Persistent Thunderstorms
Saturday Morning Thunderstorms
A steady parade of thunderstorms marched across southern Lake Michigan in the hours preceding the start of the 2022 Chicago Mac. (Click here for an animation of composite reflectivity radar imagery from 2:00 am CTD (0700 UTC) to 9:00 am CTD (1400 UTC.) In a preview of the things to come, a pair of severe weather events occurred during this pre-race period.
An Early Morning Downburst
At 4:40 am (0940 UTC), the Harrison-Dever Crib near downtown Chicago (NDBC Station CHII2) recorded a northeasterly gust of 62.2 knots. Sustained winds at the time were nearly 50 knots. The base reflectivity radar image at 4:26 am (0926 UTC) (Figure 15) marks the location of CHII2 with a small red dot and the storm responsible for the downburst to the northeast (click here for an annotated image). The base velocity radar image at the same time (Figure 16) shows a pocket of high winds (shaded in bright green) headed toward the radar station (click here for an annotated image). (Click here for a primer on interpreting reflectivity and velocity radar imagery.)
Waterspout!
At 6:22 am CDT (1129 UTC) the Milwaukee NWS office issued Marine Warning #29 (click here) for a possible waterspout approximately 20 miles east of Racine. A review of the base reflectivity radar image at 6:33 am (1133 UTC) (Figure 17) suggests a long-lived supercell thunderstorm was responsible for the possible waterspout (click here for an annotated image). In contrast to fair-weather waterspouts that typically form in autumn, waterspouts associated with supercell thunderstorms are true tornadoes over the water. They tend to be longer-lived, faster-moving, and more destructive than their fair-weather cousins.
Figure 18 shows the storm-relative radar data at 6:33 am (1133 UTC) from the Milwaukee NWS station. Storm-relative radar imagery subtracts the overall motion of the thunderstorm from the velocity field to highlight small-scale circulations, such as a waterspout, that are imbedded within the storm. The image shows the signature of the possible waterspout – adjacent areas of outbound and inbound motion suggesting rotation --that prompted the Marine Warning (click here for an annotated image).
Round One – Saturday Evening
The first round of thunderstorms reached Lake Michigan around 6:00 pm (2300 UTC) and persisted until approximately 10:00 pm (0300 UTC). Click here for an animation of radar imagery for the round. Figure 19 shows the fleet was approaching the border of Illinois and Wisconsin and directly in the path of the convective cluster which was travelling southeast.
Round Two – Saturday Night
The second cluster of thunderstorms reached Lake Michigan around 10:00 pm (0300 UTC) just as the first cluster was reaching southwestern Michigan. This second cluster continued until approximately 1:15 am (0615 UTC). Click here for an animation of radar imagery for this round.
Round Three – Early Sunday Morning
The third, and final, cluster thunderstorms arrived at approximately 1:15 am (0615 UTC) and lasted until 5:30 am (1030 UTC). Click here for an animation of radar imagery for this period.
