Isn't there always a 50% chance of rain?

Question

Either it rains or it dosen't, that's 50/50. So why do I see weather reports that state 30,40,60,80% chance?

Answer 1

No.
is not always 50% chance.

Answer 2

Heh heh. Seems like it should make sense.

It's not quite that simple though. Meteorology is an inexact science, and exact conditions over a specific area cannot be predicted with 100% accuracy during a given period.

I'm sure you've experienced days that are heavily overcast, when rain seemed inevitable (therefore almost 100% chance of rain)... yet it stayed dry.

Weather patterns can change in response to "Chaos Theory", and the following analogy has been drawn:

- If a butterfly flutters it's wings in Japan today, it could lead to a hurricane in the USA next week (this is not a word-for-word quote).

Basically, what it means is that a tiny little movement of air on the other side of the globe could either become a huge storm, or never be noticed at all.

Answer 3

Only Megan got it right!
None of the rest of them understand the difference between chance, odds and probability!

If there are two ways an event can happen then it is a 1/2 chance.(0r 50%) 50% chance it will rain 50 % chance it will not. (% should not really be used here, a ratio is the right form of expression)
If their are three ways it can be decided then it is 1/3 chance. The Probability is a very different calculation. It counts all sorts of factors together to give you the probability that it will happen one way over the other.

There is a similar misunderstanding with the *Idea* people have of percentage.
Percentage can never exceed unity.
I00 doctors recommending suppository X are all the doctors out of every 100 doctors who can recommend a suppository.
You can never have 110% of anything.

It is a classic Popular Misconception.

Oops, I think Teia got it too.

Answer 4

No,

If there was an equal chance of it raining or not then you statement would be true, but with the wind flow and the seasonal changes the weather changes as well.

For example in the US if the Jet Stream drops South, as it often does for no easily explained reason, then it brings cold air South. When the cold air hits the warm humid air then often rain is the result. Colder air can support less water vapor so if you cool the warm humid air then it will have to rain to get rid of the water vapor that it can on longer support.

The Le Nenio and La Nena effects are caused by warm and cold-water circulation patterns in the ocean. The exact cause of these currents are unknown, but it is known that when those currents start to flow California will get some wild weather. As cold water flows north to California then it warms up, which changes how much water is evaporated. These changes also warm and cool the air above which changes the wind currents, which has effects that reach east across the US.

Then there is geography that has its own effect. When water-laden air hits the Rocky Mountains it can't pass the Mountain Range unless it loses some weight, the only way it can lose this weight is through rain. So the eastern side of the Rocky Mountains gets rained on and when the air finally passes over the range then it is dry. When the air currents reverse then the same happens on the different side. The deserts on the eastern side of the Rocky Mountains tells us that the air that reaches that point has been emptied of its rain.

Then their are man-made and natural affects that change the atmosphere. Forest Fires create their own weather. As the fire burns it blows tons of ash into the air, but it is all dry. When there are large amounts of fine dust clouds form. As these hot clouds hit other cooler clouds on the edge of the fire it can force it to rain before it those moisture laden clouds can reach the fire. Worse yet the clashing of the hot and cooler clouds can excite the atmosphere, and build up an electrical charge with lightning as its result. It is a common event for a dry lightning storm to generate new fires on the edges of a major forest fire.

Cities create hot spots, these hot spots can change wind patterns which changes where the rain will fall. It also allows the air over the city to hold more water, making it more humid, and less likely to rain. But, if a cold wind hits that air then it will rain.

Weather is very complex, and man has only recently begun to understand some of the causes of it. Tropical Storms and Hurricanes that hit the Gulf of New Mexico and the US get their start with warm air currents over the Sahara Desert. These warm cells of air flow west and hit the humid waters of the Gulf, which generates a lot of clouds, which due to the warmth reach high. As these clouds form then can start to rotate (due in part to the rotation of the earth). Rotating clouds become storms, which can turn into Tropical Storms, which can then turn into Hurricanes.

Weather is random like a coin toss it depends on effects from all around the globe. Some of these effects are as minor as a dust storm in the desert, or as strong as a sudden change in the Jet Stream. Chaos theory states that something as minor as the flap of a butterflies wings can start a change of circumstances that can result in a change in the weather thousands of miles away; thus the name “The Butterfly Effect.”

Chance does have a lot to do with the weather, but it is chance determined by climate, geography, wind conditions, the solar wind, hot and cold sources on the earth and in the water, and a lot of effects that I haven’t named, some of which we don’t even know. This is why there is only a chance of showers and a likely hood of some weather event happening. This is why the path of a Tropical Storm or a Hurricane can’t be accurately determined; some storms have even gone back on themselves and done loops in the ocean. When I was young weathermen only dared to predict the weather for three days, after that it was a guess. Now weathermen dare to predict the weather for an entire week, but still sometimes they are wrong and the farther out the forecast is the more chance for an error.

Answer 5

Because 100 % of the time there is merely a chance of something happening. Rain included. The weather is based on beautiful days being the norm (0%) so if tomorrow there will be some cloud accumulation but not alot. The weather service puts a small percentage (10%) on the chance of rain. i hope this answers your question.

Answer 6

The way I understand it, a 50% chance of rain equals to the amount of coverage of the rain over a specific area, meaning that about half the people in that given area will see rain. The chances of rain go up or down according to the atmospheric conditions; the percentage of rain depends on how favorable those conditions are to be conducive for rain.

For example, I live in the Dallas/Fort Worth area. Dallas and Fort Worth are both major metropolitan cities, but they are nearly 40 miles apart. When they do weather forecasts here and they put us under a 50% chance of rain, that means 50% of the immediate DFW area will see rain.

Answer 7

No, there's not always a 50/50 chance. Tv stations report the rain chances based upon their viewing area. If they feel like 20% of the viewing area will get rain, then it is a 20% chance. It depends on the size of their coverage area the rain will pass over.

Answer 8

The percent chance is all based on a number of different meteorological factors. Technically yes, you're right, but the percentage is based on the chance it will rain based on the situation. If there's high pressure, you're in the middle of a drought and it's cold outside, it's pretty safe to say there's a 0% chance of rain. But if a ton of data says rain and a few things say no rain, it's more of a shade of grey. You can't just ignore the stuff that says yes, and you can't ignore the stuff that says no (unless it's way out to lunch). It's a dumb system, and I think it should be yes it will or no it wont. That's how I forecast, and sometimes it bites me and sometimes it doesn't.

Answer 9

i just took this in a statistics lesson a few weeks ago. now you would normally think that it either rains or it doesnt but then you're leaving out many factors such as high/low pressure, time of the year and many other factors that affect the probability of rain. Plus, rain is not the best example because some of the statistical analyses done to figure out the probability of rain is actually based on guessing the direction of a certain storm or even cloud clusters...

Answer 10

Your premise is wrong. Unless it rains on 50% of days of the year, the probability of rain is not 50% but a lot less than that. If it rains, on average, one day in four then the probability is not "Either it rains or it doesn't that's 50/50" but "Either it rains or it doesn't or it doesn't or it doesn't that's 25/75".

Answer 11

The nationwide climate service defines the prospect of precipitation this manner: over the years, the NWS has recorded climate archives and prerequisites, as well as logs of no matter if there became a measurable volume of precipitation (.01 inches or extra) hence. They then evaluate the present circumstances with similar historic circumstances and observe what number cases it ended up easily raining. So, in the adventure that they look into 100 archives and it rained 60 cases out of 100 with similar circumstances, then they anticipate a 60/100 or 60% chance of precipitation. lately, they use very complicated computing gadget modeling to foretell the prospect of precipitation, the position the computing gadget simulates what it thinks the elements will be in accordance to modern and envisioned circumstances. It then runs this methodology persistently many cases till they get a consensus between the fashions as to what the envisioned danger of precipitation will be.