Predicting tornadoes before they hit

[Laurinda van den Berg]

Yesterday afternoon two tornadoes touched down in South Africa. I have always been fascinated by tornadoes and apart from the basic signs to look out for, i.e greenish, black skies and large hail, a funnel, wall cloud, mesocyclone etc, what other cloud conditions or temperature changes can a person look out for? The SA weather service put out a warning and watch for thunderstorms and heavy rain, but since tornadoes can be unpredictable, how do most stormchasers identify situations ripe for a tornado to form?

 

[rdale]

Look at the first and third topic in this forum for more info on that...

 

[David C Watson]

Well, for my knowledge, I do not have an expertise on the climatology of South Africa but a tornado is a tornado is a tornado no matter when or where they occur. They almost always occur in supercell thunderstorms. They can also occur from non-supercell thunderstorms as well. A lot of major ingredients have to come together for there to even be a tornado to occur. Most commonly a tornado in a supercell thunderstorm will develop in the back edge of the thunderstorm known as the "rain-free" base, which is the updraft. As rain cooled air flows from the front flank of the supercell, it then gets recycled to the back edge where when the moisture reaches its dew-point temperature to form clouds that will rise back up into the updraft which forms the wall-cloud at the base of the rotating updraft. From there the cooler moist air squeezes on the updraft like as your hands would squeeze a tube of tooth paste and shoot the updraft up even faster which aids in tornado-genesis. From a storm spotters perspective the safest vantage point to view a tornado safely would to be on the southeast edge of the severe thunderstorm. This will help you have a clear vantage point from not being blinded by the sun and to avoid the large destructive hail or damaging winds that will accompany the tornadic supercell. Since most stronger supercells tend to turn right you would then have to adjust your position more south and southeasterly accordingly.

 

[Wes Carter]

I'm going to defer to some of the more experienced chasers because I don't want to confuse you with a less than ideal answer. But I think you all do face some serious challenges in forecasting tornadoes because you don't have as well developed of a weather forecasting and warning system in South Africa, but it looks like there are some efforts to remedy that. In this article it says that Doppler radars are being installed over the country to provide better warnings. The site that article is on is for storm chasing in South Africa, so you might be very familiar with that site already. I just found it in a Google search but have found it to be very informative.

By the way, the video of the Duduza tornado yesterday is VERY impressive. You cannot classify tornadoes by visual cues, but in my uneducated opinion it looks pretty violent:

 

[Wes Carter]

...Since most stronger supercells tend to turn right you would then have to adjust your position more south and southeasterly accordingly.

David, she's in South Africa which is in the Southern hemisphere. There are going to be some differences due to the warmer air being to the north rather than the south as it is here, plus the Coriolis force, difference in geography, etc...

 

[Skip Talbot]

greenish, black skies

While these colors may tip you off that there is a large storm nearby, they don't have much to do with the tornado potential but rather the way light filters through clouds and precip. Plenty of green storms don't produce tornadoes, and I've seen a variety of tornadoes that were not associated with a green core.

From a storm spotters perspective the safest vantage point to view a tornado safely would to be on the southeast edge of the severe thunderstorm. This will help you have a clear vantage point from not being blinded by the sun and to avoid the large destructive hail or damaging winds that will accompany the tornadic supercell. Since most stronger supercells tend to turn right you would then have to adjust your position more south and southeasterly accordingly.

As Wes pointed out, the Coriolis effect spins things in the opposite direction down in South Africa so the supercell structure is mirrored. So that should be:
From a storm spotters perspective the safest vantage point to view a tornado safely would to be on the northeast edge of the severe thunderstorm. ... Since most stronger supercells tend to turn right you would then have to adjust your position more north and northeasterly accordingly.

 

[Andy Jackson]

Without weather models the best environmental clues as to the tornado potential that day is:
(in my opinion)
-Hot & humid conditions
-Relatively strong surface wind throughout the day

When thunderstorms do form look for constant lightning flashes as well as an increase in winds flowing into the storm.