Low top supercell convective snow squall

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Jan 28, 2005
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Haslett, Michigan
Here is a link to some photos of some impressive Winter type convection in Britian with snow being the primary form of precip..complete with well defined anvils and even some good mammatus clouds! The link includes radar images of a convective snowshower that containing severe/damaging hail/high winds.(that particular cell..concluded with heavy freezing rain.)

http://www.eots.co.uk/reports/Xmassnow/Xmassnow2004.htm
 
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I think the recent event near Tinian, NM (discussed in a recent thread in the Weather in the News section) is relevant to this discussion from some years ago. I know the majority opinion is that this tornado associated with a snow squall was a landspout, not a mesocyclone tornado, but looking at the video and seeing the tornado clearly separated from a nearby precipitation shaft, I am not so sure. And regardless, it certainly shows you can get rotation, and even a tornado, with a New Mexico snow squall.

 
Here in the UK, it's possible to get 'low-topped' supercells in cold airmasses in strongly sheared environments. I certainly know of examples whereby the air temperatures were only around 6-7C or so. Regarding snow, though, it's harder to think of an example. It's possible to have such a storm which produces intense precip and lowers the wet bulb freezing level enough to get snow to fall to ground level, I think - but to have one which *only* produces snow would be a bit of a tall order - at least in the environments I'm thinking of over here.
 
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Nick Dewhirst

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Aug 18, 2018
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Novi, MI
Almost for sure, low top supercell convective snow squalls due occur in Michigan and other great lake states.

There is no doubt that the proper ingredients such as moisture, shear and CAPE would be in place during the cold season near the lakes. The lakes can generate tremedous CAPE from heat/moisture coming off the lakes and very steep lapse rates. (Just take a look at BUFKIT soundings during the late Fall. 1500-2000 lake induced CAPE values happen) Proper shear is more difficult to obtain because it would tend to spread available moisture out too much and weaken convection. Also adequate shear would generally cause lake induced convection to quickly move away from its source of heat/moisture so persistence requiements of a supercell wouldn't be met.

I can think of at least one situation where something like this would mostly likely occur.

Consider Lake Superior and the North shore of the Upper Pennisula which runs basically in a West to East Fashion. NW winds coming off Lake Superior..supply a continous supply of the required heat and moisture...and a West to East boundary that exists inland from the Lake caused either by a lake breeze or some other type of localized convergence..could create a persistent low topped supercell moving along the boundary.

Is there an example of this? Per "Michigan Weather" by Richard A. Keen...in 1987. "A lake-effect "snowburst" dumps 27.5" of snow on Munising on April 1-2, burying cars in 6-foot drifts. Less than 40 miles away at Grand Marais, only 1" of snow falls. As the storm gears up on the afternoon of the 1st, a brief tornado drops out of a snow squall and damages a mobile home on the south shore of Whitefish Bay".

Couple of things to note about this. The tornado is at least suggestive of a supercell. I don't think that this tornado would have been of the waterspout variety as Whitefish Bay would have likely still been completely froze over on April 1 and the South shore is at least 25 miles from Lake Superior. Munising and Grand Marias are in a line West of Whitefish Bay. Another likely necessary ingredient..no snow on the ground. Afternoon heating on bare ground would definately help the cause for more scattered/intense convection.
Living in Michigan I may be a bit biased, but I see where Mike is coming from, as the ingredients can be there fairly often during the cold season. However, I think it’s more likely that mesolow moved off of the lake and an intense feeder band followed, sitting over Munising for hours on end. Scenarios like this can produce 3-5 in/hr snows, and I saw similar setups a few times last winter over Lake Superior, Michigan, and Huron.

The winter weather in Michigan is definitely some of the most difficult to forecast considering the lakes affect/amplify most storms that come through. I still think a snow-producing supercell could form, but it’d have to be a winter extreme.
 

Nick Dewhirst

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Aug 18, 2018
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Novi, MI
These "mesovortices" features over Lake Ontario do have a supercell look to them although it appears their formation is quite unlike supercell formation. Unraveling the mysteries of deadly 'firehose' lake-effect snow eventsView attachment 19151

These structures even have BWER features:
BWER Lake Effect

This type of feature literally produces rotating intense vertical fountains of snowflakes over the lake.
I feel like it's almost as if the rotation suspends snowflakes similarly to hail from the true supercells, maybe leading to a large flake size/clumps? The rotation is impressive to me considering the scenario.

The BWERs are interesting. Since snow is the lightest (in terms of weight) form of preceipitation, the updraft wouldn't need to be overly vigorous in order to produce a BWER in a convective snow band. Very cool pics, Mike.