WINTER STORMS NOR’EASTER Winter Storms How do winter storms form? Winter storms derive their energy from the clash of two air masses of different temperatures and moisture levels. Winter storms usually form when an air mass of cold, dry, Canadian air moves south and interacts with a warm, moist air mass moving north from the Gulf of Mexico. The point where these two air masses meet is called a front. If cold air advances and pushes away the warm air, it forms a cold front. When warm air advances, it rides up over the denser, cold air mass to form a warm front. If neither air mass advances, it forms a stationary front. How is snow formed? Snow is commonly formed when water vapor undergoes deposition, which is when water vapor changes directly to ice without first becoming a liquid, high in the atmosphere at a temperature of less than 32°F and then falls to the ground. How do blizzards form? A blizzard is a long-lasting snowstorm with very strong winds and intense snowfall. You need three things to have a blizzard; cold air at the surface, lots of moisture, and lift. Warm air must rise over cold air. What are snowflakes? Snowflakes are made of ice crystals. Each snowflake is six-sided and made of as many as 200 ice crystals. Snowflakes form in clouds where the temperature is below freezing. The ice crystals form around tiny bits of dirt that has been carried up into the atmosphere by the wind. As the snow crystals grow, they become heavier and fall toward the ground. Why is snow white? Bright snow blinds us with its gleaming white color because it reflects beams of white light. Instead of absorbing light, snow's complex structure prevents the light from shining through its lattice formation. A beam of white sunlight entering a snow bank is so quickly scattered by a zillion ice crystals and air pockets that most of the light comes bouncing right back out of the snow bank. What little sunlight is absorbed by snow is absorbed equally over the wavelengths of visible light thus giving snow its white appearance. So while many natural objects get their blue, red, and yellow colors from absorbing light, snow is stuck with its white color because it reflects light. What is sleet? Sleet is just rain drops that freeze into ice pellets before reaching the ground. Sleet usually bounces when hitting a surface and does not stick to objects. However, it can accumulate like snow and cause a hazard to motorists. What is freezing rain? Freezing rain is just rain that falls onto a surface with a temperature below freezing. This causes it to freeze to surfaces, such as trees, cars, and roads, forming a coating or glaze of ice. Even small accumulations of ice can cause a significant hazard. What is an ice storm? An ice storm is a type of winter storm caused by freezing rain. The U.S. National Weather Service defines an ice storm as a storm which results in the accumulation of at least 0.25-inch of ice on exposed surfaces. How do ice storms form? Ice storms form when a layer of warm air is between two layers of cold air. Frozen precipitation melts while falling into the warm air layer, and then proceeds to refreeze in the cold layer above the ground. This creates freezing rain or a glaze of ice. What is frost? Frost is white ice crystals that form on a surface, like the ground or leaves of a plant. Frost is created when the air temperature drops below freezing and the water vapor in the air freezes into ice crystals. How is lake-effect snow formed? As the cold air flows over the warm lake water, the relatively warm water heats the air's bottom layer as lake moisture evaporates into the cold air. Since warm air is lighter or less dense than cold air, the heated air rises and begins to cool. As the air cools, the moisture that evaporated into it condenses and forms clouds and snow begins falling from the cloud if the air is humid enough. (Graphic Credit: USA TODAY.) Warm moist air rises Cold air moves over warm water and is downwind of lakes and forms heavy warmed from below. Moisture evaporates in the air. snow. What is a Nor'easter? Nor'easters can occur in the eastern United States any time between October and April, when moisture and cold air are plentiful. A Nor'easter is named for the winds that blow in from the northeast and drive the storm up the east coast along the Gulf Stream, a band of warm water that lies off the Atlantic coast. They are known for dumping heavy amounts of rain and snow, producing hurricane-force winds, and creating high surfs that cause severe beach erosion and coastal flooding. 1. Nor’easter a) Nor’easters occur in the eastern United States between October and April, when there is more moisture in the air and it is colder. b) They are named for the winds that come in from the northeast and bring the storm up the east coast along the Gulf Stream (a current of warm water that moves northward up the Atlantic coast) c) They can produce heavy amounts of rain and snow. Hurricane- force winds can develop which can cause high surfs that lead to beach erosion and coastal flooding. 2. Two main components of a Nor’easter a) Gulf Stream low-pressure system. 1. Counter-clockwise winds. 2. These form off the coast of Florida, the Gulf Stream warms and brings about a low-pressure system, which circulates off the southeastern U.S. coast. This causes warm air to gather along with moisture from the Atlantic. Strong northeasterly winds at the edge of the storm bring it up the east coast. b) Arctic high-pressure system. 1. Clockwise winds. 2. While the strong northeasterly winds pull the storm up the east coast, it meets with Arctic air blowing down from Canada. When the two systems meet, it produces a mix of precipitation. 3. Two types of Nor’easters a) Offshore forming. b) Onshore forming. 4. High Pressure System a) Air slowly sinks, preventing clouds from forming, which is why highs are usually clear. b) High pressure usually brings about clear weather days. c) Is larger and moves slower than low pressure systems. d) Move clockwise. 5. Low Pressure System a) Air rises. b) As air rises, it cools, if there is enough water vapor, this will cause clouds and rain to form. 6. Hurricanes a) Large tropical storms with heavy winds in excess of 74 MPH. b) The ocean temperature has to be above 79 degrees F for a hurricane to develop. c) Has a peaceful center called the eye, which is normally 10-30 miles wide and contains calm winds, warm temperatures and clear skies. 7. Coriolis Effect a) The acceleration of a moving body on or near the Earth as a result of the Earth’s rotation. b) Alters the paths of projectiles (airplanes to boats to bowling balls) on Earth. 8. Trade winds 9. Doldrums a) Also called Equatorial Belt of Calms. b) Hurricanes can start in this area. c) The doldrums are also noted for calm periods when the winds disappear and can trap sailing vessels for long periods of time. 10.Sea States a) Sea States describe and categorized wave height in the ocean developed by the wind within a particular area. b) The height of the waves depends on how long the wind has been blowing in a certain direction, the distance the waves have traveled, currents and strength of the wind. They are measured within the limits set by the Beaufort Scale from 0 to 9. 11.Swells a) Strong winds from weather and storms blow on the surface of the water, creating ocean swells. b) The swells can travel long distances until they strike the shallow coastline and become strong, breaking waves. What is an Alberta Clipper? An Alberta clipper is an area of low pressure that generally forms over Alberta, Canada, east of the Rocky Mountains. They develop east of the Rockies because air flowing eastward over the mountains creates favorable conditions. Once an Alberta Clipper forms it usually moves very rapidly to the southeast across the USA's northern Plains and then to the east off the mid-Atlantic Coast. Clippers usually cause only light precipitation with very few producing major snowstorms. However, if conditions are favorable, some Alberta clippers can rapidly intensify off the East Coast once the storm taps the relatively warm moist air over the Atlantic Ocean. The storms that rapidly intensify sometimes spread heavy snow over New England and southeastern Canada. Generally, the main weather features associated with Alberta clippers are some light snow and a reinforcement of cold air over the USA. What is Wind Chill? The wind chill is the temperature your body feels when the air temperature is combined with the wind speed. The higher the wind speed the faster exposed areas of your body lose heat and the colder you feel.