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In the tenth instalment of our Sea Signs series William shares techniques to read clouds.


10. CLOUDS.jpg


Until very recently I knew nothing about clouds. But when I decided it was time to start taking steps to realising my life’s dream – to get a boat and sail it around the world – I set myself the challenge of learning the difference between my cumulus’ and nimbuses. With my head in the clouds I dreamt of using them to navigate across oceans and predicting the weather. So, equipped with my Haynes Meteorology Manual by the superbly named ‘Storm’ Dunlop, I set to work – and it taught me some unexpected lessons. Perhaps most importantly, Cloudspotting taught me that days of relentless grey cloud [the NimboStratus, codename Ns] is not a reason to sink into a weather-related depression, but an opportunity to celebrate the workings of nature. “Lovely example of Ns today,” I emailed fellow cloud enthusiast Jay, to which he replied, “Yes, a day that only a true cloud fan could delight in!”


There are ten main cloud types and their names are made from five key words; cumulus, stratus, nimbus, cirrus and alto. Each word has a meaning that helps describe the clouds’ character. Cumulus means ‘fluffy’, Stratus is a layer, Nimbus brings rain, cirrus are ‘wispy’, and alto are found at mid-altitudes. When two of these keywords are put together you can get a clear image of the cloud: StratoCumulus is a layer of fluffy cloud, CirroStratus is a layer of wispy cloud, and NimboStratus is a layer of rain cloud. The two main rainclouds – NimboStratus [Ns] and CumuloNimbus [Cb] – have very different personalities. As a general rule, Ns is a blanket of grey with long periods of rain, while Cb forms amongst blue skies and gives short bursts of heavy rain and hail. 


This difference led to the success of my greatest Cloudspotting achievement to date; stepping out of a café and identifying the cloud above me as a CumuloNimbus, just by the feel of its rain. The fact that the hail was hammering down while the sun was still shining told me it could only be a Cb towering above. These conditions prevailed for a week; short bursts of rain followed by bright blue skies. It made outings with two young children, both under 5 years old, a complete rigmarole. Do you spend an eternity squeezing them into wet weather gear, despite the sunshine, in the off chance you get caught out in a shower? Or do you take your chances and risk a soaking? I adopted the latter strategy, running for the closest beach shelter every time we got ambushed by a rogue CumuloNimbus. 


On the evening of Friday 27th July 2018, the moon, sun and earth were in a particular alignment that meant the earth was blocking the sun’s rays reaching the moon – a rare event known as total lunar eclipse. The anticipated effect was the changing colour of the Full Moon from bright white to dark red, so we organised a picnic on the beach with friends to enjoy the spectacle. However, a rapidly approaching squall line shattered our plans and we evacuated to the van for supper in there instead. Amongst the chaos of four children, four adults and a water spaniel squeezed into 6 square metres, I wrote in my ‘Nature Notes’ journal:


The clouds may have obscured the rare ‘Blood Moon’, but it was fascinating to experience this intense change in weather that follows a squall line. And while a Shelf Cloud warns of what is about to come in the next few moments, other clouds allow you to predict conditions in the coming days. A typical warm front coming off the Atlantic is wonderfully demonstrated through a model in the National Maritime Museum, Falmouth. It’s made from Perspex and filled with clouds, mounted on runners above a map of Cornwall. As you slide the model from West to East, a screen shows the order that clouds pass. Firstly you get the high Cirrus warning of what’s to come, then a gradual deterioration climaxing with the NimboStratus rain cloud, with strong winds.


Last summer I helped my friends’ dad sail his yacht back to Britain from Brittany. We left the French coast just before 4am and by mid-morning there was no sight of land in any direction. We were in splendid isolation, except for the occasional cargo ship and a pod of dolphins. But as the day progressed the first signs of Cornwall appeared; a line of Cumulus hovering above the horizon. These fluffy white clouds are made by warm air rising until it reaches its dew point and condenses into cloud. Because land heats up faster than the sea during the day, Cumulus are often well developed along the coast in the afternoon. This makes them fantastic navigational aids and I was delighted to join generations of seafarers who have used these clouds to get their bearings. 


We moored in Falmouth that night alongside a colossal Royal Navy auxiliary ship, then made our way to Plymouth the next day. The air was thick with moisture and a mist crept in. Technically, when visibility reduces to 1,000 metres mist becomes fog. Known as a ‘Haar’ in Scotland and north-east England, Sea Fog is a low-lying cloud that forms when warm air blows over a colder sea, cooling to its dew point and condensing into a cloud. 


A threat to navigation, Sea Fog can appear suddenly and last for days. Luckily we had a radar on board, but if you’re in a dinghy/paddleboard/kayak I’d recommend taking a compass and VHF on all adventures in case you get enveloped. If you do get caught out I have a tactic that might work; work out the direction tidal currents should be flowing along the coast and head perpendicular to the stream until you reach land. 

In the next Sea Signs feature William will stay in the skies and explore how the sun affects adventures, sharing tips for navigating by the great ball of fire.

About this series

Every day the sea is different, a  result of the ever-changing interaction between the moon, sun, tides, wind, waves,  buoys, boats and the beach. While the picture may appear complex, like a piece of classical music, it is essentially just an arrangement of simple elements, or notes. By dismantling the machine into its component parts and exploring each one in detail we can create order out of chaos; clarity out of confusion. That is the  purpose of this series 'Sea Signs'.

When we are young we learn to navigate urban environments; what traffic lights  mean or how to cross a road. What many of us aren’t taught is how to read nature’s  signposts; how to judge wind by watching birds or what weather different clouds  bring. Then there’s a whole technical world of buoys and boats with different light  sequences, colours and signals communicating messages. My goal in this series is to  share with you all the signs – both natural and man-made - that you may encounter in  your adventures along the coast so you can read them as well as any yachtmaster  skipper or crusty old seadog. 

With this knowledge, nothing is going to slip under your radar.

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