How to tell the weather of a day?

There is no basis for distinguishing weather by temperature difference. If it is sunny or rainy, it can be distinguished by air pressure, because the temperature changes at any time in a day with the change of the sun's altitude angle and cloud cover. Of course, the weather forecast of various technologically advanced mobile apps is actually very accurate, and it can be updated in real time, and the forecast of the future is also very accurate.