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General cloud explanation

This page is meant to provide very general information from experience about the formation of clouds in a Maltese context. Detailed official information can be found freely on many websites on the Internet.

High-level clouds (Cirrus [Ci], Cirrocumulus [Cc] and Cirrostratus [Cs]):

This refer to clouds that form at an altitude of between 6km and 13.7km above sea-level. In Summer and Autumn, these clouds are generally the result of leftovers from cumulonimbus clouds either locally or from nearby countries (Sicily or Tunisia). Cirrus and Cirrocumulus clouds tend to form when there is a certain amount of wind shear hence turbulence and when the upper-air is moist and unstable. Stratified high clouds (Cirrostratus) generally form before the approach of a warm front or sometimes at the edge of an arriving low pressure system. In fact, halos around the sun or the moon are due to these clouds when they are very thin. They also form under high pressure systems in quiescent conditions when the air above 6km is so moisturized that ice fog forms at that level. This is especially enhanced if some dust is present or an aeroplane happens to pass by.

Mid-level clouds (Altocumulus [Ac], Altostratus [As] and Asperatus [if classified]):

This refer to clouds that form at altitudes of between 2km and 6km above sea-level. Basically, the same mechanisms that form cumulus and stratus at lower levels apply except that the surface air may be cut off (through convectibe inhibition) from the formation of such clouds and that they are found at higher altitudes. In fact, most of the very rare thunderstoms that occur between May and July are generated from Altocumulus Castellanus and generally bring little to no precipation over the area since most of their rainfall would have dried out in the arid conditions present at that time of year.

Low-level clouds (Cumulus [Cu], Stratocumulus [Sc], Nimbostratus [Ns] and Stratus [St]):

This refer to clouds that are mostly confined to altitudes of below 2km above sea-level including fog which is simply defined as a stratus cloud on the ground. The exception is nimbostratus which can be found up to 3.1km above sea level. In Summer, cumulus clouds tend to develop on land due to prevailing winds encountering sea breezes and aided by the hot ground but inhibited by the upper-level Azores high pressure cell (which is why Summer thunderstorms are rare). During the rest of the year, these are developed due to instability (cumulus congestus eventually growing into cumulonimbus) and also by rising air thermals when the air is heated from below but encounters stable layers such as in the case of humilis and fractus. In fact, the latter 2 sub-species are known as fair-weather cumulus.
Stratified clouds (stratus and fog) in Malta are generally limited to the night and early morning hours. This is so because the sun's strength tend to burn these clouds off quickly (even in Winter) and sometimes even breaks any arriving nimbostratus into isolated showers. In addition, any arriving low pressure system in Winter encounters the still warmer sea. This increases atmospheric instability over the area resulting in the formation of cumuliform clouds rather than nimbostratus. Hence, nimbostratus clouds (producing incessant rainfall) persisting for long hours are relatively rare over Malta and when they do form, it's generally due to Easterly gales in Winter whereby moist-laden air from the sea allow condensation to steadily occur in slowly rising air. Stratus clouds may sometimes form locally over the Western side of Malta given very moist Westerly winds due to Malta's topography (The Western side of Malta consist of steep coastal cliffs rising up to 230 metres above sea-level) enhancing condensation.

All-level clouds (Cumulonimbus [Cb]):

This refers specifically to Cb clouds which can grow up to all levels of the atmosphere. In fact, a Cb can be up to 12km high! Sometimes, such cloud can totally darken the normally blue Maltese skies making it look pitch black as if it is night. However, it normally only lasts for a couple of hours.
In Malta, cumulonimbus clouds are most common during late Summer and Autumn when cooler air masses dragged by low pressure systems from Europe and the Atlantic make their way into the Mediterranean whereby they contrast with the warm, moist air and warm surface temperatures still present over the region. In fact, land and sea temperatures are at their warmest during late Summer. The sea temperature around Malta normally reaches 26°C by late August before beginning to cool. Such meteorological situation generate lots of instability (sometimes Convective Available Potential Energy (CAPE) of up to 2500J/kg) resulting in heavy convective storms. In Winter, these clouds are usually less severe and produce less precipitation. Of note is that most of the precipitation that falls in Malta comes from Cumulonimbus and Cumulus Congestus (also known as "Towering cumulus") clouds.

Cumulus and Stratocumulus clouds are the most common cloud types in the Maltese Islands.

Note: The information provided here is intended to acquaint the visitor with basic cloud terminology in relation with the Maltese prevalent weather conditions in order to be better able to understand and appreciate my website! This is certainly not intended to replace the expert descriptions and definitions provided from official sources!