What is a tornado? As defined by the AMS... "A tornado is a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud."
What is not a tornado? Anything that is not referenced in the definition above. So is a gustnado a tornado? NO! Are landspouts tornadoes? YES! There has been debate weather or not a waterspout can be considered a tornado. True waterspouts develop out of cumulus clouds or rain showers predominantly in the FL keys. Certainly not a supercell, but fits the definition of a tornado (see ....from a cumuliform cloud....) There is a difference between true waterspouts and tornadic waterspouts. One forms from fair weather Cu and the other is most likely because a tornado in progress happened to move over a lake or other body of water.... Now that we strayed off topic I will attempt to bring us back on track.
So what is a tornado? How do you know you see a tornado when you are out chasing? Let me step on my soapbox for a minute..... I see a lot of people who have never seen a tornado before go out chasing and are quick on the trigger to call EVERY suspicious lowering a tornado. Adrenaline is going because you are near a storm you can't help but see things you aren't really seeing. I know, I have been there. However you need to calm down, take a step back and really think about this. Remember, most tornadoes will have a visible wall cloud present, but even before that... think about where you are looking in regards to the storm. If you are 5 miles N of a storm and are looking SE and think you see a tornado odds are you are looking into the core of the storm are seeing nothing but heavy rain which can have the illusion of a giant wedge. If you are 5 miles east of the storm looking west and see dust on the ground that could either be caused by A) outflow or B) a gustnado. If you are seeing a dark line of clouds with funnel shaped tendrils that appear to be rolling or rising in a rapid manner on the LEADING EDGE OF A STORM you are NOT seeing a tornado. There is a ton of turbulence involved with the leading edge (shelf cloud) of a line of severe thunderstorms. But let's even step back further.... if you are running mobile radar take a glance of what type of storm you are dealing with! If you chasing a messy cluster of severe thunderstorms and are NE of the multicell cluster, odds are you aren't going to see anything close to being reported as a tornado. You want to target supercells for tornadoes. Not all supercells will be isolated though. Many times storms will explode and merge and you may have LEWPs with embedded supercells. Those can be dangerous to chase because it will appear as a giant line of severe thunderstorms approaching but you may notice the shelf cloud curling into a specific region along the line. Look at your radar and velocities to notice if there is a notch in the line. I personally have never observed a tornado embedded within a squall line or LEWP. I know they exist and the closest thing I got to that was a bookend vortex tornado on 6/1/99.
Okay, now that we came to the conclusion that you are chasing a supercell. Let's move to where the best area is to observe a tornado. The BEST way to observe a classic supercell is by coming in from the south. Especially if this an isolated supercell. If you approach the storm from the north you would be core punching and not something a newer chaser may enjoy doing. If you are chasing the storm from the west then you F'd up because you let the storm get ahead of you. If you are chasing it from the east looking toward the west, odds are is that you will be looking straight into the core. So the best option for chasing a tornado would be south of the rain/hail in the clear air. Visibility will drastically improve and depending on where you are on the plains, you will have a view for 10's of miles. So now that you are "approaching a rotating storm" and "using caution" :-D you are primed to possibly see a tornado!
It is important to know basic storm structure before attempting to chase. Many times a newer chaser/civilian will look into the core of the supercell looking for the tornado. The reason is, people immediately correlate dark skies to being the worst part of the storm. They may glance over and see sunny skies on the horizon but immediate shrug it off. It is important as a chaser to look for a rain free base on the back side of a supercell. This is your updraft region and the area that you want to look for for the development of a wall cloud (remember our discussion yesterday!) If you are on a mature supercell that has been in progress for an hour or two, odds are you will already have a wall cloud (maybe even a tornado) already evident. But to those who get on a developing supercell it is FASCINATING to observe the processes involved. Below I will attempt to walk you through the process from the birth of a supercell to tornadogenesis.
Once TCu have broken the cap and you are witnessing explosive development it is important to being to get into position to intercept.
This is about 25 minutes after the storm broke the cap and took off. Since it was immediately tornado warned you are thinking to yourself it is really show time! You get close enough to the storm and see this in the distance! TORNADO!!! .........WRONG! This is NOT a tornado or a funnel cloud or even a wall cloud! This is the storm becoming more surface based. The updraft acts as giant vacuum. It inhales warm moist air and when this air condenses clouds form. This shows the beginning stages of a wall cloud. It is fascinating to watch as little scud fragments get inhaled into this central area. Keep watching this area though, but don't be fooled by it's pointy ragged appearance.
We get a little closer and park and watch. We see the supecells core to the right and the rain free base to the left. In the center of the image we see a slight lowering to the cloud base and again more funnel looking tendrils underneath a lowered cloud base. Is this a tornado or a funnel cloud? NO! This is as I had said above, the updraft drawing in warm moist air which condenses into cloud. Again this is just the process of the evolution of a sustained wall cloud. Keep watching though!
A little further along the time line and the storm is a little closer. Notice any difference? One might say no because the scud has dissipated and now just looks like an ordinary rain free base. However it is important to notice how much LOWER the base has become as compared to when we first started. It is also VERY important to notice the feature on the right hand side. The long laminar looking cloud extending to the right or north. This is known as a beaver tail. It forms along the boundary created by the forward-flank downdraft. The area of precipitation is cool while the area you are viewing the storm from is warm and moist. The beaver tail will form where the two meet and mark it out by a long line of clouds shaped like a beavers tail. It shows that a supercell is starting to get it's act together.
We progress and the storm has moved a little bit to the north and west. An overview of events that are occurring. To the right you see the core. You also see the beaver tail demarcating the boundary. To the left you see the rain free base. But notice that pronounced lowering in the center of the image. There is your wall cloud beginning to form. At this point in time you should be able to tell if this storm is rotating or not. Watch the horizon and watch above you. You should be able to see a slow right to left motion on the horizon and left to right motion above you. A good sign if you are looking for tornadogenesis! Begin to look to the RIGHT side of the wall cloud.... The reason is you should start to see the rapid condensation of scud tags feeding into the wall cloud. This will create a tail cloud and will ALWAYS point toward the rain or core. Also note if the wall cloud has a good circulation or intense rising motions.
Notice how low the wall cloud is now. There isn't a tail cloud evident yet but notice that dark area to the left of the wall cloud. That is your RFD beginning to wrap around the area of circulation! It is time to move north before your viewing area gets cut off by the rain. An RFD wrapping around a circulation is a good sign and has been unofficially linked to tornadogenesis (more often than not). No tornado yet!
Well now we are much closer (maybe too close for newer chasers) Looking just south of due west at a VIOLENTLY rotating wall cloud. It is about to happen. Everyone knows it but are you safe? At this point in time you are in a HIGH danger area but knowing storm motion and behavior you will be able to tell if you need to get out of there or not. Right now I am at an intersection where if this were to drop a tornado and it headed due east at me I can always blast south out of harms way. But knowing the storm was moving ENE I plotted this wall cloud to pass to the west of me and into the field to the northwest of me. Once you realize you are safe, grab you tripod and camera and get ready!
The wall cloud drops a large funnel cloud with dust on the ground! TORNADO?!?!? YES! THIS is a bonafied tornado. Rapid rotation noted with tornadic winds reaching the surface. Just because there is no condensation funnel extending to the ground doesn't mean there isn't a tornado in progress. But if you want that fully condensed tornado... continue to watch the tornado as all tornadoes go through numerous evolutions.
The tornado has now fully condensed and moved safely into the field to your north west! Celebrate your accomplishment! But beware of the beast that is wrapping around the circulation! (RFD)
Now that we have covered how to successfully seek out a tornado, now it is time to post some examples of look-a-likes and why they are NOT tornadoes.
Tornado? Funnel Cloud? Nope! This was shot looking to the NW as the south end of a line of low topped thunderstorms moved by. This was on the leading edge of the line and had the look of a large white cone funnel but looking at the flag you see that the wind is gusting out of the west. This denotes outflow winds and thus ends any chance of a tornado.
Tornado? Nope! This is a the backside of a thunderstorm and what you see is a hail shaft being illuminated by the sun.
Tornado or no? Yes and No! The feature on the left is the dying La Grange, WY tornado. The feature on the right LOOKS like a large wedge but in fact it was just a large wall cloud. We were over 15 miles away from this tornado so from that distance it looks like a giant wedge.
Just busted out the back side of a low topped supercell. Look to the right and see a beautiful rope tornado out of the backside of the rain shield! Only problem is IT IS NOT A TORNADO! Remember Mother Nature is trying to fool you every chance she gets you have to outsmart her and study her and sometimes she lets you reap some benefit!
Remember.... if you aren't sure... observe. Remember what kind of storm you are chasing, remember where to be to observe a tornado, and remember if it isn't rotating then it should not be reported!!!
Thanks for reading!