Warm Sector

The warm sector of a mid-latitude cyclone is defined by the American Meteorological Society as follows:

That area, within the circulation of a wave cyclone, where the warm air is found.  Traditionally, it lies between the cold front and warm front of the storm; in the typical case, the warm sector continually diminishes in size and ultimately disappears (at the surface) as the result of occlusion.

Simply put, when a warm front lifts to your north, and a cold front is present somewhere to the west, you are in the warm sector of the system.  Typically, winds will shift from the south within, allowing for warm, moist air to advect into the given location.

This particular setup has been known to supply the fuel needed to produce convection, as the trailing cold front serves as a forcing mechanism to lift the warm, moist air vertically into the atmosphere.