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The clouds are a key to reading weather conditions. If you know the clouds types you can work out whether to get out on the water and when to come in.   

How often do you watch the weather on TV expecting a fine day of paddling only to be greeted with stronger than forecast winds, wind coming from a different direction or worse, rain! As I am sure that you are aware, forecasts are predictions and any prediction has the potential to be wrong.

It is important to appreciate that any weather prediction is based upon an average and not, exact, wind speeds or cloud base. Where weather forecasts become increasingly unreliable are in coastal locations, near thin land peninsulas and areas facing large expanses of water, e.g. the Atlantic, Pacific or Indian Oceans. Or, geological formations which alter weather patterns, e.g. high mountain ranges, valleys or the great lakes in north America. 

Irrespective of whether you live in any of these areas, the following is an intriguing way to better predict the likely conditions just by recognising the type of cloud forming in your region. 

THE BASICS 

In general, specific clouds will be found at specific heights and can be classified as being either:  

  • High
  • medium, or 
  • low level cloud

Knowing which height these clouds occur at can help us to identify where we are in a weather system and therefore, the weather we are likely to encounter.  

  • High clouds will have the prefix Cirro.
  • Medium level clouds will start with Alto.
  • Low level clouds will appear without a prefix using their name only e.g. cumulous (fluffy cotton wool type clouds) or stratocumulus (strato = layered).  

Finally, there are clouds which can be found transcending all levels and can be of great vertical height like the nimbostratus or cumulonimbus or perhaps the fair weather cumulous clouds like those found on the Simpsons. 

SO WHAT DOES IT ALL MEAN? 

Very simply, weather systems with different air temperatures, like oil and water, do not like to mix. Specific clouds will only be found in a specific air deck (height). Knowing which cloud can be found in which air deck gives us valuable information of the likely weather over the coming hours.  

Clear skies, as you already know, generally means good weather and is associated with warmer weather or high pressure systems – this means that air is descending, creating greater pressure on the Earth’s surface. Descending air suppresses cloud formation.

Low pressure is the converse, usually cooler, with air rising, hence lower pressure on the Earth surface with cloud formation as water vapour condenses. We can tell where we are in a weather system by looking at the clouds.

IS A WARM OR COLD FRONT APPROACHING? 

  • Approaching warm front: Cirro, cirrostratus, altocumulus, altostratus, nimbostratus and stratocumulus 
  • Approaching cold front: cumulus, altocumulus, cumulonimbus 

We know that a warm front/sector is approaching because we have seen the cloud base lower throughout the day starting with Cirrus all the way through to nimbostratus. Generally visibility will become poorer with the potential for mist or misle and this can bring with it fog if warm air travels over cooler water or ground. Quite often the wind will be light and remain stable e.g. stay within the direction it has been blowing in at a similar or lighter strength.

There is a handy rule of thumb which can be used; whatever cloud type is most prominent at mid morning is the likely weather to be with us for the next four to six hours. Another is to notice when cirrus clouds first appear, make note of the time and if the sun becomes covered by thickening sheets of cirrostratus, rain is due soon. More specifically, if four hours have passed from when cirro clouds first appear to when the sun is covered, this will likely be the amount of time it will take for it to rain. 

Cold sectors approaching indicate the potential for more turbulent weather, usually when towering cumulonimbus clouds start to appear. Any cloud with great vertical ascent means that there is greater energy in the atmosphere and more potential for more rapid change either in wind strength, direction or rain.  

Knowing the difference between nimbostratus and cumulonimbus is important, because cumulonimbus only occur at the beginning of a cold front. What this means to us is potential squalls when out on the water as these towering giants lumber towards us. Wind speeds are likely to increase markedly, and very likely to change direction by as much as 180 degrees. If we see these on the horizon, we should question whether the change in weather is likely to occur while we are out on the water. If so, should an alternate route be taken, one with greater shelter from natural features e.g. headlands or tree lined banks or shores. 

A nice rule here is something called the Buys-Ballots law. In the northern hemisphere when standing with your back to the wind, the low pressure will always be on the left. What this means is weather is likely to deteriorate if, when the wind is on your back, clouds are moving from the left, if clouds are moving in from the right, weather is likely to improve and if the clouds are following with wind current weather will remain the same.  

In the southern hemisphere, a similar principle applies, however, we reverse the rule e.g. the low will be on the right instead of the left. 

BOARDSHORTS OR WETSUIT? 

Now you have some general principles to work off which may help you decide if you need board shorts or a wetsuit to go paddle, and more importantly, whether getting on the water at that time is a good idea without making amendments.  

Watching clouds can be something we easily overlook, but once we take notice it can be an amazing way to engage with the environment and the world around us. 

The general principles are just that, general, and a significant amount of detail can be added to this content.

Great books which can be used to learn more about this fascinating area include: Reading the Clouds by Oliver Perkins, The Weather Handbook: An Essential Guide to How Weather is Formed and Develops by Alan Watts, and the RYA Weather Handbook by Chris Tibbs.

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