The weekend takes a turn to wet and cool weather; Sunday’s highs 20 degrees cooler than Saturday’s summery weather

The Equinox (Vernal & Autumnal)

From the National Weather Center:

There are only two times of the year when the Earth’s axis is tilted neither toward nor away from the sun, resulting in a “nearly” equal amount of daylight and darkness at all latitudes. These events are referred to as Equinoxes.

The sun angle continues to decline as the Northern Hemisphere tilts away from the sun, leading to the winter solstice in December when the sun reaches its lowest point in the sky. This results in the shortest day and longest night of the year.
After the winter solstice, the sun angle begins to increase again as the Earth tilts back toward the sun. This change marks the transition from winter to spring, leading to longer days and higher solar angles.