How many days is the weather forecast reliable?

You are thinking about booking a beach next weekend, look at the weather forecast and realizes that everything is conspiring in your favor, indicating a lot of sun and clear weather. But then, on the day of his walk by the sea, he realizes that a veritable deluge is happening outside. Whether for a beach, pool or any other activity, you've certainly come across frustrating situations like this.

It is not uncommon that after a few moments like this, we start to question the assertiveness of the weather forecast given by meteorological agencies. But in the end, can you trust the meteorology🇧🇷 How many days is the weather forecast reliable? We answer these and other questions in this post. Check it out!

How is the weather forecast performed?

The weather forecast begins to be done at weather stations. Only here in Brazil, the INMET (National Institute of Meteorology) manages more than 400 stations, in addition, 10 regional districts receive station information. However, this collection does not only take into account the data obtained in the national territory, but the information sent from different points around the globe – and even from outside it.

For this measurement, various types of devices are used, such as thermometers, barometers, anemometers, rain gauges, among others, to analyze variable information such as temperature, relative humidity, atmospheric pressure, rainfall volume, wind direction and speed, degree of insolation and duration. of action of the Sun.

Weather models vary, and each country or region may have its own. Of course, good models guarantee better predictions. Just as more and better equipment makes projections more accurate. But nothing is more decisive in trying to know what the weather will be like than the climatic characteristics of each region of the globe.

In addition, radars capable of analyzing the composition of clouds are used. They are very useful when you want to predict short-term weather conditions. In Brazil, 20 of these radars are launched per day, which go inside meteorological balloons, at a cost of US$ 200, according to data from the INPE (National Institute for Space Research).

In addition to meteorological stations, these devices are also installed on ships, planes and sounding balloons that record all weather conditions on continents, oceans and at high altitudes. For forecasting, satellites are also used. These send more accurate information since they have a view of the displacement of air masses. 

The logic of weather forecasting is still the same as when it first appeared in the 19th century: collecting as much data on the weather as possible, in as many places and times as possible, and extracting the best forecast from them. The difference lies in the new ways of collecting data, which have evolved thanks to the advancement of technology over the last few generations. In addition, numerical forecasts appeared, mathematical models that simulate the climate with greater precision.

Apparently, the weather forecast is not that important. However, it is relevant to society in its economic activities or even in people's daily lives. In agriculture, for example, the weather forecast is used for planning the planting and harvesting of crops and also to prevent the arrival of frost, hail and drought. In aviation, it is also extremely important, as weather conditions directly influence flights around the world.

Is the weather forecast reliable?

But can you trust the weather forecast for that weekend barbecue? Well, generally speaking, you can trust it. The truth is that it has improved a lot, going from 50% accuracy 25 years ago (the equivalent of flipping heads or tails) to current 90% accuracy for today and tomorrow🇧🇷 But the remaining 10% remember that meteorology is not an exact science.

However, on many occasions we look at the forecast for five or seven days and even two weeks ahead. Are they also as reliable? The answer is no. Currently, the weather can forecast for up to 15 days, but with different reliability percentages. The hit percentage for the weather over the next five days, for example, drops to 70%🇧🇷 Already for two weeks, the number is only 50%.

So, you already know that if your appointment is closer to happening, it's easier to trust the weather forecast. Now, if your activity is going to take place outdoors for more than seven days, it is worth being cautious and having a plan B in mind.

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Source: CPTEC.