Yesterday was the Vernal Equinox. Many people call this the first day of spring without thinking much about it. Can spring start at the same moment everywhere on Earth?
Think about the equatorial regions. At the equator, March and September are when the sun is directly overhead at noon. It is hot all year at the equator. But it is often hottest in March and September.
The weather is also rainiest and most humid along the equator around the time of the equinoxes because the direct sunlight causes peaks in evaporation rates to go along with the peaks in temperature. Around the time of the Solstices in winter and summer, the middle of the world has its two slightly less hot seasons.
So there are relationships between the equinoxes and weather, but they are general and varied around the world. The Vernal Equinox is really an astronomical moment with no immediate impacts on the weather anywhere.
This makes the "first day of spring" a fairly useless concept.
