Please download the latest version of Java Virtual Machine from http://www.java.com if you're having trouble viewing this loop.

Loop shows base reflectivity from the WSR-88D in Des Moines, IA from 16:03–19:01 UTC on 29 June 1998. This time period was selected to capture the developing MCS as it moves into radar range. The loop ends when the radar failed just after 1900 UTC due to a lightning strike. The radar was not repaired until after the event.

An office is asked to first describe the loop and then discuss the potential for severe weather. The following features should be noted: 1) the evolution of the system from isolated convective cells to a squall line to a squall line with trailing stratiform precipitation; 2) the formation of a vigorous cell ahead of the line at 17:01 UTC and its merger with the line around 17:46 UTC; 3) the formation of a hook along the leading edge of the line as it approached Des Moines. This hook is clearly visible at 18:33 UTC and is associated with the part of the storm that underwent the merger with the vigorous cell just described; 4) the development of a trailing stratiform region beginning around 18:00 UTC; 5) as the loop ends, maximum reflectivities decrease slightly; and 6) in the last few frames of the loop, two notches form along the trailing edge of the deep convection.

The potential for severe weather is high throughout the loop. For most of the loop, the main threats appear to be hail and tornadoes associated with high reflectivities and hook echo, respectively. Towards the end of the loop, the main threat appears to be strong winds as the leading line consolidates and notches form, indicating the possible development of a rear-inflow jet. Localized flooding is also a threat.

The class is informed that large hail and three tornadoes (F1, F2 and F2) were observed including an F2-tornado associated with the hook echo. Strong winds were reported over widespread areas. These reports were more numerous and intense as the line passed over Des Moines. Small stream and urban flooding were reported over isolated locations.