A temperature inversion at the summit
The weather is going to make a lot of difference to your day on Snowdon (Yr Wyddfa), but whether it’s glorious or appalling, it’s important that you’re prepared for it.
Wherever you live, the internet will give you a reliable forecast for Snowdon (see the links below). We’d recommend looking at more than one site, and checking them several times in the days before your visit, and even in the hours before your visit – conditions often change quickly.
Don’t just look for sun and rain in the forecast; check the temperature, and also the wind direction and speed.
Note: Remember that weather forecasts are not infallible; they are only a prediction and don’t always agree – you could call them an educated guess – and they can sometimes prove wrong. (Sometimes forecasters say that they have ‘high confidence’ in a forecast, and at other times ‘low confidence’, but this level of confidence is not shown in computerised forecasts, which most non-verbal ones are.)
Mountain weather
“Climate is what you expect; weather is what you get.”
This is very true of Snowdon, where the regular seasonal patterns often don’t seem to apply so much. It has been known for walkers in summer to be treated for the first stages of hypothermia, and for walkers in winter to suffer from sunburn. These are, of course, exceptions, and checking a forecast will show the prevailing conditions at the time.
One important thing to be aware of is that the weather often changes as you go up any mountain; the weather at the summit of Snowdon will often be very different from the base of the mountain.
Remember that mountains often attract cloud (and therefore mist and rain), so even when it’s fairly sunny away from the mountain, you may have a day on Snowdon where you don’t see much sun.
Mountain weather is also often unpredictable, and conditions can change quickly. At its worst, strong winds, low cloud and freezing temperatures can make visibility and walking very difficult.
Temperature
The temperature is usually at least 7°C or 8°C colder at the summit than at the foot of the mountain,* and at most times of year the wind chill will increase this difference, sometimes considerably.
During the spring and autumn the weather can often reflect the seasons on either side – sometimes summery, sometimes wintry.
Be aware that even in summer it can sometimes be very cold near the summit; it is not unusual, even in mid-summer, for the wind-chill temperature at the summit to be close to, or even below, zero. You can be ready for the conditions by checking the forecast.
On a cold day take plenty of warm clothing, and at any time of year it is wise to take extra layers and waterproofs. (See the pages on kit and safety.)
Remember that the temperature forecasted is always the temperature in the shade. However, there’s very little shade on the mountain, so on a sunny day it’s likely to be much warmer than the forecast shows. On a hot day it’s wise to take sun cream.
* When the air is dry the temperature drop is about 3°C per 1,000 ft / 300m ascended; when the air is saturated the temperature drop is somewhat lower. It is therefore practical to assume an average of at least 2°C temperature drop per 1,000ft (300 m).
Mid-July 2022, and this forecast shows the changeable nature of the temperature at the summit from one day to the next.
Wind
If the windspeed is anything above 30 mph, you need to take serious note of it.
The Beaufort Scale defines any wind over 32 mph as some sort of gale.
The following table describes the effect of windspeed on a walker:
| mph | Beaufort scale | Effect on walker |
| 4-7 | (light breeze) | Wind felt on exposed skin |
| 8-12 | (gentle breeze) | Hair ruffled, loose clothing flaps |
| 13-18 | (moderate breeze) | Hair disarranged |
| 19-24 | (fresh breeze) | Walking inconvenienced |
| 25-31 | (strong breeze) | Steady walking difficult, knocked sideways by gusts |
| 32-38 | (high wind / near gale) | Walking with great difficulty and your foot not always landing where you intended. You may have to stamp your feet to walk. |
| 39-49 | (gale) | People blown off feet, walking becoming dangerous |
| 50+ | (severe gale) | You may be blown over, or blown several metres by gusts. Walking extremely difficult: progress may be crawling at times. Even lying down you may be blasted around by the wind. It’s worth linking arms as a group to keep smaller people anchored down. |
Winds are rarely constant and steady (if they were, walking in a wind would be much easier), and gusts can be particularly dangerous, often coming out of nowhere and throwing you off balance, so check that too (the Met. Office forecast for the summit shows both wind and gust speeds). Gusts of over 30 or 40mph can considerably affect your balance and progress, especially on the upper, more exposed part of the mountain. In winds of over 50mph it becomes near impossible to walk. Indeed, attempting to walk on Snowdon in winds in excess of 50mph is simply dangerous, and there is every risk of being blown over and suffering injury. (Even if you’re not likely to be blown off an edge, being blown over or into a rock can result in a broken limb.) And even if it’s only gusting at these high speeds, you really should consider cancelling or turning back.
Cloud cover
The symbols on good websites (see below) will indicate whether the sky is forecast to be overcast, partly overcast or clear. (See also this Met Office cloud cover webpage.) What they don’t generally show, however, is the height of the cloud-base, but this is a factor worth taking into consideration.
In an ideal situation, any cloud will be above the height of Snowdon summit (1,085m) so that there will be extensive views around in all directions. However, when the cloud-base is lower than this, the summit will be in cloud (i.e. mist or fog depending on its density) and views will be non-existent. Mountains like Snowdon tend to attract cloud, and sometimes, even if the general cloud-base is higher, the summit or upper part of the mountain can attract localised cloud, which can be very irritating! The best website for showing the cloud-base and low cloud is www.windy.com, but again it only shows generalised cloud-base heights.
Thunder & Lightning
If the forecast is showing thunder and lightning, it is strongly recommended that you stay away from high ridges and summits. If you do find yourself out when there is lightning around, aim to get to lower ground. The higher and more exposed you are, the greater the danger. However, only descend if it’s safe to do so, and then do so carefully, especially if it’s wet.
You should also minimise contact with the ground and any conducting objects where possible. Good advice is to crouch or sit on top of an insulating material such as a rucksack or a sit mat, and then put your hands on your knees rather than touching the ground. Although they don’t significantly increase the risk of attracting a strike, it’s wise to lay metal items, like walking poles, aside until the storm passes. If you are in a group, keep a space between you and others.
It’s safe to touch someone who has been struck by lightning and provide them with CPR or First Aid if it’s needed. Anyone who is struck by lightning must seek medical advice as soon as possible.
Winter weather
(See our full article on walking up Snowdon in winter.)
From early October onwards, Snowdon often experiences the changeable and stormy weather that the rest of Britain can face. Although this is only autumn, temperatures can get very low higher up on the mountain, and the first sleet and hail storms are likely.
Every winter, snow and ice can be present on the upper parts of the mountain from any time between the first week of November and mid-April. Most winters have spells of snow/ice conditions, interspersed with periods totally free from any snow or ice. It is impossible to predict what kind of conditions the winter will bring; for instance, February and March may bring appalling conditions where ice axe and crampons are essential, or may equally bring days of warm, spring sunshine with no snow or ice present.
In winter the Park publishes a twice-weekly report on ground conditions on the paths (usually the Pyg Track and the upper Llanberis Path) and at the summit. The report can be found here on Twitter and on the Park website here.
The summit in ideal conditions
The same view in less than ideal conditions!
Good weather forecast websites for Snowdon
The best sites are probably these three:
- The Met Office 7-day forecast for Snowdon Summit
- The MWIS (Mountain Weather Information Service) 3-day forecast for Snowdonia
- ‘Will it rain today?’ Met Office website (zoom in on North-west Wales)
Depending on which paths you’re walking on Snowdon, a forecast for the base of the mountain will also be useful:
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- Pen y Pass – Met Office 7-day forecast
- Llanberis – Met Office 7-day forecast or BBC 7-day forecast
- Bryn Gwynant YHA (for the Watkin path) – Met Office 7-day forecast
- Snowdon Ranger – Met Office 7-day forecast
- Beddgelert – Met Office 7-day forecast or BBC 7-day forecast
- Capel Curig – Met Office 7-day forecast or BBC 7-day forecast
Other useful sites include these:
- A more general Met Office forecast for Snowdonia (partly written by Met Office staff, rather than computerised, and indicating confidence)
- A Snowdon forecast from mountain-forecast.com
- Snowdon Live, detail from the summit weather station (only working during the season)