Talbot.

Details:

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.
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.
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.

 
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.

 

Lessons Learned:

  • Veering 850 mb winds ruin the moisture for supercell development