3/31/07 Reports WI/IA/IL/MO

[Ryan Pfannkuch]

very similar story to others...stubbornly sat along I-80 near Atlantic, IA for nearly 2 hours intentionally ignoring all of the initial development in eastern NE and far southwest IA. I was intent on sticking close to my 4-county target area (Audubon, Guthrie, Carroll, Greene) as I figured that eventually an arc of more isolated cells along the actual surface front/dryline extending from the mess southeast of Omaha would eventually move into my area. I was also ignoring the stuff going on north of I-80...as I was intent on "riding the last wave" northward. Sure enough, after plenty of waiting, this arc of storms formed...

The first TOR warned storm in eastern Guthrie Co. caught me off guard as it was a part of the "northern development" that I was ignoring. I did however start blasting east on I-80 at this time...and ended up in perfect position to intercept the second TOR warned storm as it crossed I-80 just west of Adair. In short, I followed this storm north for 45 miles on county highways from Adair northward through Coon Rapids, playing leap-frog with some other Nebraska chasers (not sure who), before finally letting it go north of Ralston. This storm showed a nice lowering at times, and maybe a little nub funnel every now and then, but nothing more.

I am a little surprised and a little perplexed with the lack of tornadoes on these storms in western IA, although I do speculate that the widespread initial "northern development" acted to hinder/cool down the thermodynamic environment for the last wave of isolated cells.

At any rate, at least logistically the chase was pretty satisfying, with 3 of my 4 targeted counties going under TOR warnings at some point. Just wasn't quite the right mix of ingredients today...

 

[Scott Olson]

Tageted Onawa, IA. Upon seeing the storms firing early than expected in SE Nebraska, I spent a little indecisive time re-looking over the data and deciding what to do. During this time I chased some weak cells nearby and then decided to bolt south. As I was heading south I noticed a cell had formed just north of the front and could be intercepted pretty easily near Blair. It didn’t look too strong but the cells that were firing to the east were looking linear and the velocity fields looked unimpressive, the stuff to the SW was somewhat decent but appeared to be on a weakening trend, so I went with the somewhat isolated storm. Six miles west of Blair I intercepted the storm, it had a FFD boundary and some nice CG lightning with a very stepped appearance to it. A small funnel like feature was present right before but seemed pretty inane. RFD started to cut in during this time and as cluster came in from the south I decided to head north and try and keep up with it. It was during this time that I started to notice subtle rotation on the radar and kept taking pictures. Despite my north driving efforts the rain started to come down but I managed to make a funnel cloud out prior. Several minutes later I could see a little better but another cell had gotten between myself and the tornadic cell, however the RFD cut was easily visible and I could see the lowering before being blocked by a small area of heavy rain. After 20 minutes in the rain I managed to get out and to my east I noticed a funnel dip down about a 1/3 of the way to the ground and then promptly go back up.

More at http://axisofnature.com/2007/

 

[cdcollura]

Good day everyone,

I was also out and about working the storms in the Des Moines, Iowa area area and managed to see some large hail, storm structure, and strong winds. The chase log itself is below followed by some pictures ...

Full chase log is here: http://www.sky-chaser.com/mwcl2007.htm#MAR31

March 31, 2007 was a chase day with severe thunderstorms intercepted in central Iowa near Des Moines near the Interstate 35 corridor. The chase began in the late-afternoon of March 30 leaving Dayton, Ohio and spending the night in Chicago, Illinois. The primary target was central Iowa and that area was targeted early on March 31. Left Chicago and headed toward Interstate 80 and crossed into Iowa by noon. Checked data and found the best possibility of severe weather near Des Moines. A warm front was draped south of the target area, with increasing moisture advection coming in from the south under an upper-level low approaching from the west. The problem with this type of setup was somewhat limited moisture return and, more importantly, having south-southwest winds aloft over southerly surface winds (not much directional shear).

The warm front intersected the cold front / dry punch to the west of the target area, creating somewhat of a "triple point" in west-central Iowa. Temperatures in this area were not very warm, and reached the upper 60's by the afternoon, yielding a surface CAPE of about 1,000 at best. Helicities were also highest in this region, about 150-200, enough for low-topped supercells with the differential vorticity and cold air aloft. Upper winds were strong, with at least 50 Knots of uni-directional bulk shear to 6 km (500 M and the exit region of an H3 jet stream moving in farther up ahead of a negative tilt ahead of the upper trough / low. Storm motion was to be very fast and with unidirectional shear, a plan for hail and severe winds were the agenda for chasing. At SPC, a slight was issued for the 16:30z outlook, with a rather high 10% tornado probability, 25% hail, and 30% damaging wind. A mesoscale discussion (MD) and subsequent tornado watch went up for the same target area.

The trip to the target area continued into Des Moines along I-80. Convection was first encountered about 5-10 miles east of Des Moines. A severe thunderstorm was intercepted in this area, and was part of a multicell line of strong and severe thunderstorms. These storms were intercepted at about 3:30 PM and allowed to move off very quickly to the northeast. Back west, some more storms developed closer to the location of the upper level cold core dry punch. One storm west of Des Moines was highly sheared and briefly LP supercell in nature. The dry punch quickly undercut this region by about 6:30 PM. No tornadoes were observed this day, but some small funnels were noted. The chase finished with a drive pretty much back east on I-80 then into Illinois where the nigh was spent again in Chicago. The drive back to Datyton, Ohio was done the following day. Total mileage was about 792 miles.

Mar 31, 3:30 PM - Penetration of a severe thunderstorm in Polk County, Iowa just north of Interstate 80 and near Altoona along State Road 945. The storm was pert of a multi-cell cluster of severe thunderstorms and contained lightning, torrential rains, winds near or exceeding 60-MPH, and hail up to nickel sized. Another small storm developed to the west of this area behind the line and had some LP supercell characteristics on the west side of Des Moines, Iowa. The storms were caused by a low pressure trough, surface heating, boundary interactions, and a strong upper-level low pressure area. A 2007 Ford Focus was used to chase the storms. Documentation was still digital photos and HD video. A tornado watch was also valid for this area until 7 PM EDT. Total mileage logged is 792.4 miles.

Above - Storms going up (low topped) east of Des Moines, Iowa looking west along I-80.

Interesting cell goes up just west of town. Note the small hail shaft to the left.

Interesting mammatus or mammatus-like clouds, most likely a result of intense DVA (Differential Vort Advection) east of Des Moines.

Double rain-bow ends the day in far eastern Iowa along I-80.