Impressive roll cloud over Lake Michigan

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Stephen Davenport

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Jul 4, 2016, 8:22:08 PM7/4/16
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This was doing a reasonable impression of a Morning Glory last week:

Link: (YouTube)



Stephen.
Indianapolis, IN.

Dave C

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Jul 5, 2016, 4:29:28 AM7/5/16
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Incredible! Never seen that before. Nice to see the people on the beach observing it as well.

Dave C

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Jul 5, 2016, 4:32:10 AM7/5/16
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I forgot to say - what causes it Stephen?

Richard Dixon

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Jul 5, 2016, 8:15:04 AM7/5/16
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That's terrific - the evaporation of the cloud in the descending rear of the circulation is excellent. Is it precipitating in the distance right at the end of the video or is that just the cloud in the far distance?

Richard

Stephen Davenport

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Jul 5, 2016, 3:27:27 PM7/5/16
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Dave,

It's an undular bore, in this case generated by a line of of thunderstorms that had quickly developed across the far north of Michigan during the late afternoon of Sat June 11th. These shot out cold air downdrafts, so it's like a shelf cloud but becomes detached from the responsible supercell. You're seeing warm, moist air forced upwards and condensing (you can see the uplift on the front side) then rolling back down under the peak of the wave (imagine with a flick of the wrist sending one wave along a long skipping rope). If the air is not moist enough then these waves can develop without being visible except perhaps as a thin outflow boundary on radar..

There's still a bit of uncertainty regarding the precise mechanism in these circumstances. It's worth looking up some information on the Morning Glory that crosses the Gulf of Carpentaria, though - it's the one roll cloud in the world that is relatively predictable, being a result of Cape York sea-breezes interacting with the trade winds from September to November.  

Here was the radar (with obs) at 22:00z (18:00EDT) on June 11th (the video was shot at Empire, MI).



If I can find a good archived satellite picture then I'll post it.



Stephen

Stephen Davenport

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Jul 5, 2016, 3:44:19 PM7/5/16
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On Tuesday, July 5, 2016 at 8:15:04 AM UTC-4, Richard Dixon wrote:
That's terrific - the evaporation of the cloud in the descending rear of the circulation is excellent. Is it precipitating in the distance right at the end of the video or is that just the cloud in the far distance?

Richard

=======

It looks like it, doesn't it? I'd be a bit surprised, though. 

Here's possibly a better view - no precip apparent. I think in the first video it's an illusion brought about by the cloud and crepuscular rays.



Stephen.

Stephen.

Dave C

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Jul 5, 2016, 5:05:55 PM7/5/16
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Thank you Stephen. I kind of understand it ! A wonderfully spectacular phenomenon.
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