The wrong kind of weather:
We Brits are always talking about the weather. So much so that even when we encounter people from the other side of the planet they seem to bring it up just to make us feel at home. Or is that just me? Seriously though these islands are known for their changeable weather, some of which can be less than desirable meaning we should be prepared when venturing out. Even with the best will in the world and the highest level of planning there are times when the weather just seems intent on catching you out and causing you the maximum amount of trouble. This being the case it is useful, sometimes crucial, to be able to recognise the signs that the weather is taking an unexpected turn for the worse.
Although the consequences of not noticing it’s about to pour for most of us in our day to day lives simply means getting back from walking the dog slightly on the soggy side, it can have much more serious consequences. People who spend any length of time outside in this country will tell you that they very rarely go anywhere without their waterproof stuffed in their rucksack, even on a beautifully sunny day. The reason for this is simple, within an hour the weather can turn from balmy to lashing down and life threatening. This may seem an over the top statement but in the wrong circumstances and conditions hypothermia can set in very quickly. Hopefully the following short article will provide an insight into recognising approaching weather systems predominantly through recognising cloud formations.
Not to bore you but we’ll first of all start with a short recap of some those basics learnt at school during science lessons. The best way to remember what is happening to air during the formation of clouds is to think of those frosty December mornings that aren’t too far away. When you breathe out on such a morning the warm moist air from your mouth comes into contact with the cold external air. Warm air when coming into contact with cooler air starts to rise. As it does so the warm air starts to cool and subsequently condense into clouds. So the plume of steam that you breathe out on cold mornings is cloud formation in miniature.
There are three main factors that can affect the upward movement of air and the resulting condensation. These can work independently or in combination with each other depending on the local landscapes and environment.
- Weather systems: One air mass lifting another. These are large systems that sweep over the country.
- Convection: Warm, moisture bearing thermals rise and then cool. This can occur on both a large and small scale.
- Mountains: damp air is lifted over mountains and cools as it does so.
So let’s look at the variations in cloud formation that can occur and how we can interpret them in order to predict changes in weather. The progression very high wispy clouds (Cirrus type) through to lower and lower layers (Stratus type) indicate an approaching warm front. The higher Stratus layers know as Cirrostratus (see figure 2) can often form a halo around the sun or moon. A halo around the moon is often a good indicator that there will be rain in the morning. You can refine the estimate of the time the rain will take to arrive by clocking the time of progression from Cirrus to Altostratus (the layer that is thick enough to block out the sun or moon). The time it took for this progression is roughly the same time it will take for the rain to arrive.
With the approach of a low pressure the high altitude clouds will move in a different direction to those below. This can have a very easy application for those of us sitting around a camp fire. Should the smoke from the fire be moving in a different direction for the high wispy clouds then this is a reliable sign that changing weather is approaching.
Cotton wool clouds:
Cumulus clouds show where there are cells if rising air. If these balls of cotton wool stay relatively low and self contained then the air mass is relatively stable. Only if the cumulus clouds expand upwards (becoming cumulonimbus clouds) do they indicate unstable weather. This formation of cloud can even reach the tropopause (the stable area of atmosphere above the troposphere where all our weather happens) forcing them to spread out potentially causing thunder and lightning storms, often associated with hail storms.
So although these tips for recognising changes in the weather will never surpares an modern ‘accurate’ weather forecast they are extremely useful for helping you stay in touch and fill in any uncertainties left by the forecasters. On another note these skills allow a more deep understanding of the environment around you and what it is doing, meaning you can react and respond to it in an appropriate way. After all Bushcraft is all about being in touch! So get out there stay safe and enjoy.
Danny Hodgson- Apprentice Instructor