| Episode Narrative |
Following the convection of the morning, skies partially cleared during the afternoon across central into northern Iowa. This destabilized the atmosphere with CAPE rising to between 4500 and 6000 J/kg and lifted indices falling to between -9 and -12 C. by late afternoon. The atmosphere remained weakly sheared with about 20 kts of shear. There was plenty of cape available for hail production, between 600 and 800 J/kg, in the -10 to -30 C. layer of the atmosphere, but the freezing level was very high and was between 14,500 and 15,500 feet. Downdraft CAPE was between 800 and 1000 J/kg. The atmosphere was very wet with precipitable water values between 1.7 and 1.9 inches. Thunderstorms erupted quickly during the late afternoon hours over northwest Iowa. The storms struggled to become severe. Rainfall from the storms was very heavy with rainfall rates in excess of 2 inches per hour. This caused some local flooding. Minor flash flooding was reported northwest of Schaller in Sac County with creeks out of their banks and water flooding farm fields. Many of the storms produced pea size hail and wind gusts to 30 to 40 MPH. A rotating wall cloud passed over the town of Greene, in Butler County. There were spotty reports of severe weather. Penny size hail fell east of Algona in Kossuth County, and a 59 MPH wind gust at the RWIS site at Mason City. The storms weakened for a period of time. New thunderstorms fired up over the southeast part of the CWA in the late evening. One became severe and produced a wind gust to around 60 MPH in northeast Wapello County. |
