Why does Windy.com change forecasts retrospectively?
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Why does Windy.com change forecasts retrospectively?
I've taken screenshots of a forecast for let's say 16th and 20th of the month and when the forecasted weather changed noticably on the 18th I notice the forecast for the 18th - 20th has changed, this is all to be expected, but when I look at the past forecast from 16th and 17th I notice it too has changed retrospectively and no longer matches the screenshots of past forecasts. Why?(It's been a while since I documented this so if you need evidence I can go back through photos and find that or just recreate it because I've documented this more than once. At this stage I'm assuming it's not a glitch and Windy.com are aware and can explain it so no point me going to the effort of providing evidence, but I will if needed.)
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@SkyDJedi
What do you mean by retrospectively ? Windy does not show past data. But shows the forecast from the more recent update of the weather model.
Today the computer of the weather center, for instance ECMWF, starts the calculation of the 15-day forecast at 00 UTC (reference time) and provide the data about 8 hours later. With this data Windy update maps and tables (at update time). The computation by the weather model is using millions of observed data throughout the world (weather stations, radiosondes, airplanes, ships and mostly satellites).
6 hours later the ECMWF starts a new computation based on new observed data. So this new computation provides a forecast that could be slightly different for the current day and more different for the following days.
https://en.m.wikipedia.org/wiki/Numerical_weather_prediction
