Shorter days help bring out the colors of fall

Hopefully you’ve taken the time to notice the beautiful fall colors that have painted the Inland Northwest landscape over the past several weeks. It is the combination of the vibrant-colored foliage and ever-cooling temperatures that seems to get most folks into the autumn spirit.

Surprisingly, though the plants themselves do respond to the types of fall weather that Mother Nature brings – whether it be unseasonably warm or cool, wet or dry – there is another variable that plays a much more significant role in bringing out the color of the season.

You have probably noticed how much darker it is around the dinner hour these days. After a peak of nearly 16 hours of daylight on the summer solstice, we are now down to less than 11 hours of daylight.

Unlike temperatures, the number of daylight hours we enjoy follows a predictable pattern, year after year. It is the onset of these shorter days and longer nights that most greatly influence the timing of color change and leaf fall.

Chlorophyll, the substance which gives the leaves their green color, absorbs sunlight in the process of photosynthesis. During photosynthesis, plants convert carbon dioxide and water into oxygen and glucose. As the days get shorter, production of chlorophyll slows down, and eventually stops, leading the way for other pigments to shine. Carotenoids are responsible for the yellows that we see in the leaves, while anthocyanins produce the shades of red. The intensity of fall colors, if not the timing, is strongly influenced by the weather. A succession of warm, sunny days and cool, crisp but not freezing nights results in the best color.

Local weather statistics

It has been a relatively cold and dry first half of the month. In Spokane, 11 out of the first 16 days saw below-normal temperatures. Spokane was 3 degrees off a record low last Sunday when the mercury dipped to 22 degrees. Coeur d’Alene’s low that morning of 23 degrees did break the previous record low of 25 degrees set back in 1969. Hard to believe the month started off with highs in the 80s.

Despite the killer freezes, we haven’t been surprised by any early-season snows, as things have been pretty dry across the region. As of Wednesday, Spokane had only measured .27 inches of rain in a month that normally receives just over an inch. Coeur d’Alene has received a bit more precipitation, .49 inches, but normally gets around 2 inches each October.

Although there hasn’t been any snow, I did experience a pretty good downpour of graupel in the Greenacres area on Oct. 9, which momentarily coated the ground white and caused temperatures, which were in the mid-50s, to plummet an easy 10 degrees or more. On average, the Spokane/Coeur d’Alene area sees less than half of inch of snow in October.

The upcoming week should be a roller coaster of temperatures from mild to chilly. It looks like a decent rain- and windstorm will start off our work week, with drier conditions following.