Why is the weather system of snowfall caused by the Great Lakes effect in the Great Lakes region of North America a warm front?

The Great Lakes effect refers to the phenomenon that cold air meets a large area of unfrozen water surface (usually a lake) and gains water vapor and heat energy from it, and then forms precipitation on the windward bank of the lake, usually in the form of snow. This situation is most famous for the snowfall along the Great Lakes in the northeastern United States. Other waters, such as some oceans and lakes, will also produce the Great Lakes effect, resulting in smaller snow belts. For example, in the snow belt on the east coast of the United States, the high pressure area centered on Quebec in winter makes the atmosphere flow clockwise, making the polar air mass reach the North American coast south through the Atlantic Ocean and pass through the warm water in the Gulf of Mexico, bringing snowfall to the east coast of the United States. Although snow is brought by the Atlantic Ocean instead of lakes, it is also called Great Lakes effect snowfall. The Great Salt Lake in Utah, Hudson Bay in Canada and St. Lawrence Bay will all produce the Great Lakes effect snowstorm.

cause

Take the Great Lakes region as an example. Autumn has come, and the Great Lakes are getting colder, but winter will not be completely frozen. In winter, the air mass mainly crosses North America from west to east. In summer, the land absorbs heat radiation, the continental air mass becomes very cold, and the polar air mass moves south to the mainland. When the air mass passes through the lake, the air with extremely low temperature contacts with the relatively warm water surface, the temperature at the lower part of the air mass rises, and water vapor enters the air mass. Now the lower part of the cold air mass is a warm and humid atmosphere. The cold and dense air mass sinks, which leads to the rise of warm air, the drop of temperature, the condensation of water vapor, the instability of air and the formation of clouds, usually stratocumulus, stratocumulus or cumulus. Generally speaking, when a cold air mass travels halfway over the Great Lakes, it will form a cloud and drift eastward with the airflow. Then the atmosphere came over the cold continent, and the contact with the ground slowed down the movement of the atmosphere. The atmosphere floating from the lake continued to gather along the coast, the warm air mass continued to rise, the clouds thickened, and precipitation began. Due to the low air temperature in the lower layer, water vapor falls in the form of snow.

Snowfall and location

The location of snowfall depends on the wind direction and speed of moving clouds. The wind speed determines the distance traveled by the snowstorm. The stronger the wind, the farther the water vapor is carried, and it spreads farthest in late autumn and early winter. The snowfall depends on the following factors: the temperature difference between the cold air mass and the water surface. When the temperature difference is large, the higher the water temperature, the lower the temperature of the cold air mass, the more water vapor condenses and the greater the snowfall. Generally, this temperature difference is easy to occur in June 5438+February and June 5438+ 10, and it is also the most prone to snowstorms. The distance that cold air travels on the water, that is, the blowing distance, will also affect the snowfall. The longer the cold air touches the warm water surface, the more water vapor the air mass carries. If the water freezes and the water vapor supply stops, the Great Lakes effect will stop.

Great Lakes Effect in the Great Lakes Region

200 1 Christmas Eve, a snowstorm hit New York State. By the end of the snowstorm on New Year's Day, the snow in Buffalo was 82.3 inches (2 meters) deep. This is indeed a devastating snowstorm, but it is not surprising. Buffalo people are used to snowstorms like winter snow and have attacked the city more than once. 1937 65438+February, in one day, the whole city was covered with snow as deep as 4 feet (1.2m).

On February 2, 2002, 65438, it was Eswell's turn in new york. Only one snowstorm has a snow depth of 26 inches (66 cm). In the winter of 2002~2003, the northern hemisphere was colder than before, especially the snowstorm. On June 65438+1October/kloc-0 ~12, the hourly snowfall in western New York was 4-5 inches (10~ 12.5 cm), and the snowfall in a county in southern Buffalo was 24 inches (6. A few days later, another snowstorm happened. In Oswego, 24 inches (665,438+0 cm) of snow fell in 9 hours, and Sirideng fell 40 inches (65,438+0 m). It often snows in Oswego.1From October 27th to 365, 438+0, 65, 438+0, 6966, the depth of snowstorm reached 8.5 feet (2.59 meters). Another snowstorm occurred in the winter of 1976~ 1977. In June+10/October, 5438, the snow in new york Hook reached 12.4 feet (3.78 meters). In the whole winter that year, the snow in Hook totaled 39 feet (1 1.86 meters). This depth can bury a two-story building. In some parts of Michigan, the snowfall in one winter is as deep as 33 feet (10 meter), and the average snow depth in the state is 16 feet (5 meters). Of course, the snowfall is not average every day, and a large part of it is produced during the snowstorm, especially when there is a snowstorm.

These areas are all in the eastern part of the Great Lakes, where heavy snowfall has a certain impact on the United States and Canada. From eastern Minnesota and Manitoba in the west to Pennsylvania, New York, eastern Ontario and Quebec in the east, the water vapor falling in the form of snow actually comes from the Great Lakes. There is a snow belt in this area, which extends from the lake to the downwind for 50 miles (80 kilometers). The snowfall in this area is much greater than that in other areas at the same latitude.

The Great Lakes Effect in Europe and Asia

Because of the Great Lakes effect, no continent can match the snow belt in eastern North America, because no continent has water in an excellent position like the Great Lakes. This is not to say that Europe and Asia do not have the Great Lakes effect. Every autumn, the temperature in Siberia drops and the cold air with high cold density sinks, resulting in a large area of cold high pressure. The atmosphere moves outward from the cold high pressure, through Lake Ladoga in Russia, and westward through the Gulf of Finland and the Baltic Sea. The cold atmosphere comes into contact with warm sea water to obtain water vapor. When it reached the east coast of Sweden, these humid and relatively warm atmospheres began to cool after crossing the coast, forming snowfall in the southeast of the country. Siberian cold air flows eastward, far away from the winter high pressure center, passing through Mongolian Plateau and Gobi Desert, bringing dry and cold weather to northern China. Cold air passes through the coast, gathering water vapor in the northern Sea of Japan. When it reached the west coast of Honshu and Hokkaido, Japan, the warm Kuroshio raised the temperature of seawater and made the atmosphere relatively humid and warm. When the atmosphere passed through the coast of Japan, it was forced to bypass the mountains and move along the west side of the coastal islands, and it began to snow. To the south, Siberian cold air passes through the Yellow Sea, gaining water vapor and gathering in the western part of the Korean Peninsula and the northern part of the Shandong Peninsula to form snowfall. Because the distance of cold air passing through the Yellow Sea is shorter than that of the Sea of Japan, its effect is relatively weak.

China's Great Lakes Effect

Blizzard in Weihai, Shandong Province on February 4th, 2005. In China, the Great Lakes effect snowfall is usually called cold current snowfall. Only a small part of the northern Shandong Peninsula in China will experience the Great Lakes snowfall, and the effect is weaker than the above places. The uplift of the hilly terrain of Shandong Peninsula will strengthen the snowfall in its northern coastal areas and even cause snowstorms. From February 4th, 65438 to February 4th, 2 1 year, Weihai, Yantai and other places in the northern part of Shandong Peninsula were hit by continuous snowstorms, among which Weihai suffered several blizzards, with total precipitation of nearly 100 mm and 49 cm of snow, which caused traffic paralysis.