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WEATHER 101: Snow Friday and 60 degrees Monday. How does that happen?

Weather Blog

BREAKING NEWS: It’s March in WNY. Weird things happen with the weather. If there’s one constant, it’s change. Anyone who has lived here long enough has learned to accept it, regardless of whether you like it. But have you ever wondered exactly HOW our weather can change so abruptly? Case in point, we expect temperatures to drop into the 20s Saturday night and climb to 60 Monday afternoon. We could be looking at 36 degrees in 36 hours, which is no small feat. What has to happen to be able to pull that off?

EARTH! Well, more accurately, the rotation of the Earth. Realize it or not, you’re moving. Fast. At the equator, the Earth’s spin is about 1,000 mph. I know what you’re thinking; “Eric, I’m pretty sure I’d be able to feel something if I was moving at 1,000 mph”. It’s true. You, the dog, the trees in the yard and the air around you is all moving at 1,000 mph. And that’s the catch. With everything around you ALL moving at the exact same speed, you have nothing to compare it to. Relative to you, the air is moving at the same speed as you are. That means…no wind. When you’re in a car, you know you’re moving because you can stick your head out the window and feel the air rushing past you. Or, you can see houses zipping by as you travel. But if that air is traveling at the same speed, or those houses had legs and ran alongside you at the same speed, you’d never know the difference. Two cars traveling at 60 mph make no forward or backward progress. You can ride window to window with it. Relative to each other, you can conclude they’re not moving. Yet they are, at 60 mph. As long as Earth’s rotation remains steady (no speeding up or slowing down), you won’t feel any force. So here you are, sitting at your desk reading this while breaking the speed limit. You rebel, you.

WHAT DOES THAT HAVE TO DO WITH OUR WEATHER? A lot. Remember I said the Earth rotates at 1,000 mph at the equator. The farther you move poleward (both north and south), the slower that speed. In fact, at the poles the speed is zero.

While this might seem like a useless tidbit, it plays a crucial role in our weather. Given this difference based on latitude, air in the northern hemisphere gets deflected to the right. That’s a major part in how our weather works. Here’s a cool visualization of this effect: https://www.youtube.com/watch?v=HIyBpi7B-dE

Consider air spiraling into an area of low pressure. Instead of arrows pointing straight into the center of that low, the air gets deflected to the right, inducing rotation, or spin. In our half of the world, air moves counter-clockwise with low pressure systems and clockwise with high pressure, like this:

Given this fact, weather can do a whole lot of funky things based solely off of which side of high or low pressure you’re on. On Saturday, high pressure will be west of Rochester. Clockwise flow will funnel cold, Canadian air across WNY. Translation: Cold day.

By Monday, that same high rapidly slides to the coast off the Carolinas. For us, that means WIND SHIFT!

The simple act of switching sides dramatically alters our temperatures as the source of the air switches from Canada to the Gulf of Mexico. And voila, you have 36 degrees in 36 hours.

DOES IT ALWAYS WORK LIKE THAT? There are rare instances when small scale areas of low pressure, like tornadoes, are able to bend the rules. You can find cases of anti-cyclonic tornadoes, or those that rotate opposite what you would expect. It takes very special circumstances, such as the splitting of supercells, to pull this off. Sometimes, you can have twin tornadoes in which one rotates one way and the other does the opposite. In my 8 years covering tornadoes in Alabama, I can’t recall a single instance of an anti-cyclonic tornado. But, they have been documented.

The next time you see a meteorologist talking about an area of low pressure, pay attention to which way it’s spinning. You’ll find they all do the same thing. Ever seen a clockwise spinning hurricane? They’re out there…but only in the southern hemisphere. They do weird things in the southern hemisphere. Word on the street is it’s actually Summer there. Weird, right?

Chief Meteorologist Eric Snitil

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