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. A 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 . The leading edge of an advancing cold air mass that displaces warm air in its path is called a cold front.