Weather in the Foothills

“And the sun took a step back, the leaves lulled themselves to sleep, and autumn was awakened.”
~ Raquel Franco, contemporary American poet

The first snow of the 2018-19 season fell across Montana’s Glacier National Park a little over two weeks ago. While we can’t boast of a winter wonderland, we do have our tell tale signs of autumn’s approach. The most noticeable of these is the ebbing duration of daylight. Liked by few, the effects on both man and beast are inescapable. Sorry…

On Sept. 22 autumn begins and no matter where your location on Earth, the day will be approximately 12 hours long. Around this time, those in the Northern Hemisphere begin to observe the days getting shorter, although this began on June 22, the day after the year’s longest day. Interestingly, the speed at which daylight is dying is faster now than at any other time of the year.

The daily change in the amount of daylight differs dramatically by latitude at this time of year. On the equator, the rate of change is essentially zero – on Sept. 21 the day will be about 12 hours long as will the following day. As you trek north, that rate greatly changes. Along the way, in La Crescenta there is a -2:06 light loss. Arriving at Barrow, Alaska – within the Arctic Circle – the length of daylight is cut by 10 minutes a day. You may ask what is the importance of such facts. Light is a signal to animals, plants and, before the light bulb, people of the seasons’ changes. It affects creatures living at high latitudes as light dictates their biology. Reproduction must be carefully timed; it’s a matter of survival.

Humans and other mammals possess an internal clock that governs sleep/wake cycles and other daily functions. Light provides nonvisual cues that influence pupil dilation, alertness, melatonin levels and heart rate modulation, according to biologists. Light receptors in the retina of the eyes pass along these “nonvisual cues” to reset our circadian rhythm or the physiological 24-hour process within living things – even fungi!

Everybody’s clock doesn’t tick on a 24-hour rotation, however. The average human day – as generated by the suprachiasmatic nuclei in the hypothalamus of the brain – our primary circadian pacemaker – lasts about 24 hours and 11 minutes. Light “resets” this internal clock and our bodies become synched with the time of day.

Good God, the complexity! Over the next month, we lose an additional one hour and eight minutes. The loss of daylight continues on until the winter solstice.

Daytimes are expected in the 80s, nights in the 50s and a pumpkin on the hearth – autumn is awakening!

Sue Kilpatrick is a Crescenta Valley resident and Official Skywarn Spotter for the National Weather Service. Reach her at suelkilpatrick@gmail.com.