What type of cloud is this? Low 'fair weather' cumulus cloud (Cu) type 1 and type 2. There is also some patches of dense cirrus (Ci type 2) above. The cumulus are dry in this instance, though Cu 2 can produce some precipitation (shower) activity. The official description is 'Puffy, woolly detached clouds of varying density and generally with sharp outlines'. Developing vertically in a cauliflower shape, but only to a limited extent. White sunlit sections; the bases are darker and nearly always horizontal. At the end of their short life they become torn by the wind, often appearing to change colour from white to perhaps a dull grey. Mostly composed of liquid droplets, ice particles possible in cold temperatures
What does it tell you about the present weather? No significant present weather. The cloud elements result from vertical currents or thermals of moist air rising from a warm surface - a `relatively' stable atmosphere limiting the cloud from developing further. Since most Cu are found below 5000 feet, their movement can be taken as closely representing the airflow around the isobars - the gradient wind
What about the future weather and for how long? Most frequent over the land in the afternoons and the sea when the temperature of the air is less than the sea surface temperature (SST). Increased vertical development of the cloud is a certain sign of increasing instability and the possibility of showers. Clouds at the `wrong' time of the day indicate other lifting mechanisms or increased instability.
What influence will this cloud have on the surface winds? Dry cumulus clouds generally suck from bases, while wet ones blow air out from their bases - however, it is possible for a cumulus that appears to be dry to behave as a 'wet one'. As a general rule, the dry ones have less impact on the surface winds; the base of the cumulus cloud needs to be below 2000 ft to influence the surface winds, or the depth (thickness) of the cloud needs to be greater than its height above the surface.
For a complete set of detailed cloud notes contact Marine Weather Services, clouds@ozemail.com.au