Temperatures cool as summer turns into fall
It is hard to believe that summer is almost over. The autumnal equinox, the day the fall season begins, falls on Sept. 23 at 2:51 a.m. this year. Looking back at summer, we can summarize it from two different perspectives. On one hand, the nearly endless stretch of warm to hot, sunny days made it perfect to enjoy a myriad of outdoor recreation. On the other hand, lack of precipitation and some scorching days stressed many lawns and gardens, and more importantly created dangerous fire weather conditions and pushed much of Idaho into a serious drought situation. Coeur d’Alene saw 30 afternoons where temperatures rose to 90 degrees or higher, and four of those days reached or exceeded 100 degrees. A drier than normal July was followed by a month with only three days of measurable rainfall. The first half of September has been completely rainless, and we continue to suffer a rainfall deficit of more than 2.5 inches for the year.
The good news is, along with a change in season, we should see a change in the weather to a cooler and wetter pattern for the second half of the month.
Most of you probably learned in school that we have seasons because the earth is tilted on its axis by approximately 23.5 degrees. In our summer, the northern hemisphere is tilted toward the sun, allowing us to receive more direct solar radiation. In our winter, the northern hemisphere is tilted away from the sun, making for shorter days and a lower sun angle. Distance from the sun has nothing to do with seasonal changes in temperature, as we are actually closer to the sun during our cold season. On the equinoxes of both spring and fall, a person standing on the equator would see the sun pass directly overhead. Likewise, these two days are the only days when the sun rises due east and sets due west. You might have heard that on the equinoxes, day and night are exactly 12 hours long. This is almost true, as sunrise in Coeur d’Alene on Sept. 23 is at 6:35 a.m. and sunset occurs at 6:43 p.m. The reasons the times are not exactly 12 hours apart are complex and have to do with how the time of sunrise and sunset is determined, and the fact that the sun is not a singular point in space. We do get very close to equal night and day on Sept. 25, when sunrise occurs at 6:38 a.m. and sunset at 6:39 p.m.
Seasonal changes are more drastically felt the farther you go from the equator. At areas near the equator, such as in Indonesia and Equador, there is little variation in temperature from one part of the year to the next, and the number of daylight hours is nearly constant. Much more substantial changes in daylight hours and the angle of the sun occur in Coeur d’Alene which is situated at approximately 48 degrees north. We definitely experience major differences in our weather from one season to the next. The ultimate in seasonal changes, however, occurs from the Arctic Circle to the North Pole, where summer means 24 hours of sunshine, while winter plunges you into 24 hours of darkness.
In North Idaho, the fall season will bring an increase in precipitation, though we will still get to enjoy many days of sunny, mild afternoons followed by crisp cool nights. Our average high on the first day of fall is 71 degrees with an average low of 43 degrees.