All Weather News

How Winter Works

15 Nov 2017, 1:04 pm

When I hopped in my car this morning, I found myself overcome by the icy chills of the changing season.
As I gripped the icy steering wheel, my visible breath coated the windshield and I found myself desperately asking, “why?”

But as a scientist, I already knew the answer.

Tilt of the Earth

Contrary to popular belief, the changing of seasons has nothing to with our distance from the sun. In fact, we are actually closest to the sun during winter in the Northern Hemisphere.

The changing of seasons is actually caused by the tilt of the earth.
Think of Earth like a spinning top, whirling through space. The poles are what the earth spins around, but there is a tilt to the spin. As a top would wobble as it spins about on a flat surface, the earth slowly wobbles through space. We are a tilt in that wobble, so instead of being perfectly upright– there is always a part of the earth pointed at the sun.

That tilt is the reason seasons exist. During the Summer Solstice, the North Pole is tilted toward the sun. But as the earth orbits the sun, the North Pole tilt starts to face away from the sun. Days get shorter and temperatures drop as we near the Winter Solstice. Or when the North Pole is tilted farthest from the sun.

Changing Jet Stream

The changing intensity and duration of sunlight caused by the tilt of the earth, has major affects on our weather.

Weather is largely controlled by the jet stream. This fast-moving current of air high in the atmosphere overhead that separates cold arctic air to the north and warm tropical air to the south.

Keeping things over-simplified. The area of greatest temperature contrast is where the jet stream typically sets up.
During the summer months, the Polar jet stream shifts north. It also remains fairly zonal or flat. This also allows the Subtropical jet stream to travel in a zonal pattern across the southern continental U.S.

As the Northern Hemisphere tilts away from the sun, the Northern most latitudes lose the daytime heat source of the sun. This allows the Polar jet stream to shift south as cooler temperatures take over.

Changing Weather

Jet streams affect the weather we see every day. Though it isn’t a surface feature, it plays a big role in the surface features we see.

Lows form in troughs in the jet stream while High pressure forms in the ridges.
Here’s a look at an above map with surface pressure centers imposed:

This is a big reason we see a change in general weather patterns between summer and winter.

The shifting jet stream location also helps fuel severe weather during both spring and fall.
It’s a combination of clashing air masses, upper-atmospheric support, and a whole lot of other little weather quirks— so we’ll just save the ‘why for another article.

For WeatherNation — Meteorologist Jeremy LaGoo

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