05-03-2012 CHASE LOG: IOWA I was not expecting much out of this day as it was looking like the weaker severe weather day of the first 3 days of May for the Upper Midwest. However, I had vacation with no obligations and decided to wait at my parents in southern MN for anything to develop along a remnant outflow boundary that had pushed south to near the MN/IA border from morning convection to the north. I thought about leaving in the morning and heading south towards the main synoptic front that had settled in near the IA/MO border, but the tornado threat did not look all that great in my opinion, and I thought my chances for seeing at least severe weather were just as good close to home.
Around 2pm CT, a lone storm first developed near a remnant boundary intersection just to the north of Emmetsburg, IA. I jumped all over this storm, heading south on I-35 and then west on Hwy 9 and then continued west out of Forest City on Cty Rd A42, intercepting the storm near Bancroft. The storm was developing in an environment characterized by MLCAPE values near and exceeding 1000 j/kg and effective bulk shear on the order of 25-30 knots. A subtle shortwave was also noted on water vapor, per the mesoscale discussion issued by SPC at 2:12pm, that likely led to the isolated thunderstorm development. The MD also highlighted that severe hail would be possible, yet isolated enough that a watch may not be needed. A watch was never issued for this event.
Upon reaching the storm, it was apparent that the storms were going to be very slow-moving and easy to keep up with. I proceeded to drive back and forth, in and out of the hail core of this storm on Cty Rd A42 for several hours, mainly experiencing an abundance of dime to nickel sized hail and intense rain/hail rates. Some of the more intense hail I experienced right in the town of Forest City where there were reports of isolated hail near quarter size. The storm picked up speed a bit and, as you can see towards the end of the video below, I encountered some very intense winds from the storm near the intersection of 310th St and Grouse Ave about 4 miles north of Clear Lake. I continued to follow the storm east, moving right along the intense hail core, to near Osage before leaving the storm as it was quickly losing intensity as it moved into more stable air.
One of the few photos I took from the day as I focused more on video. Intense hail core ahead of me after I just crossed I-35 on Cty Rd B20/300th St to the north of Clear Lake, IA.
Storm forming a ragged shelf cloud as it began to weaken to the southwest of Osage, IA.