About those clouds over Wrigley

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Twitter: @CubsWhen I first saw the images of those scary-yet-pretty mammatus clouds hanging over Wrigley Field Monday night, I of course thought, “Wow, I have to write about this for The Rainout Blog.”

But, wait. What do I write? I’m no cloud scientist.

But you know who is? Dr. Robert Houze, professor of atmospheric sciences at the University of Washington.

I asked Houze Wednesday, via email, to describe mammatus clouds and tell us what non-experts, like you and me, can interpret from those clouds.

I lofted a few softball questions at Houze, such as: Do mammatus clouds mean sever weather is imminent? Or, perhaps, can we determine from their presence that the threat of bad weather has passed?

“It could be either, but more commonly they precede the severe weather,” said Houze, recipient of the 2014 Symons Gold Medal of the Royal Meteorological Society. “They occur on the underside of upper level clouds extending out from the thicker raining cloud. The upper level clouds on the leading side of the storm are more extensive, so it is more likely that the storm is approaching.”

Severe storms had swept through Chicago earlier in the day, which caused flooding in some parts. According to reports, those mammatus clouds – which often are “emanating from a strong nearby thunderstorm,” Houze said – appeared in the Windy City between 8 and 10 p.m.

As Houze suggested, fans watching the Cubs and Dodgers at Wrigley could have determined from the clouds that more storms were approaching.

They could have used that sign in the sky to grab their umbrellas and practice draping themselves with ponchos because, sure enough, another round of storms swept over the city and rain doused the ballpark.

Chicago was under a tornado watch much of Monday as strong storms swept through the Midwest. Nine tornados were confirmed by the National Weather Service to have touched down in Illinois that evening.

The sight of mammatus clouds lead many to believe there is a strong chance of a tornado.

“The clouds that produce strong tornadoes are called supercell thunderstorms, and supercells often feature very pronounced mammatus,” Houze explained. “Of the supercell storms that occur, only a few actually generate a tornado whereas many produce mammatus. Therefore it is possible that a tornado may be in the vicinity but not certain.”

The professor, who is a sports fan of “sadly the Mariners, but more happily the Seahawks,” said mammatus clouds are not always associated with supercell thunderstorms. However, “such storms provide the best examples of this type of cloud.”

Houze said mammatus can occur in many of places, “but supercell thunderstorms are most common over the central U.S.”


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