Spring in the meteorological sense ...

In the meteorological sense, spring is defined as: if the daily average temperature of five consecutive days in a year (in the northern hemisphere) is greater than or equal to 10 degrees Celsius for the first time (the daily average temperature is the average of local temperatures at 2: 00, 8: 00, 14: 00 and 20: 00), the first day is taken as the start date of spring.

But spring is a mixed season, sometimes cold air invades, and the temperature often drops sharply. So in some places, another item has been added: even if there are days below 10 degrees, it cannot last for more than five days in a row. Otherwise, it's not beginning of spring.