Downburst and Fake Wall Cloud

[kevin-palmer]

I was out yesterday photographing storms in Central Illinois. I was near Goodfield when this storm started forming. There must have been a strong updraft because there was a rain-free base for awhile at the beginning. Then a little bit of rain started to fall and that's when I started recording this time lapse. I shot a picture every 3 seconds for 12 minutes. At the very beginning I captured a wet microburst. I did a search and could not find very many other videos that showed a ball-shaped rain shaft such as this. But I have no idea what happened next. A lowering started forming out of the clouds that looked exactly like a wall cloud. But it was on the north side of the storm, instead of on the south side underneath the updraft. I sent this in to the local NWS office and it even stumped them. But they want to use the video for spotter training classes. Any ideas what I captured?

Watch video >


Wet Microburst by kevin-palmer, on Flickr


Fake Wall Cloud by kevin-palmer, on Flickr

 

[John Farley]

I am wondering if it could have been a storm split. Did new precipitation occur near or north/NE of the lowered area after it moved away from the original storm?

 

[Manuel Salgado]

I think its enhanced convection on the outflow boundary caused by the microburst. If you look at the other side of the storm you can see some clouds form on that boundary as well they just aren't as substantive.

 

[kevin-palmer]

I am wondering if it could have been a storm split. Did new precipitation occur near or north/NE of the lowered area after it moved away from the original storm?

Yes it did, rain started falling from where I was shooting. Do you think it's the base of a a very small updraft?

 

[John Farley]

Yes it did, rain started falling from where I was shooting. Do you think it's the base of a a very small updraft?

Yes, could be. Hard to tell from what I can see in the pics and video, but that looks like a possibility.

 

[Bob Schafer]

I believe the microburst was an RFD. The updraft was there the whole time, but not too strong/evident. The RFD rapidly changed the nature of the updraft's inflow, primarily raising the Td and dropping the LCL, causing the WC to form.

 

[Jeff Duda]

It would help to check SPC mesoanalyses at the time you took these shots to see if there was much shear to support the idea of there being any supercell structure. It doesn't look to me like there is - I didn't really see any storm scale rotation anywhere in the storm, but the mid-levels are obscured, so it may be there.

Given the manner in which the lowering appears and how the cloud fragments seem to pass through it, I'd say it's more like a shelf cloud than anything, just limited in horizontal scope. You can clearly see pieces of the lowering appear to enter from the right (i.e., away from the updraft) and exit to the left (going towards the precip). You can even see an ascent and descent through that feature, which is a textbook gravity wave structure.

By the way, a ball-shaped rain shaft is a classical representation/signature of a wet microburst. I'm pretty sure most spotter training classes will show you something like that.

 

[chrisbray]

There was pretty much no shear that day in Illinois, FYI

 

[Skip Talbot]

I "chased" several of these cells yesterday. I didn't see anything that indicated supercell structure, which an RFD would require. These were all warm sector pop up storms that quickly rained into their own updrafts.

Likewise, I don't see anything out of the ordinary with this shot either. I've seen subsevere showers with well defined wall clouds and tail clouds. A wall cloud is just an inflow based lowering feeding off of rain cooled air. You don't need a supercell to obtain one. Additionally, I don't think it's too unusual that the lowering is coming out of the north end of the updraft base. Since there wasn't any real shear, the storm isn't raining downstream to the north, simply straight down, so there's still going to be an updraft base on the north side of the cell, and this area could still develop lowerings from rain cooled air. Is it wall or shelf? It looks more shelf to me given that the feature appears to be kicked up by the outflow, the lowering conforms to the cold pool contour of the outflow, pointing away from the rain like a shelf cloud. You can see additional, smaller outflow based lowerings developing to the left as well. It may also be a partially inflow based feature feeding off the rain cooled air like a wall cloud too though. These cases under non supercells that aren't well defined though, I would simply call "lowerings" as I don't think it's really significant to distinguish whether they are wall clouds or shelf clouds.

This video is a great example of a non supercellular pulse storm though. I think it would be quite valuable for spotter training.

 

[calvinkaskey]

I think it is a gust front with accompanying shelf cloud.

 

[calvinkaskey]

http://www.youtube.com/channel/UCA4jcFFZtdlzLSexGqUhWMg or youtube "best funnel cloud video taken in New York in 2013" Shows what appears to be a thunderstorm connected to updraft so well it produces 3 rapidly developing funnels lasting 30 sec each but one looks like a f-2 or better (the first one in the back at the start of the video). Kind of shoddy but should be used all around as a spotter guide for funnel clouds. Took a month of me looking at it and then I found first funnel movement which would multiply the probability of more funnel clouds in the same area by like 10x or more.