Warm Front
transition zone from cold air to warm air

A warm front is defined as the transition zone where a warm air mass is replacing a cold air mass. Warm fronts generally move from southwest to northeast and the air behind a warm front is warmer and more moist than the air ahead of it. When a warm front passes through, the air becomes noticeably warmer and more humid than it was before.

Symbolically, a warm front is represented by a solid line with semicircles pointing towards the colder air and in the direction of movement. On colored weather maps, a warm front is drawn with a solid red line.

There is typically a noticeable temperature change from one side of the warm front to the other. In the map of surface temperatures below, the station north of the front reported a temperature of 53 degrees Fahrenheit while a short distance behind the front, the temperature increased to 71 degrees. An abrupt temperature change over a short distance is a good indication that a front is located somewhere in between.

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

Before Passing While Passing After Passing
Winds south-southeast variable south-southwest
Temperature cool-cold, slow warming steady rise warmer, then steady
Pressure usually falling leveling off slight rise, followed by fall
Clouds in this order: Ci, Cs, As, Ns, St, and fog; occasionally Cb in summer stratus-type clearing with scattered Sc; occasionally Cb in summer
Precipitation light-to-moderate rain, snow, sleet, or drizzle drizzle or none usually none, sometimes light rain or showers
Visibility poor poor, but improving fair in haze
Dew Point steady rise steady rise, then steady
Table adapted from: Ahrens, (1994)

Cold Front
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