(dramatic music) - One of the most awe-inspiring forces of nature is lake-effect snow.

This phenomenon is one of the main reasons why areas near big lakes, like the Great Lakes, get such remarkable snow storms.

Lake-effect snow occurs when cold air passes over relatively warm and moist air above a lake.

The warm water vapor rises quickly, freezes, and then falls as snow.

And often, it's a lot of snow.

In Buffalo, New York, lake-effect snow is a big part of our winter's reputation.

We even give nicknames to the storms.

There was the October Surprise in 2006, which brought us 27 inches of heavy snow.

(chuckles) That was fun.

And then in 2014, Snovember dumped seven feet of snow in Buffalo's southern suburbs, while mere inches fell just a few miles away.

Neighbors north of the band could see a wall of snow.

That's one of the wonders of lake effect.

Depending on where you live, a storm may deliver multiple feet of snow, or almost nothing at all.

Lae-effect snow storms can be difficult to predict because they could be affected by many factors.

But when the right conditions come together, it could be so wrong, unless you were hoping for a snow day.

Today we're going to explore the science of lake-effect snow and see why Buffalo is so often in its bullseye.

(playful music) Lake-effect snows are exactly what they sound like.

They're snow storms that result from the effect that a Lake has on the local weather.

And there aren't many places in the world that have the right ingredients to make it happen.

It's most commonly associated with the Great Lakes, but also occurs on the east shore of Hudson Bay, and even the west coast of northern Japan.

As large masses of cold air, usually from Canada, move south, they pass over the huge open waters of the Great Lakes.

Compared to the Arctic air above, waters of the Great Lakes are relatively warm.

If the winds and temperatures are just right, the air acts like a big sponge that sops up water from the lake.

As this warm air rises clouds form and narrow bands that could produce two to three inches of snow per hour.

Let's look at the key ingredients for lake-effect snow.

First we need a large, relatively warm body of water.

Check.

Next, we need an Arctic air mass.

Got that too.

A general rule of thumb is that temperatures at 5,000 feet above the ground must be at least 23 degrees Fahrenheit, or 13 degrees Celsius, colder than the lake temperature.

The larger the difference in temperature between the air and the waters, the greater the potential for heavy snowfall.

We also need winds blowing in nearly the same direction throughout the lower atmosphere.

The heaviest single snow bands usually occur when the winds align roughly with the longest access of a lake.

The wind direction determines the fetch, not the fetch you play with Fido.

Fetch is the distance that the wind travels over the open water surface.

The longer the fetch, the greater the amount of heat and moisture that can come from the lake.

And each Great Lake has a different optimal fetch direction.

For example, a west-southwest wind travels 30 miles across Lake Michigan, 60 miles across Lake Huron, and nearly 130 miles across Lake Erie.

The more optimal the fetch, the stronger the lake-effect snow band will become, because air travels over the lake for a longer duration, picking up more and more moisture.

So why does the snow pile up in some places but then bypass neighboring towns?

The lake-effect snow bands are much longer than they are wide.

The average width of a band is about 10 miles, while the length can range from 30 to 250 miles long, depending on how strong the winds are.

If the winds are strong, the heaviest snow falls inland.

If winds are weak, the heaviest snow falls near the lake shore.

Ultimately wind direction also determines where the snow bands set up.

So, for example, a southwest wind between roughly 250 and 280 degrees will hit south of Buffalo in areas like Orchard Park and Hamburg.

But if the wind direction is between 220 and 250 degrees, the bands will hit the north towns.

During the prevailing winds areas south of Buffalo receive much more lake-effect snow than locations to the north.

Conditions in western New York frequently align for the perfect lake-effect storm, crowning Buffalo lake-effect king.

Now that we have a better understanding of lake-effect snow, let's dive a little deeper into density.

So what is density?

It's the amount of stuff within a certain space.

The closer the molecules are packed together, the denser the material will be.

It is calculated by dividing mass by volume.

Density is what drives circulation in lakes and oceans and the atmosphere.

All right, let's see what happens when warm water and cold water collide.

On this side, I've added cold water, and it also had a little bit of blue coloring.

And on this side it's warm water so I've colored it red.

So we're going to remove the divider and let's see what happens.

(upbeat music) Look, what's happening.

The blue cold water is moving to the bottom and the red warm water's moving to the top.

This is because of density.

And temperature affects density.

The molecules in the cold water are more closely packed together and they have less energy to move.

The warm water is less dense and rises and settles on top of the cold water.

So how does this all connect to lake-effect snow?

Just like we saw with the water in the tank, warm air will rise relative to cooler air because it has lower density.

The energy for the formation of lake-effect snow comes from atmospheric instability.

Any process that warms the atmosphere from underneath can create this instability, just like when cold air streams across the warm lakes.

As the air near the water becomes warm and moist, it becomes less dense than the colder air above it.

This creates buoyancy causing the air to rise similar to a hot air balloon.

As the air rises it cools.

And if there's enough water vapor, it will freeze and create snow.

And that snow then falls out of the sky when the air mass hits the land.

And when the wind blows in the right direction over Lake Erie, generally from the southwest, that snow falls right on western New York.

With an average of 91.9 inches of snow each winter, some may think it's destiny that Buffalo is one of the snowiest cities.

But when you study the science behind the lake-effect phenomenon, you'll actually realize that it has a lot to do with density.

(upbeat music) We saw the role that density plays in lake-effect snow formation.

But if you're interested in learning more about density in action, check out our "Compact Science" viewer challenge.

We have a fun experiment that you can try at home where you can create a colorful density column by stacking liquids.

Get all the instructions on our website and be sure to share back your results in the comments.

I'm Sarajane Gomlak-Green, and you've been watching "Compact Science."

Until next time stay curious.

- [Announcer] "Compact Science" is funded by the Joy Family foundation.

- Okay, rolling?

Okay, all right.

When water, I did it again.

Warm, warm water vapor.

So how does this all connect to lake-effect snow?

Just like every, oh my goodness, why do I keep saying?

Why do I want to say that?

Anyway, okay, all right.

Okay, mulligan.

(cameraperson mumbles) All right, okay.