Initiation of convective cells in relation to water vapour boundaries in satellite images

Strong convection and severe thunderstorms can be observed within specific synoptic situations: on the one hand associated with fronts or frontal zones, on the other hand under “fair-weather” conditions. Comprehensive observations of satellite images and sequences show that the first appearance of deep convection under “fair-weather” conditions can be associated to the transition zone between relatively high pixel values and relatively low pixel values in the WV satellite imagery. This boundary represents not only the transition between relatively humid and dry air at levels above 600 hPa but also has typical characteristics in other parameters and/or processes which favour the growth of convective cells. The fact of the first appearance of deep moist convection at brightness boundaries in the WV imagery can be used for regional Nowcasting.