How does a tornado form:
In a regular garden variety thunderstorm warm moist air shoots upward meeting colder, dryer air. Because the warm moist air is lighter than the cold dry air it will form a strong updraft within the thunderstorm. During the storm, the cold air and warm air combine in a set pattern: the cold air drops as the warm air rises. As the warm moist air rises, it may meet varying wind directions at different altitudes (wind shear). The wind shear creates an invisible horizontal spinning effect in the lower atmosphere. Now because we have warm moist air in the updraft, it hits this horizontal tube of spinning air and tilts it into a vertical position. As the updraft tightens the spin and it speeds up (much like a when an ice skater pulls in their arms and spins faster. The warm air eventually twists into a spiral and forms the funnel cloud that we all associate with a tornado.
There are two types of tornadoes: those that develop out of a supercell thunderstorm and those that form out of a regular thunderstorm.
Tornadoes that form from a supercell thunderstorm are the most common, and often the most dangerous. In the blog post "Types of Thunderstorms" I talked about Supercells and a little about the tornadoes they form. This kind of tornado has a life cycle. First, the mesocyclone , along with the rear flank downdraft( RFD), starts moving towards the ground. At this time a small funnel appears to build up at the base of the wall cloud. Once the RFD reaches the ground, the surrounding dirt rises up, causing damage to objects on the ground. The funnel touches the ground immediately after the RFD, forming a tornado.
The next stage starts when the RFD, begins to cool. The distance the tornado covers, depends on the rate at which the RFD cools. The long lived tornadoes during the Super Dixie Outbreak were a good example of what happens when there is plenty of warm moist air for the tornado to feed on. Once the RFD cannot provide any more warm air to the tornado, it begins to die. The lack of a warm air supply causes the vortex to weaken and contract . As the tornado weakens, the mesocyclone also starts to dissipate. There is one important thing to keep in mind, a new mesocyclone can start very close to the dying one. So you don't want to let your guard down too quickly.
If you recall my discussion on weather radar, you will remember, I said doppler radar can't see wind; it can only see objects like rain, hail, or even birds. Also, doppler radar in general cannot see tornadic scale rotation, it is much too small. What we see on radar is the much larger scale rotation of the entire thunderstorm rotating. Gustnadoes and landspouts pose a very significant challenge to forecasters. not only because they can form in rather benign environments. But also, most of the time they form before precipitation is detected on radar. Another thing is most of the rotation occurs close to the ground, which is below where the radar can see.Rarely does radar give us a good view of non-supercell tornadoes. Because of this, non-supercell tornadoes are next to impossible to predict.
What does a tornado sound like:
What does a tornado look like:
Picture of an Elephant trunk tornado
There is a lot we don't completely understand about tornadoes especially near the base of the tornado. A multiple vortex tornado (sub-vortices or suction vortices) is one that has mini vortices inside the bigger main vortex. I think most toradoes have these suction vortices. Most of the time no one can see them because they are rain wrapped or hidden by debris in the funnel. I've seen a few multi vortex tornadoes. In the ones I've seen these sub-vortices formed at the base of the tornado. Inside the main vortex there are several forces at play: inflow and outflow angle, rotational motion, centrifugal forces, pressure gradient forces, and even the winds in and around the tornado vortex. I think these complex forces form relatively calm areas inside a tornado, therefore areas inside the parent tornado will be spinning faster that others. Sub-vortices can cause narrow areas of extreme damage inside the main tornado damage path. Even though a tornado can range from less than one hundred yards to over two miles in width, these smaller vortexes may only be 60 or 70 feet in diameter and follow one another, this is often referred to as training. The winds in these sub-vortexes can easily spin in excess of 150 mph and are most likely responsible for a majority of a tornadoes destruction. They are one of the reasons people think tornadoes can skip over one house and hit another house across the street.
Local outbreak: normally this is at a county or state level.
Line outbreak: in this case the tornadoes form around the same time along a line. A line outbreak can be at the state level. However, normally it encompass several states.
Progressive outbreaks: are when several tornadoes form over a 12 to 72 hour time frame. this kind of outbreak progresses toward the NE, E, or SE. A progressive outbreak is like the one we just saw in the end of April.