Mountain Weather

Mountains attract their own weather and it is often different from that experienced in the lowlands nearby. 

Checking the weather forecast is an essential part of planning a trip to the mountains and you should pay particular attention to the following:

Wind – Wind speeds in the mountains can be much greater than that at sea level. As the ground rises the air is forced upwards and is squeezed over mountain tops, up valleys and between gaps in the hills (saddles).

Particular notice should be taken when strong winds are forecast, winds over 60km/hour are very serious (see image below) and can make progress very difficult and tiring, with an increasing risk of being blown off your feet.

Strong winds can lead to a significant wind chill, where the temperature feels much colder than it is, notice the wind chill of -1 C on the image below. This is a major risk factor in the onset of hypothermia (see below).

Temperature – We know that it is colder at higher altitudes and in the big mountain ranges, but temperatures can decrease significantly with increased height in relatively modest mountains too. Temperatures decreasing with height gain is called the lapse rate, and in the more temperate latitudes this is approximately 1.0C for every 100 metres of height gain.

So at 1000m it could be 10.0C cooler than at sea level and may well be below freezing on the mountain tops, resulting in sleet, snow and frozen ground, all significant hazards to be aware of.

Temperatures just above freezing, in combination with rain or sleet and a strong wind, will bring an increased risk of hypothermia. This is a serious condition where the core temperature of the human body drops below 35 C, which can result in shivering, impaired motor skills and cognitive decline, and ultimately death.

Precipitation – As saturated air is forced upwards over the mountains the moisture it contains will condense, forming tiny water droplets in the form of clouds. Clouds can form at relatively low altitudes, and when the droplets coalesce, they will fall as rain.

Clouds and rain will reduce visibility, make navigation more challenging, and if you don’t have effective waterproof clothing, can make you wet and cold with an increased risk of hypothermia.

In certain circumstances the clouds can contain strong convection currents and the water droplets can be swept upwards to freeze at high altitude only to fall again as hail. In very cold conditions the water vapour in the air will crystalize directly onto particles of dust and fall as snow.

In summary, always check the weather forecast before you head into the mountains and make sure you have the appropriate clothing and equipment to deal with the predicted conditions. Never be afraid to turn back if the weather is worse than you expected.

Russ Mills is the owner of Mountaintrails.ie a guiding hiking and mountain training business based in Dublin.