Summer in the UK is once again a washout, and although we are close to breaking point we do understand that without rain, life would be incredibly uncomfortable. The weather forecasts are peppered with phrases such as:

• Cloudy with showers
• Showers, heavy at times
• Outbreaks of rain pushing northeast
• Blustery showers
• Changeable
• Unsettled
• Thundery showers

No doubt, you might notice a theme occurring. Although you may feel you fully grasp the wonder of the water cycle and the role precipitation plays, it remains to be seen exactly how much we really know about rain.

Rain comes from clouds, but did you know that clouds can be broken into 4 categories, and not all of these clouds produce rain?

1. High clouds – Cirrus, the thin, wispy clouds formed of ice crystals representing pleasant weather.
2. Middle clouds – Alto, these blue/grey clouds are comprised of ice and water droplets, and usually form a continuous block in the sky. They are often a precursor to rain or storms.
3. Low clouds – Stratus, resemble fog and produce drizzle or mist.
4. Clouds with vertical growth – Cumulus, the light fluffy clouds we often associate with fair weather days. It’s when they begin to grow upwards that they transform into the huge cumulonimbus thunderstorm clouds that you need to take cover from.

Educating ourselves about clouds can not only provide an endless source of entertainment (remember cloudspotting as a child?), but as weather experts say:

“Not only can clouds make great photographs, but they can also provide insight into approaching weather”- Weather Works

We have seen how rain can be produced through evaporation and how our planet is in part able to survive because of this, but just what are the different types of rain, and how are they formed?

Frontal rain

Frontal rain occurs when a cold, dense air mass meets a warm, lighter air mass. The incompatibility forces the warm air up and over the cold air creating the ‘front’ that we hear about in weather forecasts.  The resulting warmer air cools and condenses as it rises, producing raindrops. Frontal rain produces mild to heavy rainfall.

Orographic or relief rain

Orographic, also know as relief rain, is produced as a result of sweeping winds picking up moisture from the sea and carrying it up over the mountains to form clouds as it cools. The clouds then disperse rain as a form of relief.

Convective rain

Convective rain is produced by the cumulus type of clouds that we associate with very heavy showers and thunderstorms. The vertical growth cloud is formed when the ground is heated from the sun forcing moisture to evaporate and rise. As the moisture rises it cools and condenses into clouds which continue to expand until the point of expulsion. Due to the instability of temperatures these clouds can cause thunderstorms and torrential rainstorms.

In some cases, the forces of weather can combine. All three types of rain may occur, leading to severe flooding, which we all know can be just as disastrous as a lengthy dry spell. There are many reasons to celebrate rain, and with inventions like rainwater harvesting, more and more of our rainwater is going straight into clean water supplies and being put to good use.

[Photo by xusenru]