# Why do clouds move in a certain direction?

by GeekyChick
Tags: clouds, direction
 P: 8 I've never really studied clouds or the movements of clouds or paid any attention to the science that I was taught in school, so if this question seems stupid, I'm sorry. I always watch the clouds from my window and they always go the same way, but today they are going the opposite direction. Does this happen because of the wind or is this even possible. Like I said I never really studied or paid any attention when taught, but I'm starting to really get into clouds and want to learn more.
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 PF Gold P: 4,287 Yes, it's possible. The typical direction you see is probably representative of the "prevailing winds" in the area, but wind direction is ultimately sensitive to the context of surrounding weather patterns so it's not fixed. There are some well known prevailing winds around the world like the "trade winds"
 P: 8 So like from a normal thunderstorm to a possible tornado difference?
Mentor
P: 26,557
Why do clouds move in a certain direction?

Here is the answer.

 In general, clouds move at a speed and direction of the prevailing wind at the altitude where the clouds are occurring. The direction and speed of the wind depends on the pressure differences between the areas of high and low pressure. As you go up in altitude over a particular location, the winds will vary in direction and speed. Usually, the speeds increase with altitude up to a certain point, and then they decrease. Rivers of fast-moving air in the atmosphere are called "jet streams," and occur at altitudes from 25 to 40 thousand feet above the ground. Speeds in the jet stream can reach as high as 175 miles per hour or more. When clouds occur at that level, they move very quickly. The location and strength of the jet stream has a big effect on the weather at a particular location. At a lower level, the the windspeed may be different, and the direction may be different as well. Sometimes you can see clouds at several different levels, and they may be moving in different directions.
 P: 8 So like the difference between an extremely windy valley where the wind changes the direction all the time and an area that is rarely windy and is almost always the same?
Mentor
P: 26,557
It has to do with the altitude of the clouds. You're observations are very good.

If you live in the US, you probably have noticed that high clouds tend to move mostly in a west to east direction, with slight variations. You have also noticed that sometimes the clouds change direction, this can be caused by a number of events that effect your local weather. I just looked outside to see which directions the clouds where going right now and the skies are clear, oh well.

Your guess about windy valleys is correct.

 In areas where winds tend to be light, the sea breeze/land breeze cycle is the most important to the prevailing wind; in areas which have variable terrain, mountain and valley breezes dominate the wind pattern.
http://en.wikipedia.org/wiki/Prevailing_winds
 P: 8 Okay well its nothing but clouds here. Can you recommend any good books on cloud physics?
Mentor
P: 26,557
 Quote by GeekyChick Okay well its nothing but clouds here. Can you recommend any good books on cloud physics?
I'm afraid I wouldn't know what to recommend, sorry. But if you like clouds, take a look at this website.

http://cloudappreciationsociety.org/
 P: 8 Thank you!
 Mentor P: 15,170 "Prevailing" means just that, prevailing. The prevailing winds indicate the direction the winds blow in the lower troposphere on average. The term does not mean "all the time". The canonical joke about three statisticians who went duck hunting comes to mind. The statisticians see a duck flying across in front of them. The first statistician shoots, but his shot goes to the left of the duck by 10 meters. The second statistician shoots, but his shot goes to the right of the duck by 10 meters. The third statistician shouts "we got it!" What's happening now? Are the winds prevailing from the west? Check out this site: http://hint.fm/wind/ This site shows the surface winds at points across the US. Today, the northeastern seaboard is seeing winds from the east. Winds are strong across the plains, but are definitely not moving west to east. The winds in the plains are blowing strongly from the north in some places, strongly from the south in others. There's a line separating the northerly winds from the southerly winds. At the top and bottom of that line you'll see two nice little swirly patterns. Those are probably not nice places to be right now. Those are the surface winds. Oftentimes winds are strong when the sky is clear. So, what's today's weather look like? http://www.accuweather.com/en/us/nat...tellite?play=1 The above site cycles through the last six weather satellite photos, separated by 15 minutes. Some things to notice: - A lot of the places that have high winds have no clouds. - The clouds oftentimes aren't moving in the same direction as are the surface winds. - The clouds oftentimes aren't moving to the east, the direction in which the prevailing winds blow. Here's one last site: http://earth.nullschool.net This site shows the surface winds for the entire globe. It is so very cool. You can rotate the Earth so you can see different parts of it, zoom in, zoom out. As I said, cool. Here you can see two much worse swirly patterns, one in the Arabian Sea and the other in the Pacific off the coast of Mexico. The first is Tropical Cyclone 02A and the other, Hurricane Christina. Those definitely are not nice places to be right now. Bottom line: Prevailing doesn't mean always. It means "on average." Keep those statistician duck hunters on mind when you read about prevailing winds.
PF Gold
P: 1,356
 Quote by GeekyChick Okay well its nothing but clouds here. Can you recommend any good books on cloud physics?
Maybe not exactly "cloud physics," but a beautiful book on clouds, which will teach you a lot, is The Cloud Book: How to Understand the Skies.
 P: 14 Sometime between 1642 and his death in 1647, Evangelista Torricelli gave a lecture from which his notes survived. After he died they were among the few references to his work that remained. Upon being examined it was discovered they contained the earliest correct scientific explanation of the origins of winds. ... winds are produced by differences of air temperature, and hence density, between two regions of the earth. It is unfortunate Torricelli did not put his thoughts to paper as assiduously as his friend Galileo did, and because of this many of his contributions are unrecognized. but what is credited to him is impressive and worth a glance. http://www-history.mcs.st-andrews.ac...orricelli.html Having given credit to whom it is due, I turn to the matter at hand to speak for myself. The area near the equator receives more Sun. the air is warmed, expands and displaces cooler air elsewhere and in time cools, there. The cool air for its part is pushed, moves, finds a place in the Sun, warms in its turn and repeats the endless loop that is constantly circulating from equator to pole and back again. At the same time, the Earth turns under the wind. seeing as wind direction is reckoned with respect to the ground, the circulation takes on a clockwise character in the northern hemisphere, when viewed from above. And an anti-clockwise rotation in the southern hemisphere. All things being equal nothing is ever equal. Local variations in temperature and thus pressure with respect to other places constantly alters the general nature of the winds into the particular nature of them. Topography is also an influence. At one point wind flows this way because of that, at another point flows that way because of this. At one time winds are brisk at another gentle, on occasion things get very exciting indeed. This of course does not address the actual question. But moving to that it must be noted that warm air can hold more water than cool air and that clouds form, or dissipate, when the temperature of the air changes. As air cools, it sheds water in tiny drops. When air warms it absorbs what moisture is at hand. Thus air near the ground absorbs water and carries it aloft where the air cools and sheds the water to form clouds at the time and place the air can no longer support the water it holds. Often the air rises because it is warmer and lighter than nearby air. And often it encounters a mountain and rises because the wind forces it to climb. I hope this provides a better foundation to stand upon while considering clouds and where they come from, where they are going, and why they move as they do. Naturally, the ideas I have mentioned belong to others while the mistake I have made are my very own.
 HW Helper P: 7,134 In southern California (and other locations) the winds are affected by either high pressure zones (clockwise rotation), or low pressure zones (counter-clockwise rotation), and their location relative to where you live. For example, a high pressure zone to the north results in somewhat east to west flow. High pressure zones can also trigger a condition called Santa Ana winds. http://en.wikipedia.org/wiki/Santa_Ana_winds In addition if the prevailing winds are near zero, the air heated by the Sun tends to create a flow that moves west in the mornings and east in the evenings.
P: 8
 Quote by rcgldr In southern California (and other locations) the winds are affected by either high pressure zones (clockwise rotation), or low pressure zones (counter-clockwise rotation), and their location relative to where you live. For example, a high pressure zone to the north results in somewhat east to west flow. High pressure zones can also trigger a condition called Santa Ana winds. http://en.wikipedia.org/wiki/Santa_Ana_winds In addition if the prevailing winds are near zero, the air heated by the Sun tends to create a flow that moves west in the mornings and east in the evenings.
I was talking about a valley in California
P: 14
 Quote by GeekyChick I was talking about a valley in California
Actually, dear girl, you were talking about wanting to know more about clouds.
 P: 8 I meant when I mentioned California, but thank you for the clarification. :)
P: 412
 Quote by GeekyChick Okay well its nothing but clouds here. Can you recommend any good books on cloud physics?
I recommend the latest edition of "A Short Course in Cloud Physics" by Rogers and Yau.
P: 3
 Quote by GeekyChick Okay well its nothing but clouds here. Can you recommend any good books on cloud physics?
I would recommend Cloud Dynamics by Houze.

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