Thursday, June 18, 2009

Tornado Watch 'til 11 pm, possible MCS later?

Update: 7:45 pm. The longer I look at the pattern the more I'm starting to believe we're looking at an MCS scenario. An MCS is a "mesocyclonic system", a swarm of severe thunderstorms that tends to intensify at night, producing straight-line winds, torrential rains and (sometimes) almost continuous lightning. These MCS systems are fairly common in June and July here in the Midwest, forming on the northern edge of an expansive dome of hot, humidified air. I'm not minimizing the tornado risk, but I have a strong gut feel that we may be looking at a different feature later tonight, with the best chance of severe weather/torrential rain from 10 pm to 1 am or so, possibly arriving after 9 pm in the St. Cloud area. The tornado watch remains posted until 11 pm, but my hunch is that this watch will transform into a series of severe storm watches later tonight as an MCS system gets going and intensifies as it approaches the Twin Cities, Rochester and Mankato. Stay tuned...

Latest visible satellite image showing the tops of thunderheads being swept to the north and east. There is an extensive area of heavy weather moving in from the Dakotas/Red River Valley, and a significant potential that these storms will mutate into a boomerang-shaped MCS as the night goes on, with a possibility of damaging straight-line (and tornadic) winds, and torrential rains capable of street and stream flooding.

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