PORTLAND, Ore. (KOIN) — It’s getting close to that time of the year when we are transitioning from that warm and sunny summer weather to a slightly crisp and, at times, cloudy fall sky.

We are officially starting meteorological fall on Thursday. You may be thinking that it still definitely feels like summer — and there is no doubt about that with the high temps we’ve been seeing.

But what does this transition mean for our weather? We are going to go from these toasty afternoons down to what will feel more like fall.

September 1 is the first day of meteorological fall, which has an average high of 80 degrees and an average low of 57 degrees. If you use the chart below, you will notice that we start to see about an eight to twelve-degree drop each month from this point on. The sun angle is lowering and we are losing the long summer days.

We also go from no rain to more consistent rain from September through November.

The graphic above shows another way to envision the temperature drop that is coming over the next 91 days.

If our current summer weather continues, we may miss out on all the beautiful lower 80s that we traditionally get during late August and early September. By the time we wrap up November, we are going to be sitting at an average high of 50 degrees. Who’s ready for changing leaves and all things fall? You may think of meteorological fall as the beginning of the fall conversation.

Did I mention that our average low temperature is in the upper 30s by the end of meteorological fall? You will need the winter gear ready by then. We will refrain from saying winter for the rest of this article.

We discuss the difference between both meteorological fall and the autumnal equinox below.


What exactly is meteorological fall and how is it different from our normal conversation about fall? For meteorologists and climatologists, we break down each season by the annual temperature cycle (the period of time that is warmest, coolest, and the transition months). This is a way to keep data consistent across the board. With that, we can define meteorological fall as a three-month collection of data for the months of September, October, and November.

It’s important to keep data consistent. This is what is difficult with using the astronomical fall as a period of recording. Due to the leap year and the inconsistency of when each season starts and ends each year, it makes it less organized for keeping stats.

Astronomical fall is based upon where the natural rotation of the earth is in relation to the sun. This year the autumnal equinox lands on September 22. This is how humans have been gauging the changing of seasons for ages. We have two equinoxes and two solstices.

Check out the chart below to get a clear-cut idea of the two below.