The downside of spring in the central US.

[Lessinath]

Comparing a threat that normally isn't there at all but is occasionally a very serious threat to a long term threat like cancer is very poor and very annoying logic.

For warnings? About 75% are false alarms. However, this ignores a few things:

Very weak tornadoes, or tornadoes that don't hit anything are often unreported.

I think, intentionally or not, you're combining every type of warning into tornado warnings in your mind and getting a large number, possibly over 20, per year. This is just flat out wrong. Even in the most tornado prone areas in the country, they average two tornado warnings per year for any given location. The average warning length time is 45 minutes. This means if you take tornado warnings seriously you loose 90 minutes on average of your 525949.2 minutes in a year. Hell, you probably waste more time in a year just doing literally nothing. Seems like a very good trade for being safe to me. It's hardly a massive inconvenience. Sometimes they effectively cluster, in that one year you'll have 6 or 10 and then you'll go a few years without any, but it's still at most a few hours a year. That's why it's a shoddy excuse.

Most tornadoes are weak and small - but still plenty powerful enough to at least ruin your week (and your house) if they hit you. If you're in a mobile home, your chance of injury or death in a storm greatly increases. Of those 25% that produce tornadoes, you won't hear about most of them. The media really only mentions the ones that are interesting, so this gives a false impression that tornadoes are far rarer than they are.

This and this are good reads related to the subject of false alarms. You can read them in either order, as the first is used for one of the references in the second anyways - but the second is shorter, so you may wish to read it to just get a general idea.

For tornado watches, around 60% have at least one tornado. But this is unfair because tornado watches are extremely large, often covering entire states and it ignores watches that have multiple warnings.

I'd also like to make clear the difference between a tornado watch and a tornado warning. A tornado watch means "conditions over a large area are favorable for storms that can support tornado formation." Sometimes they're a bit more urgent than that, but usually not. That means you should just continue what you're doing and just make sure to start paying attention to the weather if storms start approaching, with the exception of things like, oh, that long hike out in the woods miles from shelter - you'd want to plan it for a future date instead. A tornado warning, however, means "this storm is immediately likely to or actively producing a tornado and you need to be in a safe location if you are in its path."

A large number of false tornado warnings** are actually issued due to false reports from the untrained public who, quite frankly, don't know what they're looking at or talking about when it comes to tornadoes. Browse through the scary looking cloud club (seriously) to take a look at what I mean. How many of those look like funnel clouds/wall clouds / tornadoes to you?

**I'd have to look through individual warnings to find out exactly how many, and can't be bothered. However, the data is readily available so you're welcome to look if you want.

[geodave]

You'd think people would move out of 1/3 of the country just to be safe....

[Lessinath]

Not for something that only has a realistic shot at happening a few times a year at most.

What happened Friday was relatively rare and happens at most a few times a year. Otherwise tornadoes are very much hit-or-miss events. Interestingly, besides the tornadoes this was a major hail event too - including a 4.25 inch(!!) hailstone in Carrol, Kentucky.

[AdrenalinDragon]

What's up with Hurricanes and Tornados in America. It's always America.

Still, I'd rather live in America than England for that reason.

[Lessinath]

Oh, hurricanes happen elsewhere - you just don't hear about them. America does get the lion's share of tornadoes, however. India, Bangladesh and Argentina also get a lot and Europe has had some major tornado outbreaks.

With that said, tornadoes can happen anywhere the conditions are right, even in the middle of mountains or even the desert, but it's rare for them to be reported there when they do happen due to the very sparse population.

[CamdenT]

I remember a few years ago we had a tornado here in Connecticut and it was a really big deal. But otherwise its been pretty quiet. Except last fall when we had an awful snowstorm in October- practically the whole state had no power. I missed school for a week because our high school was being used as an emergency shelter.

[BigOto2]

Every year, around Seattle we all have the same mindset about the weather: This year is colder than most years.

While spring hasn't truly arrived yet, it hasn't really shown many signs of warming up to a comfortable level yet. I can imagine it will be the same crappy weather until June as usual, too.

[Lessinath]

Oh I'd take loads of rain and wind over the occasional tornado supercell*. Any year. Sure, they're interesting from a science POV but tornadoes suck**.

**Figuratively.

Unsolicited science warning:

[Click to Show Content]

Also, some engineering knowledge is helpful in understanding what happens here.

In a literal sense, the pressure drop (or "suction") in a tornado is insignificant compared to the wind itself just flat out blowing that hard. In an EF5 tornado the lifting force on the roof of a house, taking into account both suction and aerodynamic lift, is about 90 pounds of force per square foot - which is a lot, actually. However, the force on the walls from the wind can exceed 750 pounds per square foot. In a weaker tornado, the pressure plays an even weaker role but ALL the forces are weaker then (duh) as well. Of course, 90 pounds per square foot is more than enough to lift off your roof and have it land in the next county over.

The way a house fails is pretty straightforward, although there are a lot of variables.

Take a look at this: http://www.spc.noaa.gov/efscale/2.html (for your typical home specifically)and this: http://www.spc.noaa....o/ef-scale.html

If you're not aware, a supercell thunderstorm is a thunderstorm with a long-lived, persistently rotating updraft called a mesocyclone. They can actually be embedded in other storm types, such as squall lines or hurricanes, but are most often isolated and under otherwise clear air. If they get very intense, they can induce rotation in the atmosphere around them, causing the entire storm to rotate and possibly forming a mesoscale convective system (don't ask). The direction of rotation is usually anti-clockwise (cyclonic) in the northern hemisphere. This is actually NOT due to the Coriolis effect, but instead due to the overall wind patterns that form these storms.