In terms of headline-making weather across the country, there isn’t much going on right now. A push of cooler air following a cold front brought the return of lake-effect snow to the Great Lakes region. This means snow measurable in feet for some downwind of the lakes; and others, just miles away, little to no snow accumulation.
A Mild Winter
One of the first comments on every story I write here at Weather Nation, no matter the topic, is something to do with global warming. Both sides of the argument chime in and the typical internet battle ensues. But This go around, I want you to ignore long-term climatology and just let me explain why warmer temperatures equate to more snow.
You read that right, our warmer-than-average winter means we will see more lake-effect snow.
Simply put, warmer temperatures equates to less ice coverage on the lakes. Compare our current coverage of just 6.2% to that of years past and you’ll see just what I mean.
I’ve attached a couple maps to help illustrate my point.
But Why Does This Matter
The mechanism that causes lake-effect snow largely depends on two temperatures.
The temperature of the air and the surface temperature of the lakes.
In order for lake-effect snow to form the air temperature must be significantly colder than surface temperature of the lake.
Without getting into the nitty gritty, a temperature difference of at least 13° between that of the lake’s surface and about a mile up in the atmosphere.
So warmer lakes means there will be a bigger temperature difference between that of the air above and the lakes below.
What Causes Lake-Effect Snow
No not really. It’s actually a very complicated scientific process with loads of variables including temperatures, moisture in the air, wind shear, fetch, and instability.
But we can break it down to simply:
- Cold air blows over relatively warm water
- The air at the surface heats up and gathers moisture from interaction with the lake
- When that warm, moist air hits the colder landmass– the magic happens
- The warm, moist air is lighter than the cold, dry air at the surface
- The lighter air rises, and as it does so it condenses as it cools
- The moisture falls back out giving us those incredible snowfall totals
All along replenishing itself– hence the “lake-effect snow machine”
Major Differences in Accumulation
One of the most fascinating things about lake-effect snow is just how much the snowfall totals vary from one spot to another.
If you’ve ever tuned into WeatherNation for our coverage of one of these systems you have seen just this.
A field correspondent might be in one place and have snow coming down so hard visibility is almost zero, while just a few miles away hardly any snow falls at all.
This is because lake-effect snow sets up in bands.
There are once again countless factors that influence these bands and the places they setup, but as usual we can simply it for terms of explanation.
- Wind Direction
The bands setup down wind of the lakes. So each of the bands is oriented in the direction the wind is blowing.
The fetch is the distance the cold wind travels over the warm water. Different wind orientations give us different fetches.
The longer the fetch the more intense the band. A greater fetch means more individualized, long bands of snow; while a shorter fetch typically means more clustered, shorter and widespread bands of snow
There is a whole lot more science involved in all of this, so if you want a more detailed explanation feel free to find me on social media and ask any additional questions you might have!
For WeatherNation – Meteorologist Jeremy LaGoo