Putting together a weather forecast is similar to buying a jigsaw puzzle at a department store. Once you take is home, you have to figure out which piece to start with first.
Modern forecasters use radar and satellite images, current surface observations, computer model projections and their own expertise to put together the most accurate weather forecast possible.
LIMITATIONS: WHY FORECASTS CAN BE WRONG
You may wonder why a day forecast to be sunny and warm turns out to be cloudy and miserable. It may be hard to believe in this modern age, but computer models and forecasters can sometimes be wrong. The motions and interactions that go on in the earth's atmosphere and at the earth's surface are so complex that conditions can change quickly.
Let's use an everyday example to try to understand just why it is that forecasts can sometimes go wrong. What if you were playing a game of touch football in the park. The ball passed to you is thrown over your head. It lands in a nearby creek and begins to float quickly downstream.
The creek has lots of curves. There are rocks and downed branches scattered about the creek bed. What's more, the water is moving very rapidly in the middle of the creek, but much slower along its edges. Can you predict where the football will end up in five minutes?
Predicting where that football will be five minutes from now isn't easy. A lot can happen in five minutes.
For instance, the ball could get caught on a branch or be carried swiftly down the middle of the creek with no interruptions at all. Perhaps it would travel along the edges of the creek and take a slow, leisurely trip downstream. Who knows?
Predicting the weather is like predicting where that football will end up. Meteorologists do very well, given the difficulties, but unexpected events can and do happen all the time in the atmosphere and at the earth's surface, making what was a correct assumption one moment an incorrect one the next.
Because weather includes so many variables, it is especially difficult to predict what the weather will do several days from now. The further into the future a meteorologist predicts a weather pattern, the more likely it is that the forecast will be wrong.
