Mountain Skills Training: A Basic Understanding Of Weather

Properly understanding the weather and how it impacts on our day in the mountains is an important skill for us to have.

The following blog will be useful for novice hillwalkers and those who are taking their Mountain Skills training. It should give a basic understanding of what they need to know to make safe decisions on the hills.

Strong westerly winds on Scarr

The three areas we will look at are:

  1. Where to get reliable weather information?
  2. How we can interpret that information to help us plan our route.
  3. How we can notice and analyse changes in the weather in real time.


Where can I get my weather forecast from?

Some sites are more accurate than others and some are more reliable for specific types of weather, rain, wind etc.

So if we are going to put our faith in the online forecast then lets make sure we use reputable sites and that we crosscheck a few of them rather than relying on just one.

Also, don’t just check the weather report for the local town, but for the summits of the local mountains too, as there will always be a considerable difference between the two.

I would use the following sites regularly for weather forecasting and find them to be accurate:

But don’t just take my word for it, get familiar with navigating these sites, screenshot them before you start your walk and then at the end of the day cross check what actually happened with what was predicted. This can give you confidence in using a particular site, but also allow you to learn some of the nuances of mountain weather.


How we can interpret that information to help us plan our route.

In short, it will be colder, wetter and windier the higher we go. We should make sure we are prepared for this and that we take it into account when planning our routes.


Wind Speed:

Of all the elements, wind is the most likely to stop us from completing our hike or force us into making a change of route in the first place. Cold and wet days can be mitigated for with better gear, but wind will stop even the most experienced hikers from making progress or staying safe.

Wind speed increases the higher you go. As the air is pushed upwards by a mountain it is squeezed and increases in speed, making it more difficult to walk and increasing the wind chill factor.

The wind speed on top of a 1000m peak can be two to three times faster than at low level, which on a 25 km/h day in Dingle, could be very unsafe on top of Brandon Peak.

Below is an extremely useful chart for understanding what wind speed means in real time:

We should be aware that some forecasts only give us the average wind speed and not the gust speed. Gusts are short and intense, but faster than the average wind speed. Gusty days can make narrow ridges spicier than we might like.

Wind Direction:

Nobody wants to walk into the oncoming wind all day, especially wind driven rain or sleet.

We can use wind direction to our advantage when planning, so that when we are on the higher more exposed ground we have the wind at our backs assisting us rather than impeding our progress.

We can sometimes use the mountain itself for protection from the wind. On Scarr mountain in Wicklow for example, where strong westerly winds are common, it is possible to approach from the south (red) and contour around the east side (red dash) of the summit ridge, needing only to be on top of the summit for a short period. A good alternative route would have been to travel from Glenmacnass from the north, with the wind on your back and gaining ground on a wide spur (purple).

It is worth noting, that contouring isn’t always a safe option due to the terrain encountered. It can also be energy sapping and ankle jarring to venture off the well walked path, such as the one on Scarr, for the heathery less travelled ground on its east and if overused can impact on a persons overall enjoyment of the day.

Air Masses:

We must also take in the origin of the wind when looking at the wind direction and how this matters. Winds from the north are cold, winds from the south and east can be warm and drier while winds from the west can warmer and wetter.  The graphic below is an excellent concise description of what we need to know about air masses.

The Lapse Rate:

As we ascend in the mountains the temperature will get colder. We can quickly calculate an approximate summit temperature in advance by taking 1° degree Celsius off for every 150 metre of ascent.

To look at this in practice. You are parked at Cronins Yard, at an altitude of 140m above sea level and with an air temperature of 5°. You plan to climb Carrauntoohil which is 1040m at its summit.

We can divide the altitude gain (900m) by the approximate lapse rate (150) 6 times. If we take 6° off our air temperature at Cronins Yard, the temperature on top of Carrauntoohill summit will be approximately -1°, or below freezing.

This will obviously have an impact on how we need to prepare for our hike: the ability and fitness of the group, additional warm layers, extra gloves and hats, perhaps extra food and hot drinks in a flask and how the underfoot conditions on top might be.

Visibly below freezing on higher ground


As moist air is lifted over a mountain by the wind, it cools down, condenses and forms rain, known as Orographic rainfall. This type of rainfall creates a rain shadow on the opposite side of the mountain, with descending dry air. This side of the mountain can be drier and warmer than the opposite side. As per the drawing below.


With Lapse rate and Wind chill we looked at the temperature getting colder, but what about when the temperature is too high?

Overheating and over exposure to the sun are probably not our first thoughts when it comes to hiking in Ireland, but they have to be considered none the less.

On sunny days could we plan our routes to take benefit of the early morning shade from a north facing peak? Or aim for a ridge line walk to avail of whatever breeze is on offer? Or could it be as simple as an earlier starting time, to ensure the bulk of the walk is over by midday? Does my route pass a reliable clean water source during the day where we can refill our water bottles?

Rethinking what to carry on hot days is extremely important. Doubling the water you normally carry is good place to start. Suncream, rehydrating salts, blister packs, sun hats and sunglasses. We can pack and prepare quite differently for the rare sunny days we get, so don’t be on auto pilot when it comes to packing.

In this part of the world, the advice from the medical experts is that we should wear sun-cream if we plan to be outdoors any time between April and September, whether its sunny or not. We rarely think in the long term, but skin cancer is a serious issue and perhaps we should be more aware of the dangers of increased radiation at these times of year.


How we can notice and analyse changes in the weather in real time?


A basic understanding of clouds can teach us a lot. I find the Latin names and multiple varieties of clouds can be daunting and off-putting for those trying to learn, however, if we can understand the 4 main types of cloud, practically all the clouds we need to know are composites of them.

Nimbus: a cloud that carries Rain

Cirrus: high altitude, wispy, formed of ice crystals.

Cumulus: puffy, fluffy, cotton wool like, piles of cloud

Stratus: low level, layers of clouds


Using the 4 main types of cloud above, we can decipher the characteristics of other types of cloud and why we should know them.

Nimbostratus: for example, would be made up of multiple layers of rain carrying clouds, which will produce continuous rain and we shouldn’t expect to take off our waterproofs during the day.

Cumulonimbus: would be accumulated piles of clouds carrying rain. They can bring heavy rain, high winds and even lightning.

Cirrocumulus: these small, puffy and accumulated high altitude, icy clouds can be indication of stormy weather in the coming days.

Cirrus clouds  are high altitude, whispy clouds. When seen alone, they can be fine, however if combined with low stratus clouds, it could be seen as a sign that rain is on the way.

The extremely simple to use and concise “cloud guide” app is available to download for free and I highly recommend it.

Using it to identify the clouds and noticing how these clouds are changing characteristic is a valuable skill in the mountains.



Rainfall can have an impact on our route selection as much as our enjoyment of the day. If you have to cross a river as part of your route plan, could it be impassable due to heavy rain? Even if its not raining today, did it rain heavily yesterday or overnight and will this have an impact on the route choice.

A dry day, but recent rainfall making route progress tricky

Remember, rivers don’t swell in size at the exact same time as it rains, we have to understand the rate at which the rainfall runs off the land and into the river and this can have as much to do with the existing water content of the land as it does with the amount of rain that is falling.

For example, after a period of dry sunny weather, the ground can be hard and impermeable. This can mean that instead of the rain being absorbed by the ground it can run off it at speed on steeper slopes. This collects quickly in rivers and they can swell in shorter periods of time than if the water had “drained” into the river.

Likewise, an extended period of cold or freezing weather can harden the ground and not allow rainfall to soak in, again creating faster than normal run off into the rivers.

Being familiar with the response rate of rainfall to river flow is an important skill to learn. Will the stepping stones you crossed to get up the Hags glen still be above water when you come back that way 4 hours later?

If we fail to analyse or prepare for these possibilities we may be unnecessarily forced into an incorrect choice or action plan.



The MWIS forecast in the UK is great at informing the level of cloud cover. In Ireland we have no equivalent resource. Forecasting fog and cloud clover is not a simple process and probably not one we plan for like we do for rain and wind. Sometimes we wont know what the visibility is like until we arrive at the base of the mountain.

How we react to fog and low visibility is important however, If our route plan was to cover a large distance and/or lesser known ground then we may have to factor in the additional time we will spend navigating throughout and entire day. We may no longer be covering ground at the speed we had planned and erring on the side of caution might be a better option than trying to link up that last peak.

low visibility on Carrauntoohil


You could write a full book about the change that real snowfall and frozen ice makes to our general hiking in the hills, but for the most part a light dusting isn’t going to make that much of a difference underfoot to a regular hiker, but I would ensure my route plan doesn’t cover ground where snow has fallen on steep short grass as it can be extremely slippy underfoot.

Frozen sleet and snow near the summit, but not presenting much difficulty to the group

My main aims in planning a route over light snow would be to stick to wide spurs and gentler inclines when possible and limiting the time spent on rocky terrain where they may have become iced over. We must also take into account where the snow line is on the mountain. Is it just a light dusting on top or is there an inch of snow at the base? Obviously a small amount of snow lower down is an indication of much greater amounts up high.

If in doubt or unfamiliar with the route, play it safe and plan elsewhere.

The planned use of crampons and/or an Ice Axe is a different matter, but best saved for a separate blog.


In summary

We all love to be optimistic in the car park when it comes to the weather,, but we should never become complacent. How often have you started a walk in perfect sunshine only to be soaked by lunch?

Furthermore, if we are changing the route plan because of the weather, either before starting or mid route, we must be sure we can back up our logic and reasoning for doing so with confidence in our decisions.

I hope you find the above information useful. I’ve tried to keep it as basic and uncomplicated as possible. If you are extremely familiar with the above information, then I recommend taking your understanding a step further as part of your ongoing development of mountain knowledge.