Why Meteorological and Astronomical Seasons Don’t Line Up

iStock
iStock

For many Americans, summer essentially starts after Memorial Day weekend. The school year's wrapping up, offices seem emptier, and jorts re-emerge from the depths of our closets. Yet the calendar says differently.

Technically, summer doesn’t start until after the summer solstice, usually around June 21, when most of us are already well into backyard barbecue season. But meteorologists define summer as the season running between June 1 and August 30. Why the disconnect?

There’s a difference between meteorological summer—shorts weather—and astronomical summer, which is based on where the Sun is positioned in relation to the Earth, as Weather Underground explains.

Over the course of the year, the tilt of the Earth means that one hemisphere is closer to the Sun than its counterpart for several months at a time, marking the summer season. When the Northern Hemisphere is closer, from late June to late September, the northern part of the world experiences summer, while the Southern Hemisphere—which is tilted farther away from the Sun—experiences winter. During summer months, the Sun takes a longer path across the sky, resulting in longer daylight hours. The equinoxes mark the days where the ratio of day-to-night stands at exactly 12 hours each, because the Sun is lined up with the equator.

Because the Earth doesn’t take exactly 365 days to travel around the Sun each year, the days that equinoxes and solstices fall on vary slightly year-to-year. Still, they typically take place around March 21 (spring equinox), June 21 (summer solstice), September 22 (autumnal equinox), and December 22 (winter solstice).

That variability makes it difficult to pin the seasons to calendar dates, so we have meteorological seasons. These are the times we normally think of as summer, fall, winter, and spring—the three-month chunks of time that correspond to the changes in the weather. Meteorological summer runs from June 1 to August 31, corresponding to how most people envision the season, running from about Memorial Day to about Labor Day. Fall goes from September 1 to November 30, winter from December 1 to February 28, and spring from March 1 to May 31.

The firm dates of meteorological seasons allow weather forecasters to better observe and predict weather patterns year-to-year, since they’re based on the annual temperature cycle, rather than the exact timing of the Earth’s orbit. Even if daylight hours aren’t yet at their peak in early June, temperatures are still more akin to summer than spring, so it makes sense to call it summer from a weather perspective. When it comes to compiling statistics on temperature and weather patterns for agricultural planning and business, working around the static calendar is a lot easier than trying to deal with the variability of the Sun’s position in the sky.

So yes, even though summer doesn’t technically start until June 21 at 12:24 a.m. Eastern Time, you and your jorts were onto something after all.

[h/t Weather Underground]

Denver's Temperature Dropped a Record 64 Degrees In 24 Hours

Leonid Ikan/iStock via Getty Images
Leonid Ikan/iStock via Getty Images

One sure sign summer is over: On Wednesday, residents of Denver, Colorado were experiencing a comfortable 82-degree day. Just before midnight, the temperature dropped to 29 degrees. Between Wednesday and Thursday afternoon, the Denver airport recorded a differential of 79 degrees down to 24 degrees. At one point on Wednesday, a staggering 45-degree drop was seen in the span of just three hours.

All told, a one-day span saw a 64-degree change in temperature, from a high of 83 to a low of 19, a record for the state in the month of October and just two degrees shy of matching Denver’s all-time record drop of 66 degrees on January 25, 1872. On that date, the temperature plummeted from 46 degrees to -20 degrees.

Back to 2019: Citizens tried their best to cope with the jarring transition in their environment, to mixed success. On Wednesday, the city’s Washington Park was full of joggers and shorts-wearing outdoor enthusiasts. Thursday, only the most devoted runners were out, bundled up against the frigid weather.

The cold snap also brought with it some freezing drizzle which prompted several vehicular accidents, including 200 reported during Thursday's morning commute. It’s expected to warm up some in the coming days, but residents shouldn't get too comfortable: Melting ice could lead to potholes.

[h/t KRDO]

Fall Foliage Is Running Late This Year

Free art director/iStock via Getty Images
Free art director/iStock via Getty Images

The August arrival of the pumpkin spice latte might have you feeling like fall is in full swing already, but plants aren’t quite so impressionable. According to Travel + Leisure, the best fall foliage could be coming a little later than usual this year.

Historically, the vibrant transformation starts to sweep through northern regions of the Rocky Mountains, Minnesota, and New England in mid-September, and reaches its peak by the end of the month. Other areas, including the Appalachians and Midwest states, don’t see the brightest autumn leaves until early or mid-October. The Weather Channel reports that this year, however, the forecast from the National Oceanic and Atmospheric Administration predicts unseasonably warm temperatures for the next two weeks, which could impede the color-changing process.

Warm temperatures aren’t necessarily bad for fall foliage, as long as they occur during the day and are offset by cool nights. Since meteorologists don’t expect the overnight temperatures to drop off yet, plants will likely continue producing enough chlorophyll to keep their leaves green in the coming days.

The good news is that this year’s fall foliage should only be about a week late, and meteorologist David Epstein thinks that when leaves do start to change color, we’re in for an especially beautiful treat. If the current weather forecast holds, he told Boston.com, we'll "see a longer season than last year, we’d see a more vibrant season than last year, and it would come on a little earlier than last year, which was so late.”

Though poor weather conditions like early snow, heavy rain, drought, or strong winds can cause leaves to fall prematurely, most trees right now are in a good position to deliver a brilliant display of color after a healthy, rain-filled summer.

Find out when you’ll experience peak fall foliage in your area with this interactive map.

[h/t Travel + Leisure]

SECTIONS

arrow
LIVE SMARTER