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Cold Front
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  lower dew points

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Cold Front
transition zone from warm air to cold air

A cold front is defined as the transition zone where a cold air mass is replacing a warmer air mass. Cold fronts generally move from northwest to southeast. The air behind a cold front is noticeably colder and drier than the air ahead of it. When a cold front passes through, temperatures can drop more than 15 degrees within the first hour.

Symbolically, a cold front is represented by a solid line with triangles along the front pointing towards the warmer air and in the direction of movement. On colored weather maps, a cold front is drawn with a solid blue line.

There is typically a noticeable temperature change from one side of a cold front to the other. In the map of surface temperatures below, the station east of the front reported a temperature of 55 degrees Fahrenheit while a short distance behind the front, the temperature decreased to 38 degrees. An abrupt temperature change over a short distance is a good indicator that a front is located somewhere in between.

If colder air is replacing warmer air, then the front should be analyzed as a cold front. On the other hand, if warmer air is replacing cold air, then the front should be analyzed as a warm front. Common characteristics associated with cold fronts have been listed in the table below.

Before Passing While Passing After Passing
Winds south-southwest gusty; shifting west-northwest
Temperature warm sudden drop steadily dropping
Pressure falling steadily minimum, then sharp rise rising steadily
Clouds increasing: Ci, Cs and Cb Cb Cu
Precipitation short period of showers heavy rains, sometimes with hail, thunder and lightning showers then clearing
Visibility fair to poor in haze poor, followed by improving good, except in showers
Dew Point high; remains steady sharp drop lowering
Table adapted from: Ahrens, (1994)

Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

wind shift