The last few days have had us living in the land of Alberta Clippers. Several in rapid succession have given us lovely new layers of fresh fluffy snow. We are in the midst of another one right now- and this one is giving us a bit more snow than usual because it is complemented by moisture laden air from the south heading our way. Those of us living in Duluth and along the North Shore are currently under a Lake Effect Snow Advisory. Fun, because living on the western and southern end of the lake we don’t get Lake Effect Snowfalls very often, unlike those who live to the east of us along the shore of Lake Superior.
So what’s all this stuff about Clippers and Lake Effect? Most of us are familiar with the terms but may not understand why they happen or don’t happen! Let’s start with the idea of an Alberta Clipper- which by the way can also be called a Manitoba Mauler, or Saskatchewan Screamer, depending on the Province it originated in. They are all the same thing- fast moving low pressure systems blowing cold air in from the arctic and originating somewhere in the prairie Provinces east of the Canadian Rockies. Ordinarily they usually bring heavy wind, lots of cold, and generally little snow. This is largely because cold air can’t hold as much moisture as warmer air, and traveling over the prairie doesn’t provide anywhere to pick up any additional moisture. That is, until you hit the Great Lakes, or in this case have another system blowing warmer wetter air from the south, then Lake Effect Snow steps in for our region.
Lake effect snow happens when cold dry air travels over open water, which is warmer in the winter than the cold air over the land. Lake Superior is very large, being roughly 350 miles across east to west and another 170 or so miles from north to south. It is a comparatively rare event for the lake to freeze over entirely, and this is an event that is becoming rarer and rarer. But I digress- that is a topic for another day! Unfrozen water provides warmer air near the surface of the lake. As cold air from the land travels over long stretches of unfrozen water, a storm can pick up a lot of moisture. But when the storm reaches land again, it once again hits colder air, and as the air cools it can’t hold the amount of water it held over the warmer water, so it has to dump it as snow. In order to have Lake Effect Snow, the storm system generally needs to travel over at least 100km or about 62 miles, of unfrozen water, easily done on Lake Superior! The wind needs to be the right speed, slow enough to pick up moisture, but fast enough to keep the system moving. Ideal wind conditions seem to range somewhere between 10 and 40 mph. Prevailing weather patterns generally move low pressure systems from the west towards the east, so the western side of the lake generally doesn’t see as much lake effect snow as the eastern side of the lake. The infamous lake effect locations usually are east of large stretches of water, as depicted in this SeaGrant image.
Figure 1 (http://www.seagrant.umn.edu/superior/processes)
In the image above you can see that snow is not the only precipitation that is greater in these areas, rainfall is also higher in these areas as well.
So how come the Lake Effect Snow advisory was issued for Duluth area and the north shore? We only get the Lake Effect when we have consistent winds from the east or northeast for extended periods of time. This storm gave us that rare opportunity to have some Lake Effect Snow. The winds have been blowing from the east or northeast for more than 24 hours now, plenty long enough for the cold air to pick up moisture from the lake and give it to us as the air hits the colder air on land! Hooray for Lake Effect!
Another interesting factor in play here is elevation. When air comes off the lake and hits hills the air is forced to go up and cool along the way and leave the moisture behind. Those of us who live in Duluth are well familiar with it snowing up the hill and doing nothing downtown. The same can be said all along the North Shore. More snow is typically inland from the lake. For example downtown Duluth averages about 55 inches of snow a year, while up at the Duluth airport the average is 79 inches of snow per year. That’s a difference of 24 inches, and all thanks to a rise of about 800 feet! Well, will leave you all to go enjoy some of the snow- who knows what will arrive this weekend- could be more snow, or more of the freezy icky stuff. I’m personally hoping for snow! Til next week!
These updates are made possible by a generous donation from David and Rosemary Good.