Starting the Snow Machine!

Although it is still the Fall season, aside from the little refreshing warmth early this week, it has been quite cold! Saturday was especially bitterly cold! However, the cold temperatures we (in the Tri-State) felt the past few days is not even comparable to single digits felt in the Northern Plains.
This post was inspired by a gorgeous friend who was interested in the idea of lake-effect snow. Right around this time of year through January, lake-effect snow is a pretty hot topic for the Great Lakes and surrounding areas; so why not write about it!
The general notion of the weather that occurs at a given moment or time is due to fronts i.e. cold, warm, stationary and so on. Cold fronts are followed by cooler air (CAA: cold air advection or movement of air) then what was previous in place prior to the frontal passage and so on. However, what the general public do not take into consideration that the weather and weather forecasts are largely influenced by air masses. An air mass is an extremely large body (area) of air which the properties of temperature and moisture content (humidity) are similar in any horizontal direction at any altitude. This area that an air mass encompasses is not just a few kilometers. It is more like a few thousand kilometers. Not only is temperature an important component. The actual source region of the air mass is a very important characteristic. These regions are where the air masses originate. In order for a such a huge mass of air to develop and to form characteristics from the source region, the air mass must remain stagnant over the region for a long(ish) period of time and thus will acquire the properties from the surface below.
There is one more part to the puzzle before I get to the snow machine. When it comes to air masses, there is a classification. Like mentioned before, air masses are classified according to their temperatures and humidities. There are warm and cold air masses, we well as there are moist and dry air masses. The image below refers the the kinds of air masses, their source regions, and the characteristics.

North American Air Masses

Now that we have a little background information on air masses, the idea of lake-effect snow can be explained. With air masses and source regions in mind, when a cold, dry air mass moves over a relatively warm body of water (the Great Lakes), heavy snow showers can form, also known as lake-effect snow! From November through January when the weather in the Mid-west is more of less dominated by clear and cold cP (continental polar) air, locations on the eastern shores of the Great Lakes often experience snow, sometimes heavy in nature. These snow showers that form on the downwind side of one the the lakes is known as lake-effect snow. The snow could fall as showers to even heavy snow squalls. Depending on the wind flow direction, part of a city/town area could experience just simply clouds while the other side of town could have a few inches of snow on the ground! The image below depicts the formation of lake-effect snow. 

Lake-Effect Snow Courtesy of MetEd

Between November and January, cold air moves over the Great Lakes when they are still relatively warm and not quite so frozen. Some studies have actually noted that it is the contrast in temperatures between the water and air that is the potential for snow showers. This difference can be as great as 45 degrees F! Referring to above, when cold air moves over the warmer water, the air mass is quickly warmed from below making the air more buoyant and less stable. Over the water, the water the vapor condenses into fog steam, warming as it rises and form cumuliform clouds that continue to grow and before more unstable. In time, these clouds will produce snow showers. Right on the eastern shores of the Great Lakes is the most snow. However, here in Jersey we have seen a few lake-effect snow flurries, but will never receive much accumulation. Once the air and clouds reach the eastern shores, additional lifting of air is provided by low laying hills. The terrain and the convergence of air slows down the amount of snow accumulation and the snow eventually tapers off leaving trace amounts or low laying cumulus clouds drifting over head. Over the Winter season, as the lakes begin to freeze, lake-effect snow showers become more numerous because there is less of a temperature contrast between the surface and the air. Just a note: the longer the distance over which the air mass travels, the greater the amount of warmth and moisture is taken from the waters, and the greater the potential for heavy snow. This lake-effect snow can bury a city in a matter of few days! In just a few days in December 2001, Buffalo, NY received just about 7 feet of snow. Compare that to Montague, NY in January 1997 that received over 7 feet of snow in less than 48 hours!

Let the snow factory open shop!

~ V.S.