Longman Dictionary of Contemporary English
Wiktionary
n. (context meteorology English) A warm front is the trailing edge of a retreating mass of cold air.
WordNet
n. the front of an advancing mass of warmer air
Wikipedia
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fronts, and move more slowly than the cold fronts which usually follow because cold air is denser and less easy to remove from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly stratiform, and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.
Usage examples of "warm front".
A hint of a warm front blowing in from the east clouded the exhalation of fire that had teased her.
It was a wild, ugly night, the air much warmer so that I thought I could smell rain again, the warm front moving in.
We settle down to watch him, wrapping tail around to warm front feet.
It was starting to rain, one of the icy rains that passed for a warm front in beautiful Hakazit, but in this case he didn't mind since it had pretty well cleared the streets of general traffic.
The sensations reminded him, oddly, of colliding air masses, which boiled up into storm fronts before mixing into something that was neither a cold front nor a warm front, neither high pressure nor low, a hybrid sort of weather that was wildly unpredictable.