© Unsplash/Gavin Allanwood
Whether it's in the morning when you wake up or in the evening just before going to bed, you probably check the weather application on your smartphone. Is it going to be cold? How should you dress? Should you be careful not to forget your umbrella? Being interested in the weather is a reflex for many people. But you have surely noticed that from one site or application to another, the forecasts are not the same. Sometimes the difference is small, but sometimes the gap is larger. It’s impossible to understand anything!
To predict the weather, weather sites and applications all have the same data, whether transmitted by satellites, airliners, ships at sea, buoys or terrestrial measurements. But then, they rely on forecasting models as well as algorithms. Obviously, there are several.
Differences in weather reports
If the data is the same, the applications and sites use forecast models which do not benefit from the same settings. Thus, there is the European CEPMMT model (or ECMWF in English), the French ARPEGE model or the American GFS model. It is the European model which is considered the most reliable of all. We also note different algorithms which integrate geographical realities.
Applications like Accuweather, Windfinder or even the weather application on your iPhone are all based on the American GFS model. On the other hand, Météo France relies on the French ARPEGE model. By using local rather than global data, the site is able to offer more precise details to its users. For its part, the Windy application leaves the choice of the forecast model used to Internet users.
But these are not the only reasons which explain these differences. Because you have to know how to interpret these models, maps and data! This is the role of forecasters. Human analysis is essential to obtain relatively accurate forecasts. Applications like the default one on your smartphone generally just provide raw forecasts, without any human interpretation.
Thus, such applications are relatively reliable in the short term, but that's another a pair of sleeves when it comes to seeing further. For more accurate long-term forecasts, it is in your best interest to consult sites like Météo France, which are not based on the American GFS forecast model and which rely on human interpretations of the data.