24 Mar 2015

DIY weather forecasting – sunshine and showers

We’ve all been there where we’ve popped out for lunch to get a sandwich with sunshine overhead, only to get caught in a heavy downpour on the way back – often much to the amusement of friends.

That’s the peril of sunshine and showers. Do I take an umbrella, or take a gamble and risk getting soaked?

Now, I’m not trying to talk myself out of a job here, but I thought I’d share with you some handy DIY weather hints that will help you figure out if a shower is coming along and hopefully spare you the embarrassment of getting drenched!

Appearance of clouds

Taking a closer look at clouds can actually give a good indication of the likelihood of showers falling from them.

When heading out, have a look around the sky to see which clouds are in the vicinity and take note of their appearance and how high they tower into the sky. The general rule of thumb is, the darker and taller the cloud, the higher the chance that it will produce showers.

Cumulus clouds, also known as fair weather clouds, are known for their cotton wool like appearance. These are white and don’t reach very high into the sky. If you see these drifting around overhead, you’re more or less guaranteed to stay dry as the chance of a shower is extremely low.

Cumulus mediocris clouds are the next step up from cumulus clouds. They have a similar appearance, but start to reach a little higher into the sky. Despite looking a little more mischievous, apart from the odd light shower it’s like to stay mainly dry.

Cumulus congestus or towering cumulus clouds are when you really need to think about grabbing the umbrella.

These clouds reach higher up into the sky and are more developed, with a cauliflower-like appearance. They also appear grey as more light is reflected back into space from the top of the cloud, giving the base a darker appearance.

There is a good chance that these clouds will produce showers, which could be heavy and last for 15 minutes or more.

Finally, the king of clouds: cumulonimbus. These clouds rise way up into the sky at the height at which planes fly – 30,000ft or more. At this stage, the tops of the clouds consist of ice crystals rather than water droplets and can produce intense downpours, with hail and thunder.

A shower is more or less guaranteed from these clouds and they often last at least 30 minutes and sometimes hours if they are slow-moving.

Speed and direction of clouds

If you’ve worked out the type of cloud, the next thing to note is the speed and direction. Getting a sense of where a cloud is heading can give you a good sense of how long it will take to reach your location.

If you see a huge towering cumulus cloud some distance away but it appears to be very slow-moving, then it may be some time before any showers reach you.

Onset of a steady breeze

This is a particularly good warning of when a shower is about to happen – especially when used in conjunction with the other points I’ve already mentioned.

Before a shower arrives, there is often a sudden steady breeze that occurs. This is because as rain falls from the clouds the air below is pushed downwards creating a downdraught. This air sinks and spreads outwards when it hits the ground, giving this sudden breeze. This breeze can be gentle ahead of a light shower to quite strong just before a torrential downpour.

Rain in the distance

If you’ve ever looked at shower clouds across the horizon, you may have noticed a grey, translucent shadow reaching from the base of the cloud to the ground. This is actually rain falling. Sometimes you can spot these beneath nearby clouds and you can work out if they are heading in your direction.

So now you have no excuses for getting caught in a downpour and you can impress your friends when you’re heading out for lunch and dodge those showers.

Don’t forget, you can get the latest forecast on the Channel 4 Weather website and you can contact me on Twitter – @liamdutton

Images courtesy of NOAA Photo Library

Tweets by @liamdutton