Reading weather forecasts to help plan a day out in the mountains.
This blog is all about weather forecasts - how to read them, which ones to read and how the information can help make our time out in the mountains more enjoyable and safe.
Most people do check the weather before heading out out for a walk in the mountains. It's common sense. The first mistake some people make is checking the wrong forecasts. Mountain weather has it's own characteristics and so there are specific mountain weather forecasts.
The most common forecasts people use are Met Office & MWIS. I also use Mountain-Forecast.com. If you use the Met Office forecasts, It's important that you search for the mountain ones. You can find forecasts for specific mountains, ranges and areas within the National Parks on both the Met Office and Mountian-Forecast.com websites. MWIS (The Mountain Weather Information Service) offers area specific forecasts and is very good at it.
Different forecasts will give you the information in slightly different ways but will usually fall into two categories: detailed hourly or general forecasts. It is good to get in the habit of checking and comparing them both for a few days ahead and then the night before your walk to help decide if you need to adjust your route. Forecasts are usually updated late afternoon for the following day. There will sometimes be contradictions between the predictions but more often than not, they will be quite similar. The predictions that match the closest will usually be the most reliable. The two main things a weather forecast will help us decide are where we go and what we take. Below are forecasts from both MWIS & Met Office for the same area on the same day. The pictures further below are also from the same area and day. Try to see where they match and where they differ.
Some key questions to ask when looking at the weather forecast will be:
Is it going to rain?
Rain predictions can be funny. Sometimes they can be well off and others, perfect. It is always worth looking at the detailed forecast where it will give you the % chance of precipitation (rain) for each hour along with an indication of how heavy it might be. It shouldn't surprise you that black clouds with multiple rain drops mean heavy rain and lighter clouds with one drop, not so heavy. If a forecast says 10% chance of light rain at 0900, it could just mean that there is a roughly 10% chance it could rain somewhere within that hour, not necessarily for the whole hour. This section will display whether precipitation will fall as rain or snow.You can also look at the rainfall radar and see where the rain is, relative to a particular area, in real time. This can be a great tool if you are planning to go scrambling. It can enable you can look at your route timings and avoid the worst of it by leaving earlier or later. A good idea is to store your kit in dry bags inside your rucksack. Don't waste your time with rain covers as they are prone to blowing away in the wind. Another consideration when rain is forecast is whether there are any river crossings on your route. Even an hour of heavy rain can significantly increase the flow of water down a river.
How hot or cold is it going to be?
Hot, sunny days are not as pleasant for walking as you might think! They are great for lounging around or going for a scramble but can put a lot of strain on you when out walking. When the forecast is really hot, chucking a few extra items in your bag can make a real difference. A small tub of sun cream, a spare baseball cap and even some dioralyte type sachets for can be useful to prevent dehydration setting in. You could easily drink 2-3L of water on a hot summer walk so maybe carry an extra bottle of water or a filter for topping up at streams. If you take a dog on hot days, plan a route with water stops at lakes/rivers. Whatever the weather, always take a warm layer! It might sound obvious but it is colder on the top of the mountain than the bottom. The temperature will drop by around 1°c for every hundred meters you gain in altitude. It could be a mild 10°c at the start of the Pig track (about 360m) but by the time you get to the top (about 1080m) and even without windchill it will probably be around 3°c. You will also get a 'feels like' temperature.
What is the average wind speed?
An average 25mph wind speed blowing onto that 3°c summit temperature will probably make it feel below freezing; You will feel this even more so when you are sitting down and damp with sweat from the climb... Being wet increases cold. Remember that there will usually be gusts of wind above the average speed. A 25mph forecast could come with occasional 40mph gusts, which could easily catch you off guard. This is known as buffeting. Does your route take you on or near steep ground, might that wind blow you towards it? Should you change your route? Who will be with you and how will they cope with it?
What direction will the wind be blowing from?
The direction shown on the forecast is the direction that the wind is blowing from. It might be that the forecast is for a South Westerly (SW) wind meaning it will be blowing from the South West, to the North East (NE). Could you plan a route that is on the sheltered (the lee) side of the mountain, and keep out of that wind as much as possible? The direction the wind is blowing from will also affect the temperature of it. Northerly winds will often be biting cold and bring snow. The prevailing (most common) wind in UK is SW, which comes in from the Atlantic ocean and brings the common wet and windy weather we know and love.
If you're planning on a wild camp, knowing whether the wind will increase through the night and from which direction can help you choose a sheltered location and get a better night's sleep or even stop your tent getting blown to pieces.
What will the visibility be like?
Low cloud might mean your choice of route will need solid navigational skills. Remember to keep constant track of your progress, making notes of key features both passed and expected. There's no point leaving it until you can't see your feet 10m ahead of you to try and figure out where you are! If the cloud-base will be around 800m, why not do a walk on a 600m mountain and get some views? It's the small wins that make our life easier. I provide navigation training courses, if you would like to come and spend a day or two learning. Drop me an email or check out the website if you'd like to know more.
What time will the worst of the weather will be arriving?
If the weather looks to get progressively worse, how about setting your alarm nice and early for an apline start or alternatively, if it looks like it's going to start off bad but improve, how about calling in to a local caffi and having breakfast first?
What time is sunrise/sunset?
Will it be possible you might end up walking back in the dark? Am you happy with this? Can you avoid it by choosing a shorter route, setting a turn around alarm on your phone or reduce the risk of getting lost by making sure you're on a solid path before it starts to gets dark? Keep your headtorch fully charged and stored in your bag in an easily accessible spot. Always check it before you pack it. I have a head torch that locks so it can't go on accidentally. I also have a spare one which doesn't, so I reverse the middle battery while it is in storage to stop it working. Always reverse the same battery. Catching the sunrise from your favourite mountain is a magical experience. You might look at the forecast on Thursday and see that Saturday looks better than Sunday or vice versa, and know that sunrise will be at 07:50 and be able to plan your journey accordingly.
At different times of the year, there may be additional considerations.
In winter, you should also be looking for hazards like snow and ice which need special equipment such as ice axe and crampons. There will usually be a section on 'ground conditions'. Asking around on social media can also be useful as people may have been where you are planning to go. Just be cautious what advice you take as sometimes people can give poor advice with good intentions. It's good to get a summer or two under your belt before considering winter walking. Building up your skills and confidence with things like navigation, planning and kit will give you the best possible chance of having a brilliant and safe time. I learned this the hard way. If you are really keen, maybe look for an instructor to teach you some winter skills.
In Summer, there can be a risk of things like thunder and lightning and planning around the possibility can give you the best chance of avoiding the danger. If you ever get caught out with a freak thunder storm, getting off the hill as soon as you can is usually your best bet and planning any route should always come with escape options. We'll look at route planning in another post.
All this information is available to us on any day of the week. It might seem like a lot to take in now but after a while, it becomes second nature to think about and five minutes looking it over can either give us confidence, set alarm bells or just enable us to be a bit savvy with our time. Flexibility when planning your day out and then adapting to the conditions when on the move are really important skills. A little bit of knowledge and some planning can save us from so many unnecessary problems.
If you have any questions, please feel free to drop me an email.