Sun shower

The sun is out, but rain is falling from a dark cloud overhead, sparkling and shimmering like jewels in the vivid light, which itself seems fresher than it does when no rain is falling at all. This is a sunshower -- known by the romantic name of "liquid sunlight" or "liquid sunshine" in Hawaii -- a weather phenomenon that sometimes happens during the warmer months in the temperate zone, or at any time in the tropics.

A sunshower seems mysterious enough to the casual observer for many superstitions to arise about it, ranging from arguments between the devil and his wife to the idea that sunshower rain is lucky if you are caught out in it. Sunshowers are often even more noticeable because they are favorable places for rainbows to form. However, there is nothing particularly mysterious about a sunshower, which is the result of cumulus cloud formation.

Cumulus clouds are white, cauliflower-like clouds which vary in size from fluffy, amusing midgets on a warm afternoon to colossal white towers that may develop into thunderheads. If a cumulus cloud grows vertically beyond a certain point, it begins to penetrate multiple layers of atmosphere, transmitting heat and moisture upwards in powerful updrafts. Eventually, this moisture starts to condense out into raindrops.

Large cumulus clouds, called cumulus congestus, can produce showers of rain that are brief but can range from fairly light to fairly intense. Because the cumulus cloud develops vertically upward into the atmosphere, and can be much taller than it is wide, there is plenty of space for the sun to shine in around the edges of an isolated large cumulus cloud. This is especially true in the afternoon, when the sun is sinking and the rays can angle in under the cloud base. This is the origin of almost all sunshowers -- although an isolated thunderstorm (which is a cumulus cloud grown so large that it is capped by the stratosphere and becomes electrically charged due to the power of its updrafts and other circumstances) can produce sunshower-like effects as well.

Sunshowers are held by some to be a sign of wetter weather on the way -- and, unlike the idea that the devil is flogging his wife and the rain is her tears, this opinion has some basis in fact. The presence of sunshowers means that there is a lot of moisture and heat in the air, and that this is rising in updrafts -- in short, that the atmosphere is highly unstable. With the right catalysts, these conditions can easily lead to rain -- so a sunshower may indeed prove to be a herald of more rain, even though it does not directly cause that precipitation.