September 30, 2007

Statistics:

Initial Target: Des Moines, IA
Departure: Westchester, IL 10:00 am
Arrival: Bolingbrook, IL 2:30 am
Intercepts: Storm Lake, IA
Tornadoes: 0
Hail: Non-Severe (0.5 inch estimated)
Wind: Non-Severe (not measured)
Features: Funnel cloud, wall cloud, outflow boundary
Miles: 958

Summary:

Low instability, strongly sheared setup with good directional shear near the surface low made for a decent chance of tornadoes in western Iowa.  Left Westchester late, but made it to the target area in time to catch storms on the northeast corner of the surface low.  Intercepted severe warned cells just south of Storm Lake.  After meeting up with Scott Weberpal and Doug Raflik, witnessed white rope funnel 1/3 of the way to the ground.  Hail and heavy rain from flanking storm prevented decent photo ops.  Continued east through cores to other tornado warned storms witnessing an occluded, horseshoe base before calling off the chase.

Crew and Equipment:

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

Details:

After going for nearly four months without a chase, I was dieing to get out there again.  The weekend looked to be an active one with a setup in the Dakotas on Saturday.  Sunday didn't look as good with the instability, but with ample speed shear and a surface low parked right overhead, the low level shear had enough veering to create a decent chance for tornadoes in western Iowa.
I didn't have great expectations for this chase.  The RUC showed low instability over the target area, and there was a lot of rain and cloud cover lingering around that wasn't helping the situation.  I decided to go for it anyway, noting that there was some clearing to the west and that SPC was sticking to the forecast.  I had to drive Jenny back to her house in Westchester that morning so I didn't get on the road until almost 10, which was rather late for an early afternoon intercept in western Iowa. 

I made pretty good time, however, and the storms were holding off on their initiation until late afternoon.  There is one universal truth and this chase was no exception in demonstrating the fact that Iowans cannot drive.  I guess they are so used to idling through town behind tractors that once they get on the interstate they forget that the speed limit is 70 mph and have never learned common courtesy.  Trucks and cars were blocking the left lane, no one would pass each other.  I cut off a driver who refused to get out of the left lane, who then became irate, driving along side me giving me the finger, flashing his lights, and then, after great effort, finally made it back ahead of me so he could once again block off the left lane so no one could pass.  Nice.

I finally turned off 80 west of Des Moines, kissing the Sunday drivers goodbye, and headed north, just before highway 71.  I had stayed south where the instability was supposed to be better, but the earlier convection and a rather strong inversion had kept anything from firing behind the rain.  Storms were severe and tornado warned on the northwest side of the low near Sioux City, so I headed up in that direction hoping storms would continue to fire to the east around the low.  Near Audubon I caught some building cumulus that was casting picturesque sunbeams.
Not expecting to see much on this chase after the conditions seemed that they would not pan out, I was ecstatic when storms quickly fired overhead.  One rapidly went severe warned and I plotted a course for the intercept.  "Woohoo!"  Heading west toward a newly severe warned cell:
Heading back north coming in from behind on a north-northeast moving storm.
As I approached the storm, it appeared to be organizing with an updraft base. 

I passed a couple of chasers pulled off on the side of 71 so I pulled off to see who it was:  Scott Weberpal and Doug Raflik.

Our storm was on a line that stretched from east to west and wrapped around the northern portion of the surface low.  Looking back west as the storm stretched overhead with clear skies behind it.
With the sun behind us we got some great contrast.  A new updraft tower going up on the back edge of the storm:
We got back on the road to keep up with the storm.  Looking east at a base:
A short while later a lowering condensed and a short inflow tail formed on the front of it.  This was probably a small wall cloud, and you can see what might be a rear flanking downdraft clear slot behind it.

As we approached the base of the storm, we got caught in some rain and hail from the new updrafts that were continuously spawning on the back edge of the line.  We stopped as the hail intensified but still could make out of the base of the storm. 

A white snake-like tube dangled down from the base.  "Is that a funnel?" I thought to myself.  Scott jumped out of his car pointing up excitedly.  I too got out to shoot a picture, but a wall of rain soaked me and I had to retreat for fear of ruining my camera.  The funnel lasted only a few moments and I was unable to get a shot of it.  Here's a shot Scott nabbed through his windshield that I heavily enhanced to bring out the funnel.  You can see it as the white feature in the center of the photo, descending below the cloud base:
I left Scott and Doug and continued north into the core a ways before turning east to intercept newly tornado warned cells on the end of the line.  By the time I had worked myself into a good position on the southern tip of the line, all that left was an occluded base and expanding outflow boundary.  There was still a half hour left on the tornado warning when I intercepted, but they cancelled it early.  I stayed on the base until I was sure it had lined out, however, since I saw a similar looking base drop a tornado on May 5.  I finally broke off at about 7:30 and started my long trek back home, making it in by 2:30 am.
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Conclusion:

This chase was a ton of fun.  I went in with low expectations and I exceeded them, bagging a white funnel cloud.  Sure it didn't touch down, but it was a nice catch after a four month hiatus.  Although I still put 900 miles on the van, this chase was also closer to home than most of my chases this season.  It was also nice meeting Doug Raflik and seeing Scott back on the chase.

 

Lessons Learned:

  • Iowan drivers lack courtesy, and they don't take well to aggressive driving.
  • Don't step out of the car to shoot storm features when its hailing and pouring rain.