Meteorological Winter: Why Meteorologists Call Dec. 1 The Start Of Winter

Why Alaska’s Rivers Are Running Orange

Meteorological winter arrives Monday, but you may wonder why this is happening weeks before the winter solstice.

The winter most are familiar with: The date on your calendar when winter begins is known as the winter solstice. In 2025, that will occur on Dec. 21, at 10:03 a.m. ET.

That's the moment in time when the sun's most direct rays are shining farthest south on the Earth, directly over the Tropic of Capricorn. It's when the Northern Hemisphere is tilted farthest away from the sun.

How most define the seasons: The changing sun angle through the year due to the tilt of Earth's axis as it revolves around the sun is why we have what are called astronomical seasons.

The winter solstice signals the start of astronomical winter, which lasts until the vernal (spring) equinox, occurring March 20 or 21 each year.

In winter, the sun rises in the southeast and sets in the southwest, a much shorter path across the sky, which is why the length of daylight is significantly shorter, usually only eight to nine hours.

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Meteorologists do this differently: When you examine average daily high and low temperatures through the year, you'll quickly notice a pattern.

The coldest three months of the year in the Northern Hemisphere are usually from the beginning of December through the end of February, while the warmest three months are typically from the beginning of June through the end of August.

These temperature buckets don't line up nearly as well with the astronomical seasons. For example, the meteorological conditions often associated with winter more often occur before the Winter Solstice across much of the Northern Hemisphere. Moreover, climatology would imply that spring-like conditions often occur well before the Spring Equinox in Late March.

How do the two seasons compare? Alaska-based climatologist Brian Brettschneider calculated that the Dec. 1 through Feb. 28/29 meteorological winter is a better fit to the coldest time of year in most of the United States and Canada.

In an analysis of dozens of U.S. cities, Brettschneider found only Honolulu, Hawaii, had its coldest 90-day stretch extend deep into March.

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For those who live in the northern U.S., this makes sense.

It seems silly when we say "winter is here" just days before Christmas, when many parts of the North have already had at least one significant snowfall or cold snap.

Another advantage to meteorological seasons is the ease of calculating seasonal statistics, since every meteorological season starts on the first of the month.

Hayden Marshall is a meteorologist intern and First-Year Master's Student at the Georgia Institute of Technology. He has been following weather content over the past three years as a Storm Spotter and weather enthusiast. He can be found on Instagram and Linkedin.