04/24/09 Iowa Breaks the CAP

Parkersburg, IA the site of last years E-F5 tornado Friday evening

Friday, was a great day to storm chase. In fact, it was one of my favorites in quite sometime that didn't manage to be a "tornado day". Almost every storm was picturesque and slow-moving leading to many opportunities to sit back and enjoy some nice convection. Despite the high-bases (LCL's) that limited any chance of tornadoes it was a pleasing day for myself. My target area of Fort Dodge, IA was a great area to chase. I'll remember this for future chases too. The SPC forecasted my target area in a SLGT risk. Most chasers instead of chasing this setup drove to Oklahoma and Kansas to get a head start for the MDT risk the next day. I would have headed there too, but my chasecation doesn't start for a few weeks so I decided to make the best of it and take what I could get. Bright blue skies all morning in north central Iowa lead to CAPE near 3,000J/kg by late-afternoon. A cold front was just northwest of my target area and was very slowly progressing south through the day. The question was would the CAP break or not with temperatures surging to near 90ºF in most of Iowa. It felt more like summer (July) than late-April. However, thanks to moistening through the afternoon the lid on the atmosphere finally got blown off by early evening. All the instability was quickly released. This was one of the easiest boundaries to find on visible satellite as well as CU started popping near 3:00pm with convergence along the front.

Morning sunrise as I pack up the chasing gearThe earliest rainbow I've ever seen as I caught this one at 6:00am

Cb's beginning to form as initiation is about to begin

Severe thunderstorm develops near Thornton, IA crossing I-35

Cloud bases a tad too high on this day for tornadoes and a more unidirectional wind profile

I-35 once again as the storm produces quarter inch hail to my north

Supercell characteristics at this point, but notice the lack of strong inflow to the left (Click to enlarge)...

After looking supercellular for a time the strong forcing along the cold front cuts off the best cell of the day

Another photo illustrating the high-bases on these storms

I decide to punch through the cold front to get a taste of the lower humidity

U.S. 20 as a new convective tower forms and also notice the fairly erratic jet contrail as pilots try to navigate and punch through the line

Not a great day for tornadoes, but an excellent day for photographing severe thunderstorms. I'll take it for the relatively short drive to north central Iowa.