“There is a harmony in autumn, and a luster in its sky, which through the summer is not heard or seen, as if it could not be, as if it had not been!”
~ Percy Bysshe Shelley, poet

What are you doing tomorrow, Friday, Sept. 22 at 1:02 p.m. PDST? One of the greatest (celestial) shows on Earth will arrive, ready or not. It’s free of charge and elephants are not used for the event. Every year, at this time, the Autumnal Equinox occurs. At this exact moment summer ends and autumn begins.

This year, in particular, red carpets need to be rolled out and trumpets blasted as, weather-wise, the timing couldn’t be better for autumn’s arrival. A cold Canadian air mass began to settle in midweek bringing cool and breezy winds. Today, Thursday, a major temperature drop accompanied by the possibility of precipitation for Los Angeles is in the forecast. How are these conditions different from summertime? The origin or source of the moisture is not a “monsoonal flow” or “night and morning low clouds,” which are typical during the summer in Southern California. Storms forming and moving south out the Gulf of Alaska or Canada (as we are expecting) are winter-type systems.

While our Verdugo Mountains were ablaze over Labor Day weekend, the National Weather Service issued the first winter storm warning of the season. The first snow flurries dusted the higher elevations of the Rocky Mountains. Butte, Montana began reporting snow just a few hours before a report of fire was made in La Tuna Canyon. Both are very typical almost-fall scenarios; not much new under the sun here. The following would fall into the same category, but remains unbeknownst to many of us. Back to equinoxes … and a fascinating and related phenomenon.

On the equinoxes (Vernal-spring and Autumnal-fall) the Sun shines directly over the equator at noon. As a result, there are 12 hours of daylight and 12 hours of darkness, equally everywhere on Earth. This effect gives rise to the name assigned to this date – equinox – that is formed from the Latin word for “equal night.” Upon reading everything I could possibly understand (and not understand) without being an astrophysicist, I came across a most noteworthy natural occurrence.

I chose Ecuador as a location on the equator because it lies directly on the imaginary line and has amazing tropical beaches. From their sands, as would be true from any equatorial point on the globe, you can watch and experience the quickest sunsets and shortest twilight periods. Throughout history, journals kept by world travelers give document to such observation, “Darkness falls almost instantly after sunset; there is almost no twilight.” Why?

Hopefully the good question has a good answer, as the reason gets a little complicated to understand. The simple answer is at low latitudes (those closest to the equator), the sun sets perpendicular to the horizon, i.e. goes straight down, and at higher latitudes, the sun sets at a more oblique angle, allowing it to remain close to the horizon after sunset. The closer the sun is to the horizon, even if dipped below, its rays shed visible light into the atmosphere, thus a longer twilight period. The magical time between sunset and darkness is 30 minutes longer in La Crescenta than in Ecuador.

There’s a 40% chance for rain tomorrow and by next week Santa Ana winds and a significant warm up are on the weather docket. Summer is technically over, although its weather may linger through autumn. Change is in the wind!

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

  Sue Kilpatrick