Wednesday, June 26, 2013

Ryan's Storm Tour Of The Plains

Recently I wrote about why the Great Plains sees storms that are more severe than what the rest of the country sees. And in that article, I talked briefly about the three main types of thunderstorm – the single cell, the multicell, and the supercell.

But just reading about these types may not present the clearest picture. Thankfully, I now have actual pictures to present that picture. Get the picture?

I took all of these photos on my university’s Convective Field Study program – an 11-day storm chase that is treated more like a forecasting exercise than a traditional storm chase. I’m not the best photographer, so bear with me, but hopefully these shots from places where you can actually see the entire structure of a storm without hills or buildings in the way help to illustrate what severe convective weather really looks like.

First up is the single cell.

This thunderstorm was actually a bonus storm that we intercepted near Goodland, Kan. on the way back from chasing in Colorado. Notice how it is a single isolated updraft (in the foreground, at least).

Also notice that it has a rather high base. This can be a bit tough to judge, since bases will look higher the closer one is to a storm. But I’ll assure you that this particular storm base was at least 2000 meters above the ground, which is quite high.

Also notice how the cloud extends almost straight up from the base. This indicates that the storm was in an environment with very little vertical wind shear. If there was more shear present, the cloud would be tilted with height, instead of looking like a pillar like this one did.

Picturesque as it may be, this storm is known as “pulse type” convection. Single cells like these will form in unstable environments, perhaps become very briefly severe, and then succumb to their own cold outflow choking off the storm. This type of storm is most common in tropical regions, or in the Mid-Atlantic when the atmosphere feels tropical, with high instability and moisture and little to no wind shear.

Next up is the multicell.

This photo is particularly bad, because I took it through a car window while speeding down a highway in northeast Wyoming.

As its name probably suggests, notice that the multicell has multiple cells – in this case, three or four miniature updraft cores. Multicell thunderstorms like this typically also occur in the same high-instability low-shear environment as single cells do, except that in this case, there is some forcing mechanism like a cold front that is causing multiple updrafts to form instead of just one rogue one.

A squall line is a particular type of multicell thunderstorm. This photo of what is known as a “shelf cloud” comes from just north of Garden City, Kan. Strong outflow in this complex of thunderstorms forces the clouds out in a bow shape (if you were looking down from above) and produces a solid wall of clouds, that can often look quite threatening.

But this “wall of clouds” is not to be confused with a wall cloud – a feature that is unique to that third type of thunderstorm, the supercell.

Supercells are a much larger, more powerful, and longer-lived version of the single cell. They maintain themselves for much longer because they only exist in environments with sufficient vertical wind shear.

Notice that the storm here, from northeast Colorado, is not narrow like the first one. It is just as wide, if not wider, than it is tall. Although the “tilt” may not be obvious, this storm’s updraft is in fact tilted with height, which helps keep the storm alive for much longer.

Also notice that in the photo above, the top of the cloud looks “crisp.” This is an indication that the storm is healthy and still strengthening.

Later on, the same storm began to weaken. Notice how the tops of clouds looks “fuzzy” now. The correct term for this characteristic would be “glaciated,” but we’ll just stick to “fuzzy” for now.

The best part of all of this is that the same storm types, the single cell, the mutlicell, the shelf cloud, the supercell – both crisp and fuzzy – are happening right over our heads (and look to continue forming right over our heads for the foreseeable future, according to the forecast). We just can’t see all of this spectacular structure because of other non-meteorological factors. But trust me, it’s all there.

And now hopefully you have a better idea of what meteorologists mean when they talk about different types of storms.