Cold fronts move at speeds from 10 to 50 knots. In winter they are 2 or 3 times faster than in the summer. A fast-moving cold front may be preceded by a squall line, a roll of black, threatening clouds with violent storms. Wind shifts suddenly along the front, and wind velocities increase dramatically. Behind the squall line are heavy rains, then clearing, and gusty winds, usually followed by several days of clear, cool weather.
Warm fronts are quite different.
The high, thin cirrus clouds that form when the warm air climbs up and over the retreating cold air mass can extend as far as 1,000 miles ahead of the front. These clouds thicken and lower as the front advances, and winds increase steadily. As the clouds lower, rain or snow begins to fall, continuing until after the front passes. The winds shift clockwise and decrease. The temperature begins to rise and visibility becomes poor.