Winter Storm Development
Winter storms have various components, including low pressure centers, warm fronts, and cold fronts. In the continental United States, winter storms are common from November through April, and sometimes as early as October or as late as May.
The winter dip in the jet stream allows polar air to surge south. This cold, dry air brings with it temperatures cold enough for snow, sleet, or freezing rain to develop.
Warm tropical air filled with moisture from the Gulf of Mexico often continues to flow up from the south during the winter months. When this warm, moist air mass from the south meets the cold, dry air mass from the north, they can create winter storms.
Low Pressure SystemsThe term low pressure is used to indicate an area of air pressure that is lower than other areas of pressure around it. Air always moves from areas of high pressure to areas of low pressure.
If not for the coriolis force, winds would blow in a straight line. The earth's rotation causes winds to turn as they move away from high pressure areas into areas of low pressure. In the Northern Hemisphere, these winds circulate counterclockwise around areas of low pressure or cyclones.
As the low develops, the warmer air from the south begins to flow northward on the eastern side of the low. At the same time, colder air from the north flows southward around the low's west side.
Areas of low pressure which produce winter storms often form along a developing or pre-existing frontal boundary. When conditions throughout the troposphere are right, an intense winter storm may form.
Wintertime Warm FrontsA warm front does not have to wedge and push its way into a colder air mass. Warm air is both lighter and less dense than cold air. Because it is lighter, warm air merely lifts over the cold air it encounters.
The leading edge of a warm air mass encountering a retreating cold air mass is a warm front. As a warm front approaches, the clouds become thicker and lower in the sky. These clouds produce a variety of precipitation types.
Wintertime Cold FrontsThe leading edge of an advancing cold air mass that displaces warm air in its path is called a cold front. Because cold air is heavier and more dense than warm air, an advancing cold front must wedge its way under a warm air mass, then lift and push it out of the way.
Gusty winds and a sharp drop in temperature often accompany and follow cold fronts in the winter.