The First Day of Fall was Sep 1? Try Again!

[canyonwalker]

Last week I noticed a flurry of headlines in my newsfeed about how "It's Fall Already And...."

"LOL, no," I thought. Fall in the Northern Hemisphere begins on September 21 or 22 each year, at the time of the autumnal equinox. This year it's the 22nd. What's the deal with people trying to start fall on September 1? I know words like "autumnal" and "equinox" are hard for the average person to comprehend, but is remembering the number 22 also a bridge too far?

Today I finally had a chance to look up why people were saying fall started last week. It turns out that using the autumnal equinox as the start of fall— the way we were all taught back in grade school— is known as astronomical fall. Meteorological fall simplifies the seasons to start on the first of the month. Meteorological Fall is September 1 - November 30.

Now, if you thought words like autumnal and equinox were hard, let's break down what astronomical and meteorological mean. Astronomical = relating to objects in space. In this case, the point in the earth's annual orbit around the sun when day and night are of equal length. Meteorological = relating to weather. As in, let's say fall starts in September because suddenly the weather turns cool. Except... NO IT DOESN'T!

Anyone in the US who's not living under a rock right now knows that half the country in the grip of a record breaking heat wave. And if you are living under a rock... well, likely it's because you know how hot it is and are under there for shade. 🥵 After yesterday's record setting heat of about 103° F in Sunnyvale (I've seen reports between 102-109 depending on location) today was even hotter at 106° F (41° C). Previous records were 99°. The average for this time of year is comparatively pleasant at about 81° F (27° C).

While the record setting heat wave is particular to this year, warm Septembers are not. September normally starts out warm. Yeah, it ends cooler. So, meteorologically, the marker for fall belongs in mid- to late September. Maybe even... September 22nd?

Comments

[kjn]

Sweden's meteorological definition of autumn for a given year: a daily average temperature between 0 and 10 degrees Celsius lasting for five days, and falling after August 1. Autumn will then be counted from the first of those days.

[canyonwalker]

Hmm. That's an observational definition. It's definitely worthwhile for recording when something has happened, but it's only usable in hindsight. In that respect it's similar to how I gauge when Autumn has started, e.g. Pants? and The Heat Is On!

[kjn]

Yup. A similar definition is also used as a basis for judging the normal day that autumn begins. The very northern part of Sweden normally gets autumn in August (some parts of the mountains even go directly from meteorological spring to meteorological autumn), but for most of the country it happens between over a month, from early September to early October.

[sorcyress]

Heh. I'm on the half of the country where it *has* turned into meteorological fall --gentle rain and cooler temperatures the last few days in Boston! And I'm definitely a believer that December 1st is the start of winter (though not often convinced that March 1st is the start of spring.)

~Sor