Warm Front - Characteristics

Characteristics

If the air mass is relatively stable, and the warm front is a katafront, rainfall will increase until the front reaches the location, at which time the clouds can extend all the way to the earth’s surface as fog. Once the front passes, the location experiences some warming and clearing. If the air mass is unstable, and the warm front is an anafront, thunderstorms may precede and follow the front and temperature changes will be larger.

In the northern hemisphere, a warm front causes a shift of wind blowing from southeast to southwest, and in the southern hemisphere a shift from winds blowing from northeast to northwest. Common characteristics associated with warm fronts include:

Weather phenomenon	Prior to the Passing of the Front	While the Front is Passing	After the Passing of the Front
Temperature	Cool	Warming suddenly	Warmer, then leveling off
Atmospheric pressure	Decreasing steadily	Leveling off	Slight rise followed by a decrease
Winds	South to southeast (Backing)(northern hemisphere) North to northeast (Veering)(southern hemisphere)	Variable	South to southwest (Veering)(northern hemisphere) North to northwest (Backing)(southern hemisphere)
Precipitation	Showers, snow, sleet, or drizzle	Light drizzle	Usually none, sometimes light rain or showers
Clouds	Cirrus, cirrostratus, altostratus, nimbostratus, then stratus (pilots use the acronym CCANS) and fog; occasionally cumulonimbus in summer. Other clouds can also often be seen including cirrocumulus amongst the approaching cirrus, the altostratus becoming broken in places into altocumulus (particularly if the front is weak) and the very common occurrences of stratocumulus under the cirrostratus and altostratus and stratus fractus under the nimbostratus.	Stratus, sometimes cumulonimbus	Clearing with scattered stratus and stratocumulus. If the warm front is part of a depression, there is often a sheet of altostratus (often broken in places to altocumulus) above this which thickens when the cold front approaches.
Visibility	Poor	Poor, but improving	Fair in haze
Dew Point	Steady rise	Steady	Rise, then steady