A Mesoscale Convective Vortex (MCV) developed yesterday out of a Mesoscale Convective System (MCS) in northwest Illinois and tracked near Detroit before moving into Canada. These rare meteorological circulations are pretty to see on radar and develop when the MCS (a collection of thunderstorms forming into a line and appearing circular on satellite) is powerful enough to create its own low pressure center with cyclonic circulation. Here is a radar animation (download AVI loop) of yesterday's MCV:
I'm surprised that the 4-KM WRF computer forecast model was able to predict the generation of the MCV (the high-resolution model routinely predicts individual thunderstorms and lines of storms, though it doesn't always get them in the right place), though one could argue that some of the last data to be input into the model before its 12Z run had the beginnings of the MCV, which appeared to start around 4 AM. Here's what the prediction (download AVI loop) for 18Z (1 PM Central Time) looked like:
The model was off on the timing considerably, having the MCV near Detroit at 1 PM - actually it passed over around 10 AM, and the placement of it was too far south. Still, the 4-KM WRF continues to impress me.
The National Weather Service, by the way, confirmed this was an MCV through their AFD (Area Forecast Discussion) products. At 415 AM EDT when it was just beginning to form, the NWS in Detroit hypothesized about their severe weather forecast for the day "THE ADDED TWIST OF AN MCV WOULD PROVIDE THE LIFT NECESSARY TO TAKE ADVANTAGE OF ANY INSTABILITY THAT BUILDS UP DURING THE MORNING HOURS." At 125 PM EDT the NWS in Gaylord, Michigan stated "DECAYING MCS NOW ROLLING THROUGH SRN LOWER MICHIGAN THIS MORNING WITH A WELL DEFINED MCV COMMA HEAD CONFIGURATION SPINNING IT/S WAY ENE THROUGH THE CENTRAL PART OF THE GRR CWA (Grand Rapids County Warning Area)". At 416 PM EDT the NWS in Detroit mentioned "MCV OVERHEAD."
The storm caused numerous severe weather spotter reports including heavy rain, flooding, downed trees, and a 46-mph gust in Detroit. It also aided Michigan's drought situation. By the way, the MCS itself was beautiful on satellite the night before:
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