The fall equinox is on Monday, September 23rd, a month away. That’s when our day length will be just 12 hours and a handful of minutes. Currently, our day length is about 13 and a half hours but we are losing over 2 and a half minutes of daylight each day.
You may have noticed that our sunsets are now before 8 pm and the sun won’t return to setting that late until about April 23, 2020. Our sunrises on the other hand won’t be until after 6:30 am by the end of the month.
Now that we are losing our primary energy source, the sun, at a rapid rate, our temperature fluctuations will become more “system driven”. As Canada loses sunlight at a faster rate than us, temperatures will rapidly decline there. Any incoming cold fronts will deliver increasingly colder air. Warm fronts will help to bring temperatures back up a few days after a cold front and the cycle continues.
In the fall months though, the cold fronts will often overpower the warm fronts. This is because the cold canadian air is getting colder and colder while the warm air only gets a little cooler. It is not an even change. Plus the sun alone will not be sufficient enough to warm temperatures much. It becomes increasingly difficult for our temperatures to stabilize and thus, our normals drop rapidly through the fall season. For more on how our climate normals change heading into fall check out this similar article here.
We often will see big differences in temperatures every few days with a stretch of 2-3 days with highs in the upper 70’s/lows mid 50’s and then a warm front passes with 1-2 days of temperatures in the mid 80’s/lows in the 60’s, then finally a cold front passes that will drop our lows to the upper 40’s/highs low 70’s until our temperatures can’t recover and slowly drop (these are hypothetical numbers). If we plotted our average temperatures in summer vs fall, there would be more variance in the fall, similar to spring vs. summer in the image above which shows temperatures for winter, spring and summer.