Milwaukee – Cold air, significant cold air, is finally forecast to arrive for most of the northern United States in the days leading up to Thanksgiving. Our very warm Fall has meant little snow and even less Lake Effect Snow. We talked about this last week, when we published an article on the end of the mild fall weather. As stated in that article, the mild weather has been shared with many of Canada’s cities.
The second half of November still shows the likelihood of colder temperatures – most likely a drop to normal levels and possibly below normal. By late November, that is cold enough for Lake Effect Snow. Do you live around the Great Lakes or know somebody that does? If they live on the leeward – south or east side of a Great Lake, they can get serious, monstrous snowfall. Just two years ago, November 2014, New York was hit with two big Lake Effect Snow events. Fig. 1 is a map of the first event that lasted from November 17th through 19th.
Fig. 1 Western New York LES Event
That bright bulls eye is just south of Buffalo, New York. South Cheektowaga was the epicenter with 66” of snow. Unbelievable! Now, I am showing you this because prodigious amounts of snow are possible in November and early December around the Great Lakes not because a comparable event is likely in ten to fifteen days. So, why does Lake Effect Snow occur and why are some events more significant than others?
Unique Geography Affecting Lake Effect Snow
Let’s start with the base. This can only happen in a few locations in the world. You need open water on large lakes or oceans and you need incursions of very cold air – arctic air that is well below freezing. If you look at a world map, there are no locations in the southern hemisphere that qualify. In the northern hemisphere, North America has the Great Lakes and many Canadian lakes – Great Bear Lake, Great Slave Lake and Lake Winnipeg. In the United States, in addition to the Great Lakes, Lake Effect Snow has occurred on Great Salt Lake, Lake Champlain and even some of the bays along the east coast. In Europe and Asia, Lake Effect Snow has occurred over the Baltic Sea, Black Sea, Caspian Sea, Sea of Japan and Lake Baikal. However, most of these locations either are too far north and ice over for most of the season or are too far south and have very infrequent incursions of arctic air. Guess where in the world the lakes stay mostly, at least partially, ice free in winter and have frequent incursions of cold air? You only get one guess. Yes, the Great Lakes are very unique for fresh water and weather. There is no other location in the world that combines water, cold and prodigious snowfall, outside of mountains, like the Great Lakes. So, the first three ingredients are unique geography, large open water and frequent incursions of arctic air.
Temperatures and Lake Effect Snow
Now, we can dig a little deeper. Let’s talk about temperatures. In a Lake Effect Snow Event, there are two critical temperatures – the arctic air mass and the water temperature. The greater the difference between the arctic air mass at about 4,000 feet and the surface water, the more energy is transferred from the water into the atmosphere. This occurs through evaporation of water from the lake and condensation into the cloud; the greater the transfer, the more significant the snow event. The greatest temperature difference is most likely in late Fall and early Winter, when lake water can still be in the 40s and 50s. Arctic air masses can be as cold as 0° to 10° degrees – a 40 to 50 degree difference. An atmosphere with such a change in temperature vertically is also called unstable or convectively productive. The air just above the water climbs very quickly when temperatures at 4,000 feet are much colder. This creates an even greater exchange of energy and moisture. Figure 2 shows the process of transferring water from the lake into the cloud and then onto the land through snow.
Fig. 2 Basic Lake Effect System
Winds Influence Lake Effect Snow
A second and very important step is the wind field from the top of the cloud down to the surface. The wind direction needs to be uniform. If the wind shifts significantly within the cloud, the snowflake process is disrupted. This results in cloudy skies and flurries – not significant snow. How the wind aligns with long axis of any of the lakes is also very important. Let me explain why. If the wind aligns with the long axis of the lake, more moisture is transferred from the lake into the cloud. In fact, for Lake Effect to be possible, a fetch of more than 60 miles is needed. Any distance shorter, results in clouds and flurries. If you look at figure 3, you can see that the most significant snowbelts are located at the end of the long axis of each lake – for example, northwest Indiana, western New York.
Fig. 3 Lake Effect Snowbelts
Not only are the most significant snowbelts located at the end of the long axis, but they also benefit from moisture from multiple lakes. If you live in Muskegon or South Bend, many of your Lake Effect Snow events gather moisture from Lake Michigan and Lake Superior. In Cleveland and Erie, you receive moisture from Lake Huron and Lake Erie. In Syracuse and Watertown, your Lake Effect Events can tap into moisture from Lake Superior, Lake Huron and Lake Ontario. If you live in southern Ontario, your snowflakes can originate from moisture gathered from Lake Superior and Lake Huron.
Topography Affects Lake Effect Snow
One last point to make about Lake Effect Snow: A significant increase in elevation in a snowbelt, enhances or increases the potential for snowfall. This is most notable in the Upper Peninsula of Michigan and the Tug Hill Plateau of New York. These two locations, by far, receive the greatest annual Lake Effect snowfall. Hooker, New York holds the state record of 467” of snow and Hancock, Michigan holds the state record of 390” of snow. You can see these two bulls-eyes in the annual snowfall of the western and eastern Great Lakes found in figures 4 and 5.
Fig. 4 Western Great Lakes Annual Snowfall
Fig. 5 Eastern Great Lakes Annual Snowfall
As winter progresses, the water temperature cools and ice begins to form on the Great Lakes. This reduces the potential for Lake Effect Snow by February and March. Coinciding with the late season ice formation is Spring. The warmer season means fewer incursions of Arctic air.
So, what are some of the biggest snows? They happen from very cold air, warm waters, uniform wind direction and in locations with significant elevation. Christopher Burt, writes for the Weather Underground, and has researched these impressive Lake Effect records:
||Amount of Snow
||Benetts Bridge, NY
And now that we are in the social media and digital age, we can see pictures like these:
Fig. 6 Photo: AP
Fig. 7 Photo: Cheryl Boughton
Fig.8 Photo: Michael Garood
What to Do
Hopefully, you understand some of the fundamentals of Lake Effect snow and why this is such a unique characteristic in the world. You should also now be aware that we are in Lake Effect Snow season. We have had a very warm Fall. The outlook for late November still shows colder air moving into southern Canada and the northern United States. It is now likely that the first significant Lake Effect Snow of the season comes during the week of Thanksgiving. Can you hear me Marquette, Muskegon, southern Ontario, Cleveland, Erie, Buffalo and Syracuse? If you live around the Great Lakes, you should finish prepping for winter. Again, it looks like it changes quickly in the next week to two weeks.
Meteorologist Mark McGinnis is on Facebook, LinkedIn and Twitter @fairskiesconsul