Essentially, there is no such thing as a snow-producing supercell. It's meteorologically impossible. Those photos show typical shallow winter convection.supercell—An often dangerous convective storm that consists primarily of a single, quasi-steady rotating updraft, which persists for a period of time much longer than it takes an air parcel to rise from the base of the updraft to its summit (often much longer than 10–20 min).
Most rotating updrafts are characterized by cyclonic vorticity (see mesocyclone). The supercell typically has a very organized internal structure that enables it to propagate continuously. It may exist for several hours and usually forms in an environment with strong vertical wind shear. Supercells often propagate in a direction and with a speed other than indicated by the mean wind in the environment. Such storms sometimes evolve through a splitting process, which produces a cyclonic, right-moving (with respect to the mean wind), and anticyclonic, left-moving, pair of supercells. Severe weather often accompanies supercells, which are capable of producing high winds, large hail, and strong, long-lived tornadoes. See also convective storm, thunderstorm, splitting convective storm, cell, bulk Richardson number.
If it was earlier, it's only by an hour. My phone was in MST when the picture was taken, but could have been on PST.2. Jody, do you mean that the time was 0037Z March 1 (i.e. 5:37 MST Sunday, Feb 28)? Looking at the radar archive, it doesn't seem to show much snow shower activity near Truchas - seems to be a bit farther southeast at that time. Could the photo have been taken earlier than that?
Thanks for posting the sounding information, Jeff. I would agree that those parameters would seem pretty weak for a supercell, although I am not entirely sure exactly what it would take in a cold environment.I suppose theoretically it is "possible" to get a supercell that precipitates only snow, but it would very VERY unlikely. You'd have to have temperatures aloft to be cold enough to get enough CAPE to get a strong enough updraft to generate such a storm. The Albequerque, NM sounding from 00z 1 March shows only 145 J/kg of SBCAPE, but less than 20 kts of 0-6 km shear and less than 20 m2/s2 of SRH. I doubt such instability and shear could create a supercell. Not to mention, the freezing level was 3300 ft AGL, so any actual snow falling from under the cloud base would certainly have melted into rain or evaporated completely by the time it reached the ground. So technically, that wouldn't even be a snow-producing supercell.
Just wanted to clarify - you realize that a storm has to be rotating in order to be a supercell? Being low-topped and with good structure is not enough, it must have persistent rotation.That said, other than the rotation, I was assuming that a snow squall could in fact be a low top supercell.
And that's the key.Just wanted to clarify - you realize that a storm has to be rotating in order to be a supercell? Being low-topped and with good structure is not enough, it must have persistent rotation.
Any radar examples? I just don't see the ability for a full-fledged supercell with snow. Could there be a little spin in a snow squall? I'd say so. But persistent? Doubter until proven otherwiseAlmost for sure, low top supercell convective snow squalls due occur in Michigan and other great lake states
There are plenty of tornadoes that can be produced by non-supercell convection. Hell, you can get vorticies in clear air. If you get a tornado touching down along a lake shore when there is such a temperature gradient as to get convective lake effect snow, I sense there is a non-supercellular, non-mesocyclonic entity at work. I must agree with Mr. Dale and remain a skeptic until shown a concrete example.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.
That sounds likes a challenge! I will keep my eyes open for an example going forward.Any radar examples? I just don't see the ability for a full-fledged supercell with snow. Could there be a little spin in a snow squall? I'd say so. But persistent? Doubter until proven otherwise
I think when you are talking about "sleet" in regards to lake-effect..I think you are really talking about "graupel".I live on the coast of Lake Erie, where we get some pretty spectacular winter convection from time to time. Thunder snow/sleet is not uncommon here. I've always wondered about something like this, and this is how I've got it figured from my limited forecasting experience.
Convection can occur at any temperature, you only need an appropriately strong vertical temperature gradient. For a supercell, besides that convection, you need moisture (a problem in winter but not impossible. Lake effect, for instance) and a properly sheared wind field. If any of you guys have ever looked at a really wicked winter storm, the hodographs are often some of the most beautiful and deep curves I've ever seen, so I would think that's also possible. There are lots of other variables, but those are the big ones, so just for argument's sake, lets say it is theoretically possible.
My one big question is, given the fairly vigorous nature of the updraft in a supercell, even if the entire storm existed in a below-freezing environment, would it really be snow? I would almost think that the updraft would result in sleet or some other form of heavier precip, though I suppose if some of the precip formation happened closer to the top of the storm, it might not be quite so nasty an environment for a delicate snow fake, and could result in some snow/sleet/hail mix.
I've seen some pretty spectacular thunderstorms producing copious amounts of sleet, complete with CG and a gust front. What says it couldn't rotate in the right wind fields?
As an interesting side note, in December we had a pretty nasty winter storm come through. It went from the high 40s to the low 30s in less than 2 hours. A tornadic supercell fired on the leading edge of the cold front, just inside the warm sector, followed closely by a *violent* squall line that produced hail, sleet, and rain, along with tons of lightning and winds approaching 70mph. In the cold pool below the squall line, temps dropped into the low 40s/high 30s almost instantly. Pretty spectacular cold core sort of setup