| Episode Narrative |
A very unstable atmosphere was in place over Iowa with CAPE values around 2000 J/kg and lifted indices in the -8 to -10 C range. Precipitable water increased to around 2.25 inches along a boundary that extended from northeast into west central Iowa. Downdraft CAPE was in the 700 to 1000 J/kg range with 400 to 800 J/kg available in the -10 to -30 C layer of the atmosphere. The LCL was between 750 and 1000 meters. The freezing level was very high, around 16,000 feet. In spite of the relatively strongly sheared atmosphere, which was 35 to 45 kts, the thunderstorms had a hard time developing. A firm cap was in place with 700 mb temperatures of 14 to 15 C by early evening, and 500 mb temperatures of -4 C. Thunderstorms formed over northeast Iowa along the boundary. The thunderstorms back developed along the boundary well after sunset and became very efficient rain producers. The storms trained along the same line with a quick 2 to 3 inches of rain falling from west of Waterloo to near the Waterloo area. The rain fell in a short period of time, one to two hours, on top of ground that had received significant rainfall during the morning hours of the 22nd. This resulted in rapid runoff of water and flash flooding. The thunderstorms continued through the night with total rainfall north of Waterloo in the Denver area reaching 7.11 inches by sunrise. The line of storms back developed west across the state overnight. Heavy rainfall of 2 to 4 inches fell in a band extending west into the areas that saw flash flooding the previous day. Flash flooding was reported in Bremer, Webster, Wright, and Sac Counties. General flooding took place in many areas of Hamilton County as well. Severe weather was absent with the storms through the night. The tropical nature of the atmosphere limited the severe threat. |
