How do meteorologists know what the weather will be in the future?

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Even a week plus into the future…

In: Earth Science

They have very sophisticated programs that take decades of previous weather patterns and compare it to current weather patterns. Based on what is happening now the program (known as a model) gives you a handful of future weather patterns that are likely to occur from the current state.

Basically, past performance = likely future outcome. The further out into the future you go, the more possible outcomes there are which is why long term forecasts can be pretty inaccurate.

A weather system checks the current and recent weather situation. Based on what recently happened it calculated what might happen, by comparing it to all similar systems that have been recorded in the past. Based on that calculation, the weather systems gives a model. There are dozens of different models all with a different calculation.

A meteorologist basically compares those models to see what the most likely outcome is, because most models are pretty similar. The meteorologist I used to work with, used about 50 different models to make a prognosis.

Also worth noting, the more weather stations are connected to the model, the more accurate it will be. Cause a low pressure area a thousand kilometers away can have an effect on the development of the weather on your current location.

Source: I used to work with a meteorologist a lot.

In very broad terms, wind, rain, and temperatures are “caused” by the rotation of the Earth, by the Sun’s energy hitting the Earth and warming it up, by and geography (mountains may “push up”, redirect, or block winds, for example).

Geography doesn’t change much from day to day / year to year, and the Earth’s rotation and orbit around the Sun, and the Sun’s energy output, all of these are “predictable” from year to year. We do get the seasons after all, it’s more or less predictable.

Also, there’s an understanding of clouds and how the bigger storms (hurricanes etc.) are affected by heat and humidity and winds, and we do have radar and satellite systems that can track clouds and rain-fall, so basically it’s possible to make predictions as far as where a large cloud or a large storm system may move, and how it will affect the weather in its path.

So part of it is a matter of perspective: you go outside and see a clear sky and just sunshine, but for example the astronauts on the space station can see that big storm coming towards you for days before it finally gets to you. A satellite or radar view from above, combined with multiple weather stations sharing information about the weather that they “see” locally, basically you can calculate globally where the big storms / weather fronts are, and how they’re going to move for the next few days, and thus where it’s going to rain and so on.

An English admiral 160 years ago founded the Meteorological Department of Board of Trade and was the first to be financed by the government and could predict the weather patterns with a few hours in advance. The data collected in coastal towns was telegraphed to the MDBT London Office, when a storm was nearing land, he could issue an alarm to the closest port where an alarm was raised in the harbour. Nowadays meteorologists use computer simulation, matemathics calculations and sensors to measure and predict the weather.