June 18, 2009

Statistics:

Initial Target: Waterloo, IA
Departure: Naperville, IL 12:15 pm
Arrival: Westchester, IL 4:00 am June 19
Intercepts: Dodgeville, WI
Tornadoes: 0
Hail: Severe (1.00 inches estimated)
Wind: Non-Severe (not measured)
Features: Shelf Cloud, Flash Flood
Miles: 789

Summary:

Warm front setup in Iowa.  Targeted Waterloo and points west where shortwave trough was forecast to initiate storms in the warm sector by evening.  Waited near Alden, IA with other chasers for initiation.  Cap held until after 8 pm when cells started to fire east of Waterloo.  Went after storms but couldn't intercept until over the river in Mississippi.  Caught tornado warned storm near Dodgeville, WI, but storm deteriorated with only shelf cloud noted.  Drove back through Dodgeville catching severe hail and flash flooding and headed east to Madison and than south on 90/94 to home.

Crew and Equipment:

Chase team included Ben Leitschuh.  Equipment:  Kenwood TH-F6A Tribander, Dell Inspiron Laptop.  Kyocera data card and router, Holux 236 GPS, Robotic camera dome with Sony XR-520V.

Details:

After missing one of the most dramatic tornado catches of the year the day before near Aurora, NE, similar conditions presented themselves over Iowa and southern Minnesota the next day.  SPC even went with higher tornado probabilities than the day before.  The forecast was for a shortwave trough to initiate storms in the evening across the warm sector and a stationary front over the Minnesota/Iowa border.
 

Ben Leitschuh and I agreed to team up for this chase.  It looked like the capping inversion would keep a lid on storm initiation throughout the afternoon, so I was able to come into work early and get a full day's work in.  The 4km WRF and the RUC models had storms firing at 8pm.  They differed in locations, however, with the WRF showing initiation along the I-35 corridor and the RUC along the Mississippi.  Ben and I left from my work in Naperville just after noon and headed west on 88 into Iowa.  We would be early if the storms fired at 8, but we hoped the models were wrong and initiation would go much sooner so we had more daylight to work with.

 

A lot of chasers were out on this day and they were all lining up along I-35.  We took highway 20 west out of Waterloo to 35 where we caught up with a large chaser convergence.  We milled around in the parking for hours waiting for storms to fire.  It was miserably hot and muggy too with temperatures in the upper 80's and dewpoints in the upper 70's.  I called out how the evening was going to go down.  We would wait in this parking lot for hours, growing more and more anxious by the minute until 8 pm when storms would finally fire.
8 pm came and went.  Lines of bubbling cumulus had been moving up from the southwest but nothing was breaking the cap.  I did see a boundary on radar pass overhead and should have moved east to follow it.  By a quarter after 8 a few returns started to come in near Waterloo.  The other chasers scoffed at the 20 dbz blips, but it was enough to get Ben and I on the road.  We tore east down 20 back towards Waterloo.  We were way too far west and playing a game of catch up now trying to intercept.  Passing south of Waterloo, we could see the towers, n ow full fledged storms, in the last of the sunlight.
 

We raced after the storms, but were not gaining much ground on them.  Night fell and it became apparent that we would not be able to intercept them in Iowa.  We'd have to cross the Mississippi and intercept in the hilly, wooded terrain of southwest Wisconsin.  The storm went supercellular, exhibited a nice hook echo on radar, and went tornado warned as it crossed the river.  As most supercells do, it also turned right.  This was our chance to intercept as the storm's motion was finally on our side.  We crossed the river and headed north towards Dodgeville.  The storm deteriorated before we got there, but it cycled just as we intercepted north of town and regained a tornado warning.  Ben and I got right into the storm's notch and waited for it to arrive.  We found a spot at the top of a hill with a clearing so we could see the storm come in from the west.  It was actually quite creepy where we were, in the woods, with no lights, smack dab in the middle of a tornado warning.  We could see what looked like a base coming into view as it was illuminated by sporadic lightning.  As it passed overhead though we could tell it was a shelf cloud with a lot of rain behind it.  We got caught in the core and headed south for a core punch to see what was in the storm.

 

In the town of Dodgeville we got into some hail.  Most of it was a quarter inch in size, but some of the stones approached one inch, putting it up to the severe threshold.  The highlight of the night was driving into a flash flood, however.  There was a low spot in the town where run off was flowing across flooding the road with moving water up to a foot deep in places.  We reported the flash flood on Spotter Network and got video of some cars driving through it before we called it a chase.  We headed west to Madison and then south on 90/94, getting home at around 4 am.
 
Conclusion:

It looked for awhile like this chase was going to be a cap bust, but surface based supercells did fire just before dark.  The river prevented us from intercepting the storm at its peak, however, and we caught the deteriorating storm in the bad terrain of southwest Wisconsin.  The day did not live up to its hype as a tornado producer and would have been a total bust if it weren't for the flash flood and severe hail we caught in Dodgeville.

 

Lessons Learned:

  • Southwest Wisconsin is less than ideal for chasing.