How to... Sense check the forecast

Want to know exactly what the weather is going to do? It's time to look up from your phone, says RYA British Sailing Team meteorologist, Simon Rowell...

There’s so much weather information available on your phone that sailors are becoming more and more dependent on the data - true for beginners right up to experienced professionals.

Yes, by all means pull up your favourite forecasting website and have those numbers written down to feed into your race strategy or passage plan, but then you should also try to get an understanding of what’s driving the weather for that day.

Start your day right. Get yourself a cup of tea, then go outside and or up on deck and just have a good look at what’s going on. Is it raining? Are there any clouds? If so, what direction they are coming from?

If you’ve moored up overnight or anchored somewhere, it’ll be sheltered - that’s the point! – so often the wind that you get around your boat first thing in the morning has no relation to what’s happening outside the marina or just round the headland. However, the clouds are at height, way above all the obstructions caused by the land, so they give you the best indication of the actual conditions.

Now you can go back to your phone. Look at a synoptic chart and work out what system is driving the weather for the day, whether it’s a low or high pressure, or changing from one to the other.

It can also help at this stage to look at a satellite image; in the UK for example the Met O ce website has a rain radar, which shows fronts coming through, and is really useful because that’s actual, known information as opposed to a forecast.

Once you are out on the water, you can put all this information together with some observations. You know what the numbers are telling you, and you know what is driving the weather. So, look out for signs to confirm any changes you are expecting. For example, if you are expecting the wind to shift right at 2pm, and you also know a front is coming through and that’s what is likely to be driving that shift, keep an eye out for the clouds becoming deeper, darker and lower as that front approaches. If they’re coming in at roughly the right time, you can think ok, maybe the wind will actually go right at 2pm, but if the clouds stay away or arrive earlier, then you know the shift will be delayed or come through sooner.

So, use your forecast to get a big picture of what’s happening, find out what’s driving it and then look at the detail - visual clues and things you can sense or feel will give you the best insight as to what’s actually happening. That way you can apply the forecast without having to be on your phone all the time!

Simon Rowell is an RYA Yachtmaster Ocean Examiner, has an MSc in Meteorology, and is the author of Weather at Sea. Find out more at rowellweather.com