What makes the sky turn green before some tornadoes?
455657
I have been told it is hail and the sunlight is refracted from  it and thats why it looks green.  The brighter the green the more hail is in the sky
318117
For the same reason the sky looks blue. If the air were perfectly transparent and without dust or water vapor etc, you would see the distant greeny hill look green(y).\n\nBut due to the presence of microscopic dust in the air, the distant objects take on a very slightly bluish hue.
408414
The easy answer is, of course, from the potato salad and burrito you had earlier. A more dignified answer is at Scientific American. \n\nSimply put, wind is the motion of air molecules. Two concepts are central to understanding what causes wind: air and air pressure. Air comprises molecules of nitrogen (about 78 percent by volume), oxygen (about 21 percent by volume), water vapor (between 1 and 4 percent by volume near the surface of the earth) and other trace elements. Every time we breathe, the air we inhale is composed of about the same relative ratios of these molecules, and a cubic inch of air at ground level contains about 1020 molecules. \n\nAll of these air molecules are moving about very quickly, colliding readily with each other and any objects at ground level. Air pressure is defined as the amount of force that these molecules impart on a given area. In general, the more air molecules present, the greater the air pressure. Wind, in turn, is driven by what is called the pressure gradient force. Changes in air pressure over a specified horizontal distance cause air molecules from the region of relatively high air pressure to rush toward the area of low pressure. Such horizontal pressure differences of all scales generate the wind we experience. \n\nThe areas of high and low pressure displayed on a weather map in large part drive the (usually) gentle ambient wind flow we experience on a given day. The pressure differences behind this wind are only about 1 percent of the total atmospheric pressure, and these changes occur over the range of multiple states. The winds in severe storms, in contrast, are a result of much larger and more concentrated areas of horizontal pressure change. Tornadoes are great examples. In June 2003 Tim Samaras of Applied Research Associates placed a scientific probe in the direct path of an F4 (devastating) tornado near Manchester, S. Dak. He found that the air pressure dropped by 10 percent of the total atmospheric value over the radius of the tornado. The magnitude of this air pressure change, and the very short distance over which it occurred, explains why the winds are so destructive in this phenomenon: air molecules are very quickly accelerated into the very low pressure at the center of the tornado where the water vapor contained in the air often condenses, creating the often visible "condensation funnel."
804432
The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. \n\nHowever, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. \nOn Earth, the sun appears yellow. If you were out in space, or on the moon, the sun would look white. In space, there is no atmosphere to scatter the sun's light. On Earth, some of the shorter wavelength light (the blues and violets) are removed from the direct rays of the sun by scattering. The remaining colors together appear yellow. \n\nAs the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes.
543373
We have air around us. The atmosphere has high preasure and low preasure. When the high preasure area turns into low preasure, the air moves from high preasure area towards the low preasure. This movement of air from one area to another causes the wind. \n\nIt has nothing to do with clouds. The faster the low preasure area is formed, depends on whether you have clouds, or thunderstorms. Low preasure areas causes rain. This is why normally you have winds before the rain.
666982
Actually a storm came through Fort Worth in about 1995, the sky was about as green as a lilly pad.  We didn't get the severe weather where I lived, but FW got grapefruit sized hail in the park that actually killed several people.  Now that I study and work in weather I know what causes the green discoloration when the light refracts off hailstone in the air it causes a light green light, with more widespread and intense hail you get the darker green
1005699
The same thing that causes prizms in crystals.  It is the colors of light, the rain condenses them just as the crystal does
481590
Tornadoes are created from severe Thunderstorms. They occur when a high pressure front meets head on with a low pressure front. No where is this more evident than in our mid-west, otherwise known as tornado alley, from the Canadian provinces to the Gulf of Mexico. Here, the Siberian express from Canada meets the warm tropical front from the Gulf of Mexico.
82863
The problem is, the air refracts the light as the sun rises. When you see the sun as it rises, it is still actually below the horizon, and it is just that the layers of air are bending the light down so you can see it. The color that gets bent (refracted) the most is the violet light, then the blue, then the green and so on. That is what is responsible for the green flash (since your eye is not as sensitive to the blue and the violet colors, it sees green first). The red actually arrives last, because of these refraction effects. \n\nThe speed of light difference between red and violet is extremely small in air, so this should not have a large influence in the timing, particularly when the atmosphere is only a few tens of miles thick at most (99% of the atmosphere is in the lowest 30 Km).\n\nAfter thinking about this a minute, I realized that you are asking because the sun looks red when it first comes up. This is NOT because the red gets here first. The blue wavelengths are scattered away from the almost white sunlight by the nitrogen and oxygen in the air, leaving the red color. As the sun rises, it goes through less air, and less blue is scattered away, and the sun becomes orange. As the sun rises even higher in the sky, less blue is removed, so the sun looks yellow.
105363
For a tornatdo to form, there must be cold air, warm air, horizontally spiraling air (casued by the coriolis effect), flat land, no water present. There must be an oncoming wind, and cold and warm aiar that is colliding from the northern and souther latitudes. When the masses of air meet, the warm or moist air will rise, since its density is lower than cold or dry air, ando this will create an upward motion. Now, the oncoming wind will come along (it will be spiraling already), and when it makes contact with the area in which the air masses met, the spiraling wind will basically be violently set upright and so a tornado will form. In the northern hemisphere, the winds will go in a counterclockwise direction and in an inward spiral. (This will be partailly due to the Coriolis effect& if you're in the southern hemisphere, the winds will go in a clockise direction). This is the basic science of tornadoes, as i have just learned this year in my Earth Science course.
124314
Actually, this happens only under certain atmospheric conditions, when the air is quite clear. It is because the speed of light in the layers of air near the ground is slower than the speed of light in layers of air above that. Therefore, just like a lens, the light is bent by this gradient in the speed of light. \n\nRefraction of light is a wavelength-dependent phenomenon. The longest wavelengths are bent, or refracted the least. and the shortest wavelengths are bent the most. The reds, yellows and oranges are the long wavelengths, and they will bend the least, and will head off into space. The shorter wavelengths, the blues and greens and violets will be bent down by the atmosphere to be visible at the ground. In fact, the sun is actually below the horizon for the last few minutes of the sunset. The light has to bend around the earth, and the color that gets bent the most includes the short wavelengths. \n\nWhy do we see green in the green flash, and not violet or blue? There is also Rayleigh-Tyndall scattering going on, caused by the small nitrogen and oxygen molecules in the air. The shortest wavelengths are most scattered by the air molecules, and are scattered out of the sunlight, leaving longer wavelengths for us to see. The blues and violets have very short wavelengths, and are therefore scattered the most. (This is the same process that creates blue skies and orange and red suns at sunset). However, in this case, the yellows and reds and oranges are not present in the sunlight as the sun sets below the horizon, but have travelled out into space, so only the greens, blues and violets remain. The blues and violets are scattered away, leaving the green for us to see as a green flash. \n\nA more complete explanation complete with pictures is in the references.\n\nIt is also interesting to note that the moon can also exhibit a green flash, or a green edge (and also a red edge, in a kind of red flash). At the poles, when the sun is barely below the horizon for hours, the green flash can last for hours apparently, according to friends that have seen it.
312470
The colored boxes on weather maps indicate areas under severe thunderstorm (yellow) or tornado (red) watches.  They are used to show areas that may see severe thunderstorms and tornadoes.
163797
In the midwest, the mountains to the west and the Gulf of Mexico to the south produce the layers of cool, dry air and warm, moist air, these coditions are favorable for tornado formation. These conditions happen much less often toward the coasts. Tornados aren't uncommon on the east coast though. In fact, areas hit hard with hurricanes(Gulf Coast) have tornado outbreaks too because the hurricanes produce apt conditions for formation.
499353
The first thing that has to happen is that you have to have two different patches of air moving toward each other from opposite directions, with a warm one on the bottom and a cool one on the top. \n\nThe next thing that happens is that the warm air rises. After the warm air goes up, the cool air comes down to take its place. So now the warm and cool patches of air are moving side to side and up and down. So they make a spinning patch of air along the ground.\n\nUsually when a tornado is starting, it happens during a storm. So there's lots of air moving around already. If a draft of air from the storm comes along close to the ground and then moves upwards (called an "up-draft"), it will pull the spinning air upwards.  Then comes the part that scientists don't understand quite as well. So far the spinning air is still really really wide. Somehow it gets pulled in really tight so that it makes a tornado.
234935
Short answer, they are called "tornado;" as you will see below, tornadoes usually rotate in a counter-clockwise direction in the northern hemisphere, clockwise in the southern.  In the rare event of it spinning in the opposite direction, which I believe was the nature of your question, it is called an "anticyclonic tornado."\n\nTornadoes normally rotate in a cyclonic (counterclockwise) direction in the northern hemisphere, as the warm air in which thunderstorms usually form sweeps north and jet streams come from the west, creating a situation in which the storms rotate. In the northern hemisphere, this rotation is counterclockwise, and in the southern hemisphere, clockwise. The tornadoes usually rotate the same way. Sometimes opposite direction swirls develop under a thunderstorm. About 1 in 100 tornadoes in the northern hemisphere rotate in an anticyclonic direction.\n\nI hope this helps.
55008
Thats a simple science question.\nRainbows almost always appear during or right after a rainstorm. The water vapor in the air forms to act as a prism. With the right angles of sunlight in relation to the water vapor, the "prism" breaks the "white" or "ultraviolet" light up into it's true colors which are red, orange, yellow, blue violet and green. I always use to remember the primary colors by using the accronym, "roybug" changing the "u" to a "v" for the violet.
486406
The Weather Ball changes color based on the weather forecast:\n\nWeather ball red, warmer weather ahead\n\nWeather ball blue, colder weather in view\n\nWeather ball green, no change foreseen\n\nColors blinking bright, rain or snow in sight.\n\nSee the following link for the weather ball's history. It used to be located downtown and could be seen for many miles around.