Welcome to autumn; welcome to mid October like weather. Temps the next few mornings sinking into the 40s(about 10-degrees below normal)...yikes. Did you turn on heat?
Autumn is playing to a sold out fall festival like weather crowd that will accommodate the new season with sunshine and crisp chilly nights. The word equinox comes from the Latin words for "equal night." The fall and spring equinoxes are the only days of the year in which the Sun crosses the equator.
Why do the seasons change? Credit the tilt of the Earth. The Northern Hemisphere points away from the sun, causing shorter days and less direct sunlight. Sunlight is becoming more indirect which means longer shadows.
Daylight hours have been getting shorter since late June, however...the average temperature started declining...albeit slowly...in early August. The Earth will continue to tilt away from the sun...now at zero tilt...until the winter solstice in late December...the date of maximum tilt (23.4 degrees) away from the viewing area. As the Earth revolves around the Sun in its orbit, the north-south position of the Sun changes over the course of the year because of the changing orientation of the Earth's tilted rotation axes.
This tilting away from us can be tested. You will notice your shadows are getting longer on clear days...less direct sunlight...less sunburn. For kicks...you can measure your shadow once a month at the same time and see how they vary throughout the year. Yes...you need a sunny day.