Plain English Meaning

A weather boundary where warm air is moving in and pushing cooler air out. Because the warm air rides up over the cooler air gradually, you usually get a long stretch of low clouds, steady rain or drizzle, and poor visibility before the front actually passes.

Full Definition

The boundary along which a mass of warm air is advancing and replacing a retreating mass of colder air. The warm air, being less dense, slides up and over the colder air, producing a long, gently sloping frontal surface. This typically results in a wide band of stratiform clouds, steady precipitation, lowered ceilings, and reduced visibility well ahead of the surface position of the front.