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eponymous_roseThis is long overdue, and does indeed serve a purpose beyond making shiny polls (hard to take, I know). I grew up in a family that watched the weather with rapt attention, mostly because my parents both happened to be living in Edmonton (and my mom happened to be toddling around outdoors, pregnant with me) when an F4 tornado ripped through the east side of the city. As a result, understanding the various risks of summer severe weather has never been much of an issue for me (especially not now that I study it for a living) - but now that there's a whole new generation of Albertans without any personal tornado history (although Pine Lake is still fresh in many people's minds), it's becoming apparent that safety awareness has fallen a few rungs on the ladder.
There aren't right answers to all of the below questions - I encourage you to answer before viewing my takes on them beneath the cut. I've turned off result-viewing, so nobody will know if you pick something that's a bit on the iffy side. These questions have been selected because they generally demonstrate popular knowledge - both myth and fact. I'd love to get a bit more information about this, and please read the section under the cut, if only to check your score. ;)
[Poll #1152652]
(Long poll is long. My apologies to your flist - let me know if you'd rather I cut it.)
Question 1: Driving in cars during tornadoes.
Best option: Theoretically, getting out of your car and lying flat in the ditch is your best option - the immediate danger due to a tornado involves flying debris and hail, and making yourself less of a target is infinitely desirable. The exception, of course, would be in a case where you expect flash flooding, at which point seeking slightly higher ground away from the highway would be a smarter choice. Also, if lightning seems to be particularly prevalent, and you're in immediate danger of being struck, remaining in the car is safest.
There's a follow-up question: why is a car the safest place to be in a thunderstorm? It's not because of the rubber tires, actually - it's because of the metal frame of the car, which provides you with a sort of Faraday cage (there's a theorem in electromagnetism that goes like this: the electric charge in a spherical shell will be located only along the outside). If a power line were to fall on your car, you would be best to keep inside until emergency personnel arrived. Uh. Unless, I guess, your car were on fire. Then you might want to jump out. Jump.
The moral of the story? Do not under any circumstances hide under an overpass - a certain camera crew once took refuge in one during a tornado and left their camera on: due to particularly lucky wind directions, they didn't get sucked right out in the wind tunnel that would form under any other circumstances, and so went on to propagate the myth that it's safest to do that sort of thing. No. Don't. No cookie. Bad.
Question 2: Watches and warnings.
Only option: Only option, as far as I can tell - a storm/flood/tornado/whatever watch means that you should be on the lookout for averse weather conditions and listen for updated watches and possible warnings. Tie things down outside. Or, um, don't, if it's a flood. When you get a warning, it means that there is immediate danger, and that persons in or near the areas affected should prepare for the event in question.
Case in point: tornado watch means that funnel clouds have been sighted in the region. You can get cold-core funnel clouds that will rarely if ever touch the ground, at which point a watch will be issued just in case. Tornado warnings usually come too late (see below for the typical lifespan of a tornado and you'll see why) - they mean that a tornado has touched the ground in or near your area.
Warnings and watches typically lead to much frustration among the general public. Think of it this way - you live in a massive city with a population over a million. A tornado warning is issued for your city - and sure enough, a tornado rips through a couple of neighbourhoods. Evidently the people in those neighbourhoods were grateful for the warning, but 99% of the population is frustrated over the false alarm to them. This sort of thing happened after the Edmonton tornado and was one of the subjects of the subsequent Hage report on public awareness.
Question 3: Clockwise or anticlockwise?
Only option: Either. It doesn't matter where you are in the world; the water going down the drain is determined uniquely by any flaws or imperfections in the drain itself. This is just a common misconception (The Simpsons and The X-Files got it wrong!), so I thought I may as well make my case here. ;)
Clockwise and anticlockwise rotation of moving objects on or above the Earth's surface arises due to the rotation of the Earth itself, in an apparent force called the Coriolis force. (It's the same effect you get when waging war - you have to aim your missiles a bit to the right or the left to take this into account. In a more familiar example, take a stool and spin the seat, then try to draw a straight line across it - when you stop it to take a look, it'll be curved. That's the Coriolis force of the stool messing with your inertial reference frame, and it's an example of why the physics of the atmosphere is so very bizarre and counterintuitive.)
Obviously, though, this doesn't apply at all scales of motion. When you throw a ball to/at your little brother, you don't think "I should aim a bit to the left to compensate" - that's because the timescale at which the Earth is turning is so massive in comparison. Consider the time it takes the Earth to make a complete rotation (2 pi radians, for those of you who remember your geometry) - that's a day, yes? 24 hours times 60 minutes to an hour times 60 seconds to a minute gives 86,400 seconds. Thus, the Earth travels 2 pi radians every 86,400 seconds - that's the Earth rotation rate. The Coriolis frequency/parameter is defined as two times that rotation rate, times the sine of the latitude in question - take 50 degrees latitude, and you get a Coriolis frequency of 1.11E-4, which is a very small number. The inverse of the frequency gives the period, which is 8975 seconds, give or take.
The upshot of all that is you have to have something that takes about 8975 seconds to complete a rotation - about two and a half hours - for the Coriolis force to have an appreciable effect on it. Giant weather systems and hurricanes have this timescale. Water swirling round the drain does not. End of story.
EDIT: For the record, even if a sink were at the proper timescale, the water would rotate anti-clockwise in the Northern Hemisphere.
Question 4: Does a hurricane or a tornado have higher winds?
Best option: Tornadoes generally have much higher winds than hurricanes, statistically speaking. Of course, hurricanes last for weeks, whereas tornadoes...
Question 5: Lolsegue - how long does a tornado usually last?
Only option: Fifteen minutes. This is why people need to take watches seriously - warnings are nearly always too late. Of course, there are exceptions - the Edmonton tornado lasted over an hour, and the Tri-State tornado had more than enough time to cross into the eponymous (ooh, never get to use that word) three States. Generally, though, they're short-lived. Of course, they can dissipate and come back in force, or you can have several tornadoes at a time. Wait until the storm is well away from you before leaving your shelter (or ditch).
Question 6: What is this theoretical maximum for forecasting, beyond which the media is bullshitting me?
Only option: Eleven days. Yes, all those "two-week outlooks" are being a wee bit optimistic when it comes to stuff like Chaos Theory - all numerical weather prediction models forget their initial conditions beyond a certain point and take on a life of their own that has nothing to do with the physical world. That point's less than two weeks, anyway, though people are getting more and more clever about circumventing that sort of thing.
(Long-term climate prediction models, on the other hand, are seen as a boundary-value problem - describe all the conditions and constraints instead of the initialisation. Not good for fine-tuning things, but all right for general overviews.)
Question 7: Weather information sources.
Any option: It's good to stay informed about weather, but it's important to keep in mind that many local stations and commercial weather channels will just crib bits and pieces from official sources (generalisation, yes, but largely weatherpeople on the news are chosen for personality, not a degree in atmospheric dynamics). Government websites, in Canada and the States, at least, are the ones you should be consulting - they've got the money and the world's most powerful supercomputers on the job. If you trust one thing about your government, trust that.
(Of course, due to the understaffed nature of any weather station ever, if you know what you're doing enough to focus on your city alone, you'll probably get a more accurate forecast. They deal in generalisations, and considering that most areas of precipitation are only a kilometre or two across, your rainy day might just get averaged out of the equation. The industry's facing a staffing shortage, too. Lovely.)
Question 8: How tall is a thunderstorm cloud?
ONLY ANSWER: The one about the ticky box. Come on, you guys?
(Might also have accepted 10 km. That's weird, isn't it? A thunderstorm cloud is taller than Mount Everest. Weird and awesome.)
Anyway, hope that was in some way helpful. Spread the word. I'd love to discuss any of this/your severe weather experiences/negative experiences with forecasters (or positive - a girl can dream!). It's what I do for a living, after all. ;)
Thanks muchly!
There aren't right answers to all of the below questions - I encourage you to answer before viewing my takes on them beneath the cut. I've turned off result-viewing, so nobody will know if you pick something that's a bit on the iffy side. These questions have been selected because they generally demonstrate popular knowledge - both myth and fact. I'd love to get a bit more information about this, and please read the section under the cut, if only to check your score. ;)
[Poll #1152652]
(Long poll is long. My apologies to your flist - let me know if you'd rather I cut it.)
Question 1: Driving in cars during tornadoes.
Best option: Theoretically, getting out of your car and lying flat in the ditch is your best option - the immediate danger due to a tornado involves flying debris and hail, and making yourself less of a target is infinitely desirable. The exception, of course, would be in a case where you expect flash flooding, at which point seeking slightly higher ground away from the highway would be a smarter choice. Also, if lightning seems to be particularly prevalent, and you're in immediate danger of being struck, remaining in the car is safest.
There's a follow-up question: why is a car the safest place to be in a thunderstorm? It's not because of the rubber tires, actually - it's because of the metal frame of the car, which provides you with a sort of Faraday cage (there's a theorem in electromagnetism that goes like this: the electric charge in a spherical shell will be located only along the outside). If a power line were to fall on your car, you would be best to keep inside until emergency personnel arrived. Uh. Unless, I guess, your car were on fire. Then you might want to jump out. Jump.
The moral of the story? Do not under any circumstances hide under an overpass - a certain camera crew once took refuge in one during a tornado and left their camera on: due to particularly lucky wind directions, they didn't get sucked right out in the wind tunnel that would form under any other circumstances, and so went on to propagate the myth that it's safest to do that sort of thing. No. Don't. No cookie. Bad.
Question 2: Watches and warnings.
Only option: Only option, as far as I can tell - a storm/flood/tornado/whatever watch means that you should be on the lookout for averse weather conditions and listen for updated watches and possible warnings. Tie things down outside. Or, um, don't, if it's a flood. When you get a warning, it means that there is immediate danger, and that persons in or near the areas affected should prepare for the event in question.
Case in point: tornado watch means that funnel clouds have been sighted in the region. You can get cold-core funnel clouds that will rarely if ever touch the ground, at which point a watch will be issued just in case. Tornado warnings usually come too late (see below for the typical lifespan of a tornado and you'll see why) - they mean that a tornado has touched the ground in or near your area.
Warnings and watches typically lead to much frustration among the general public. Think of it this way - you live in a massive city with a population over a million. A tornado warning is issued for your city - and sure enough, a tornado rips through a couple of neighbourhoods. Evidently the people in those neighbourhoods were grateful for the warning, but 99% of the population is frustrated over the false alarm to them. This sort of thing happened after the Edmonton tornado and was one of the subjects of the subsequent Hage report on public awareness.
Question 3: Clockwise or anticlockwise?
Only option: Either. It doesn't matter where you are in the world; the water going down the drain is determined uniquely by any flaws or imperfections in the drain itself. This is just a common misconception (The Simpsons and The X-Files got it wrong!), so I thought I may as well make my case here. ;)
Clockwise and anticlockwise rotation of moving objects on or above the Earth's surface arises due to the rotation of the Earth itself, in an apparent force called the Coriolis force. (It's the same effect you get when waging war - you have to aim your missiles a bit to the right or the left to take this into account. In a more familiar example, take a stool and spin the seat, then try to draw a straight line across it - when you stop it to take a look, it'll be curved. That's the Coriolis force of the stool messing with your inertial reference frame, and it's an example of why the physics of the atmosphere is so very bizarre and counterintuitive.)
Obviously, though, this doesn't apply at all scales of motion. When you throw a ball to/at your little brother, you don't think "I should aim a bit to the left to compensate" - that's because the timescale at which the Earth is turning is so massive in comparison. Consider the time it takes the Earth to make a complete rotation (2 pi radians, for those of you who remember your geometry) - that's a day, yes? 24 hours times 60 minutes to an hour times 60 seconds to a minute gives 86,400 seconds. Thus, the Earth travels 2 pi radians every 86,400 seconds - that's the Earth rotation rate. The Coriolis frequency/parameter is defined as two times that rotation rate, times the sine of the latitude in question - take 50 degrees latitude, and you get a Coriolis frequency of 1.11E-4, which is a very small number. The inverse of the frequency gives the period, which is 8975 seconds, give or take.
The upshot of all that is you have to have something that takes about 8975 seconds to complete a rotation - about two and a half hours - for the Coriolis force to have an appreciable effect on it. Giant weather systems and hurricanes have this timescale. Water swirling round the drain does not. End of story.
EDIT: For the record, even if a sink were at the proper timescale, the water would rotate anti-clockwise in the Northern Hemisphere.
Question 4: Does a hurricane or a tornado have higher winds?
Best option: Tornadoes generally have much higher winds than hurricanes, statistically speaking. Of course, hurricanes last for weeks, whereas tornadoes...
Question 5: Lolsegue - how long does a tornado usually last?
Only option: Fifteen minutes. This is why people need to take watches seriously - warnings are nearly always too late. Of course, there are exceptions - the Edmonton tornado lasted over an hour, and the Tri-State tornado had more than enough time to cross into the eponymous (ooh, never get to use that word) three States. Generally, though, they're short-lived. Of course, they can dissipate and come back in force, or you can have several tornadoes at a time. Wait until the storm is well away from you before leaving your shelter (or ditch).
Question 6: What is this theoretical maximum for forecasting, beyond which the media is bullshitting me?
Only option: Eleven days. Yes, all those "two-week outlooks" are being a wee bit optimistic when it comes to stuff like Chaos Theory - all numerical weather prediction models forget their initial conditions beyond a certain point and take on a life of their own that has nothing to do with the physical world. That point's less than two weeks, anyway, though people are getting more and more clever about circumventing that sort of thing.
(Long-term climate prediction models, on the other hand, are seen as a boundary-value problem - describe all the conditions and constraints instead of the initialisation. Not good for fine-tuning things, but all right for general overviews.)
Question 7: Weather information sources.
Any option: It's good to stay informed about weather, but it's important to keep in mind that many local stations and commercial weather channels will just crib bits and pieces from official sources (generalisation, yes, but largely weatherpeople on the news are chosen for personality, not a degree in atmospheric dynamics). Government websites, in Canada and the States, at least, are the ones you should be consulting - they've got the money and the world's most powerful supercomputers on the job. If you trust one thing about your government, trust that.
(Of course, due to the understaffed nature of any weather station ever, if you know what you're doing enough to focus on your city alone, you'll probably get a more accurate forecast. They deal in generalisations, and considering that most areas of precipitation are only a kilometre or two across, your rainy day might just get averaged out of the equation. The industry's facing a staffing shortage, too. Lovely.)
Question 8: How tall is a thunderstorm cloud?
ONLY ANSWER: The one about the ticky box. Come on, you guys?
(Might also have accepted 10 km. That's weird, isn't it? A thunderstorm cloud is taller than Mount Everest. Weird and awesome.)
Anyway, hope that was in some way helpful. Spread the word. I'd love to discuss any of this/your severe weather experiences/negative experiences with forecasters (or positive - a girl can dream!). It's what I do for a living, after all. ;)
Thanks muchly!
no subject
Date: 2008-03-12 10:14 am (UTC)Mind you, I've seen them get the present weather wrong, so I take all future predictions with a pinch of salt. (There's also a famous occasion that I'm too young to remember where they failed to predict a hurricane).
no subject
Date: 2008-03-12 10:45 pm (UTC)I wouldn't think speed is an issue when forecasting rain, though - especially near large bodies of water, you're not going to see storms move in: they'll develop right overhead. Which is, of course, even trickier; most numerical models don't have enough degrees of freedom to account for all the possible latent heat fluxes in that sort of equation. Silly water.
Whenever I see present weather being wrong, it's usually because I'm using a dodgy source (38C and sunny! Yes, I can tell by the snow on the ground.). A good rule of thumb: if the website in question ever forecasts less than 30% or more than 70% chance of rain, it's probably not the sort of thing you'll want to rely on. Well. Unless they've found a more accurate prediction model that I don't know about yet. Which is very possible, actually.
no subject
Date: 2008-03-13 09:40 am (UTC)The speed refers to fronts, I think. They always show them and bands of rain out in the Atlantic and it's all a question of how long they take to hit various parts of the country and how much rain will be left by the time they do. Which is why the weather forecast often tells us it'll be 'showers and sunny intervals' - which is a codeword for 'we don't know'. Not that long ago when there was snow forecast in the North, one of the forecasts I looked at said every part of the country had a chance of snow. Nothing like hedging their bets.
The present weather being wrong I've usually seen on TV. The only forecasting websites I usually go to are the BBC and Met Office - any more than a couple and you get more than a couple of different forecasts :)
The most reliable way of forecasting weather: if you're going out and don't want it to rain, take an umbrella. If you do want it to rain, hang your washing out. It works more often than not.