Does the LCL determine whether a storm will be elevated or surface based?

[L Dobson]

Lets say the LCL is sitting at around 850mb or lower does that mean that the storm will be surface based or not? Is there a general mark that determines this?

And if not, what does determine if the storm will be elevated or surface based?

 

[JeremyS]

I'm going to explain how I use LCL heights and determining surface based convection chances. It's not going to be real technical but hopefully will make sense.
LCL heights themselves don't determine surface based convection. I look at those numbers for cloud base heights and for tornado chances I want those numbers to be 1000m or lower.
For me to determine though whether a storm will be surface based is to look at the LFC height and also the CIN numbers and the sounding itself.
If the LFC(level of free convection) is much higher than the LCL, than the storm won't be surface based. If the CIN number is normally above 50, than it's going to be pretty hard for a storm to be surface based. You can have LCL heights above 1000m and still have surface based convection, storms are going to have higher bases though. I've posted some examples below.

This sounding should produce elevated convection. You can see the LCL is very low, however the LFC is much higher. That is the layer where storms should actually form if they even did, as you'll notice the strong cap with CINH of -211, showing a strong surface inversion.


Here you can see a good example of a surface based sounding. The LCL and LFC are basically the same with no CINH. Storm bases would be very low with this sounding and would be surface based.


Here's a sounding where convection should be surface based as LCL and LFC levels are basically the same and there isn't a strong inversion. However, the dewpoint and temperature are far enough apart the LCL heights are higher, so the bases of the clouds would be higher(above 850) so tornado chances would be lower with this type of sounding(not to mention shear is horrible on this sounding too).

Hope this helps!

 

[Bob Schafer]

To begin with, I pretty much agree with everything Jeremy said. I'm going to add some stuff I believe I've learned from a lot of years of chasing, but I'm not a meteorologist. I only say that because I know you don't know me.

One thing that I learned a long time ago, not that it's necessarily correct, is that a storm being elevated vs. high based is two completely different things. Being elevated means that it is not surface based, period, which at the same time says that the storm exists only above the cap. You can have days when there is no cap at all, but then you're not going to have any "storm" anyway. You'll have rain. Okay, so let's say you have an elevated storm. What happens next? Either it stays elevated, or it becomes surface based.

Have you ever chased a storm early on in its lifetime? I would say most supercells start out elevated, and it's usually really easy to know that they are. It's because they start out racing along at the speed of the midlevel winds. During that early phase, I watch with anticipation for the storm motion to come to a screeching halt, and it'll happen at the same time that the storm base comes way down. Good chance you'll get a right turn here also. Game on.

This is the part where the LCL matters, because now it's surface based, i.e. the updraft is being fed by the PBL. Elevated storms ingest no PBL.

I'm probably really asking for an argument here, but I sincerely believe that most of the time the cap breaks from above, not below. It is broken when an existing elevated updraft sucks a hole in it from the low pressure at the base of the upraft. Is that helpful?

 

[Taylor Wright]

Great points from Bob and Jeremy. I'd say there is a lot of confusion regarding elevated vs. high based as they are two different things as Bob mentioned but can look fairly similar visually. Most importantly you want surface-based and low LCL convection for tornadic storms so the supercell can ingest the low level vorticity and pinch it downwards via an RFD. There are rare cases where you can get tornadoes with high-based cells without an RFD if there is enough pre-existing surface vorticity and a strong enough updraft to stretch the vorticity upwards (land/waterspouts).