During the approach to the mountain, as dawn is breaking, watching the sky on the eve of an important ascent — or of a less demanding hike — is surely the gesture that every mountaineer has made and always will make, in the hope that the dawn heralds fine weather. Unfortunately it often doesn't.
The success of a hike depends largely on favourable weather. Many of the tragedies that happen in the mountains are due to adverse weather conditions, and to mountains tackled light-heartedly or with poor knowledge of even the most elementary notions of climate.
Every mountaineer or hiker should have a minimum store of meteorological knowledge that lets them forecast, at least roughly, how the weather will develop. Instead, all too often we settle for a hurried glance at the forecast in the newspaper, perhaps a national edition, or at the weather page of the local TV.
The weather in the mountains is very well described on meteomont.it, a tool that keeps the mountaineer thoroughly informed. The mountaineer, however, must have in his cultural baggage a minimum of empirical knowledge of certain natural clues: the sky can give all enthusiasts the basic elements for reading the unmistakable signals that the sky and nature give, for good and for ill.
Weather conditions
Settled fine weather
The barometer shows high pressure, the temperature is low in winter and warm in summer. Blue or light grey sky at dawn. Fog and haze in the valleys.
Note: the thick fog in the valley, which is so annoying in the morning as you arrive by car, is a guarantee of clear skies higher up.
The clouds are thin and transparent and disappear in the evening.
Changeable, tending to improve
Humidity drops, the temperature falls in winter and rises in summer. In the morning an overcast sky with a grey dawn. At sunset clear, with a red colour. The horizon clears of clouds, the cloud layer shows the first breaks of clear sky.
Changeable, tending to worsen
Falling pressure. Rising humidity. The temperature rises in winter and falls in summer. Up high you see the blue of the sky give way to a pale blue/white, while from the plain the white is sharper.
You see haloes around the sun and the moon, as a sign of rising humidity. Red-orange sky at dawn. Medium-high clouds can be seen approaching from the south, south-west and south-east. At sunset the horizon is covered with masses of cloud.
Bad weather
High humidity. Low pressure. Temperature falling in summer, rising in winter. The sky, if visible, looks pale blue, red at dawn. The clouds, if they break, show other clouds above them.
Natural signs worth recognising
Haloes around the sun or the moon
If the edge of the disc — especially on the moon — is clearly visible: low-to-medium water clouds, the weather holds.
If the edge is not visible, within 6–8 hours stratified clouds will arrive: the weather is getting worse.
Aircraft contrails
If a contrail forms, the temperature at high altitude is very low. If the contrails persist for a long time and spread out, there is a high water vapour content in the atmosphere: it is a sign of the weather worsening in the following hours.
Useful resources
- Weather forecasts specifically for the mountains: meteomont.it (Italian Air Force Meteorological Service)
- Snow bulletins and avalanche danger: aineva.it