STRATUS CLOUDS

These clouds are flat (look like sheets). Their ascending motion of air is weak relative to cumulus clouds. Stratus clouds tend to extend over large areas (sometimes covering the entire sky) and durations to produce widespread rain and snow => This is because dynamic lifting tends to occur over a large region while convective lifting tends to be more focused over a smaller area.

The two ingredients that form stratus cloud include dynamic lifting (rather than convective lifting) and air with a high enough relative humidity that it can be saturated upon lifting. Dynamic lifting is a slow lifting => this is why stratus clouds are flat looking, instead of vertically developed like cumulus clouds are from convective lifting. The relative humidity will vary with height and regions of lifting (if present) will vary with height. The best combination of high relative humidity and lifting or where lifting is first able to saturate the air is where stratus clouds will first form.

• Dynamic lifting occurs from large synoptic scale lifting mechanisms such as fronts, low pressure convergence, low level warm air advection, positive vorticity advection and jet stream divergence.