The range of altitudes within which the lifting condensation level (LCL) occurs for different air parcels rising from near the surface. Due to natural variability and land-use heterogeneity, air parcels at different horizontal locations near the ground usually have slightly different temperatures and humidities. As a result, each air parcel has its own LCL. Over a town, for example, LCLs might vary from 1000 m over an irrigated park to 1400 m over a paved parking area, thus giving a 400 m thick LCL zone centered at 1200 m. This implies that cumulus clouds formed from rising surface-layer air will have slightly different cloud-base altitudes within a region. While it is difficult to see this effect when observed from the ground, it is very obvious to aircraft flying at the average cloud-base altitude.