How to ID a supercell on radar?

[Allan Jeffers]

Recently I have started to wonder what a supercell thunderstorm looks like on a radar. I did a google search but did not come up with anything, perhaps I did not use the right terms?

So, what does a supercell look like on a radar map? Can you tell from a static image or do you need an animated loop?

 

[J Allen]

Hi Allan,

The primary definition for a supercell is a persistently rotating thunderstorm, as I am sure you well know. Now in some cases you can eyeball the rotation off regular radar but its not very accurate and usually requires strongly structured storms (ie hold their shape while rotating).

One common approach to identify supercells in the US is to look for evidence of a mesocyclone, so therefore you want velocity scans of the storm. Typically mesocyclones are identifiable by the couplet structure: that is a field of wind vectors going away relative to the radar, and a field going towards...usually these are delineated by colour so hence you have a pair of bright colours in close proximity. Depending on who you listen to these need to last a certain threshold time...usually 20 minutes is bandied about. This approach isnt foolproof however, as a downburst from a thunderstorm or strong outflow or even topographic flow modification can generate a similar appearance. So in order to confirm your suspicions you usually need to check out reflectivity. Another thing that can mislead with this approach is that cells in a low-topped environment may not show accurate mesocyclones to a sufficient depth to be identifiable.

On reflectivity (depending if you have vertical scans using something like GRLevel 2A or something), there a few shapes characteristic of supercells:
- A kidney bean shape, where the area of rotation is in the front flank of the cell. This is the idealised return for a HP supercell.

or

- A very dry appearance or limited return with an area of strong rotation when you know there is convection, this can be an LP type storm. (can be misleading in weak storm environments). No real good example as they can look like anything, but yesterday in Woodward there was a case so have a look through the nowcast thread.

- A pendant or hooked appearance to a cell, this is the classic type storm and the type of return you see regularly atm.

Another point to remember is these are idealised radar images of supercells, clearly there can be massive variation from cell to cell as you can see from the HP example above...and of course the spectrum between LP and HP is continuous rather than discrete so bare that in mind

Now in Australia, we don't have the luxury of a grid network of doppler radars the areas which storms occur, and generally they are only available in capital cities. We also have a slightly different steering environment, so unlike the US where you can get right movers basically following steering, we get very strong deviant motion....so down here we look for the odd cell out...that cell which changes direction as much as 90 degrees to the flow of crapvection.

Have a look at this page, it goes into a touch more of the reasoning on this identification of supercells:
http://www.theweatherprediction.com/habyhints/237/
http://www.theweatherprediction.com/radared/radarfaq/
http://www.theweatherprediction.com/radared/radarfaq2/

HTH

 

[Allan Jeffers]

This is why I was asking:



I am still pretty new to this. This cell was at a distance, I did note what I would call an "overshooting top" and near the bottom, it kind of looks like a "beavers tail" to the south of what I suspect is the main updraft area. I am looking to the east

 

[Chris Vagasky]

When/where was that picture taken?

 

[Allan Jeffers]

When/where was that picture taken?

4/19/10

I took this up near Tower road and 48th here in Denver. I am looking east

 

[J Allen]

Hi Allan,

If you can find the radar archived data for that particular day/location, I am sure people would be more than willing to help out with explaining what you are seeing (if anyone else can find it I would appreciate it, I don't know where to find NWS radar or other radar archives). At a glance the shear doesnt appear to be particularly strong...the updraft isnt that potent to completely overcome shear (the storm does not appear to be tilted a huge amount in order to create a Bounded weak echo region). Its more than likely a supercell or mature severe pulse storm though, give the inflow banding at upper levels, and mid levels, the relatively crisp backshear and the overshooting top (which you correctly identify) along with a single updraft. I would need to see either base features (which aren't really visible above), or radar images in order to offer a better opinion.

 

[James Gustina]

Doesn't look like a supercell from the radar archive on wunderground but the speed of the loop is so fast it's hard to tell. I'd still stick with pulser severe storm. Here's the loop by the way:

I will say that's an amazing photo though, supercell or not.

 

[Allan Jeffers]

Thanks all.

If you are interested here is the 5 frame panorama I made of those puppies (sorry for the strip mall, but I was at work)



Click for larger view

 

[J Allen]

Ahhh, now we have the full intel, thanks James.

Clearly not a supercell, probably a severe pulse storm which transitioned into a weak multicell (your pano and the radar confirms this).

Notice on the radar loop how none of the cells are long-lived or persistent, and in no way do they look like the radar captures above? Also notice the multicell phase, where there is no realy red returns just a weaker mesh of cells? You can see it from some of the earlier systems on the day doing the same thing...I would argue that the convective mode was severe pulse storm until some form of boundary/forcing arrived and switched things to multicell. This type of environment doesnt have alot of vertical wind shear (as we could see from the updraft being pretty much vertical), but does have a fair amount of instability (ie CAPE).

Still, a nice picture, and a nice pano as well. Well done.

 

[James Gustina]

I'd agree, wonderful cluster shot. And yeah J hit the nail right on the head. The storm's updraft not being tilted from vertical shear turned it into a briefly dominant pulser. Then since there was no separation from cooled air(downdrafts) and the updraft it probably was snuffed out pretty quickly.