Snow can also form from very cold air flowing over a large ice-free lake, a situation called lake effect snow. In mountainous regions, air being forced to rise as it flows up and over the mountain can cause large snowfall accumulations. Precipitation caused by this mountain-forced ascent is called orographic precipitation.
Snow clouds usually occur in the context of larger weather systems, the most important of which is the low pressure area, which typically incorporate warm and cold fronts as part of their circulation. Two additional and locally productive sources of snow are lake-effect (also sea-effect) storms and elevation effects, especially in mountains.
Snow occurs when water droplets in clouds freeze, and these droplets then act as a nucleus onto which molecules of water vapor adhere, forming larger ice crystals. Once the growing snowflake is too heavy for the movement of air in the clouds to support, it falls to the ground.
In February 2007 some portions of Oswego County, New York received up to 11 feet of snow in a 5 day time frame. also the lake effect can make tremendous snow in the winter. it may cause lots of ...
Thundersnow is a snowstorm event in which thunder and lightning occur. An example is the classic 2011 thundersnow in Chicago that surprised Jim Cantore. Thunderstorms accompanied by snow are ...
What causes snow storms? Snow storms are usually caused by rising moist air within an extratropical cyclone (low pressure area. The cyclone forces a relatively warm, moist air mass up and over a cold air mass. If the air near the surface is not sufficiently cold over a deep enough layer, the snow will fall as rain instead.
Narrow bands of snow can occur anywhere in the United States. An excellent example of a narrow snowband occurred on November 20, 2015. Below is a plot of the snowfall across southeastern South Dakota and northern Iowa. Notice the large difference (or gradient) in snowfall from south of Interstate 90 ...
Lake-effect snow contributes to approximately 6–8 snowfalls per year in Salt Lake City, with approximately 10% of the city's precipitation being contributed by the phenomenon. Similar snowfall can occur near large inland bays, where it is known as bay-effect snow.
As a general rule, though, snow will not form if the ground temperature is at least 5 degrees Celsius (41 degrees Fahrenheit). While it can be too warm to snow, it cannot be too cold to snow. Snow can occur even at incredibly low temperatures as long as there is some source of moisture and some way to lift or cool the air.
Both freezing rain and sleet occur by the same general process: liquid raindrops in a layer of warm air well above the surface fall into a layer of freezing air hugging the ground. The difference between these two wintry precipitation types depends on the thickness of the layer of freezing air ...