Weather in the Dolomites
Mountain sports of all types are incredibly dependent on the weather. Not understanding what is likely to happen during the day ahead can lead to poor decisions, potentially posing a serious threat to your life due to various factors. I firmly believe it is everyone’s duty of care to themselves to understand the conditions they might encounter in the Dolomites, whether walking, biking, skiing, or climbing.
Over nearly 30 years of visiting the Dolomites, I’ve witnessed the weather change on a dime many times. From snowfalls and hailstorms in August to temperatures rising from -5ºC to +10ºC in the middle of winter overnight. Each of these scenarios deserves consideration and presents its own dangers, which might be less obvious to the less experienced.
The fundamentals of weather in the Dolomites
The orientation and location of the Dolomites are crucial for understanding the weather systems they experience. Let’s begin by examining the distances involved and the role of the rest of the Alps.
The Alps form a formidable wall of mountains, ranging from 2,000 to 4,806 meters in height above sea level, curling around Northern Italy. This creates a significant barrier to air masses moving across Europe. The Dolomites, located on the southern edge of this range, lie to the north of the Adriatic Sea in a particularly wide section, spanning approximately 150-200 km. The Alps generally run east to west, with only the westernmost part curling around.
As a result, air must either circumvent the mountains or be forced rapidly upward over the barrier, causing dramatic cooling. Typically, there is a temperature drop of 30-40 degrees Celsius from sea level to the summits, following the approximate rule of thumb that there is a 1ºC drop per 100 meters of elevation.
Additionally, it’s important to note that the Po Valley to the south forms a low-altitude floodplain that spans the entirety of Italy. To the north, the land is also relatively flat, with a few minor ranges in the west.
This shape dictates that to the south, weather can become trapped in the shadow of the mountains, practically guaranteeing that it is forced upwards. This has a huge impact on the weather. It also dictates that the patterns which will cause adverse weather form in predominantly two ways which we’ll analyse below.
Alpine Maritime systems
The Dolomites often experience an Alpine Maritime weather system due to their proximity to the Mediterranean Sea. The weather systems travel across a significant expanse of open water, where the heat in the air facilitates the evaporation of water, influencing the weather patterns in the mountains. Especially during winter the jet-stream plays a crucial role in bringing this weather to the area, dictating where landfall is made. Its orientation can significantly affect how far east or west the weather systems approach the Alps. Consequently, even a minor change in the jet-stream can lead to major changes in the weather experienced in the Dolomites, making it very difficult to predict exactly what the weather will do.
As the air arrives, hot after crossing Northern Africa, it absorbs more moisture over the sea, increasing the likelihood of rain in the mountains. When this moist air is rapidly forced to ascend due to the significant elevation gain, it often results in violent rain and thunderstorms during the summer, whilst in winter, this process brings heavy snowfall.
Summer AM Systems
These weather systems are extremely common during the summer when the jet stream is generally farther from the equator. The mountains create a barrier that traps a pool of warm, humid air, which cannot escape. Thunderstorms are particularly frequent in July and August. As the heat builds during the day, the humid air rises, and the wind pushes it over the mountains. This process forms cumulonimbus clouds, leading to storms over the mountains. Predicting the exact time and location of these storms is challenging due to the complex topography, meaning conditions can vary significantly from one valley to the next.
So, what do I use as a rule of thumb? If the air temperature reaches 25ºC or more by around 10 am at 1200m ASM, it’s likely to rain at some point during the day. Typically, this rain arrives between 2 and 4 pm, with downpours lasting one to two hours before clearing up, leading to a sunny late afternoon and evening.
Weather forecasting services often show rain across the mountains all day because they struggle to predict it accurately due to the topography and the nature of the wind and humidity levels. I find that my approach works quite well, combined with an optimistic attitude. Always pack waterproofs, and you won’t go far wrong. If the conditions are as described, include waterproof trousers and aim to be at a hut or some form of shelter around that time. Plan a break, and then you can continue once the rain fades.
The above gallery shows the progression from a pretty reasonable day, to an electrical storm. Starting from Passo Valparolla, we climbed the Kaiserjaegersteig to the summit of Lagazuoi. The third image is shortly before the summit, the last is as we were running to get off the ridgeline and into the Lagazuoi tunnels before the storm hit.
Winter AM Systems
In winter these systems manifest slightly differently and are largely reliant on the Jet-stream. The path of these high altitude winds alters significantly, snaking around the northern hemisphere and often gets set in a pattern for part or all of a season. Exactly where this path runs will change the direction from which warm moist air arrives. If the jet stream loops over north Africa, it will be heated by the Sahara desert, before picking up moisture over the Mediterranean and delivering warm wet air to the mountains where it falls as heavy snow.
This weather system has become increasingly rare over the last decade. But if you watch a jet stream forecast over the weeks before your trip, you should be able to see the required conditions for snow arriving quite clearly. Of course it can be temperamental, but hopefully this can be of some use.
European Continental systems
Another scenario occurs when the weather comes from the north or northwest, across northern Europe and the Austrian Alps. This creates a very different picture. The Alps in this area are particularly wide, spanning 150-200 km, which means any precipitation is likely to fall on the northern side, in Germany and Austria. As the air crosses the Alps, it loses its moisture, resulting in very dry and warmer air due to recompression and solar heating. This dry, warm air, known as a Föhn, is common across the Alps, especially in this region.
The Föhn wind is so warm and dry that it actively absorbs moisture from the surface, melting snow and creating a wet, avalanche-prone snowpack. It can remove vast amounts of snow, strip hillsides, and cause the snowpack to become extremely icy when it refreezes. Combined with the wind conditions, this can create a very uneven and challenging surface for skiing. Refer to the photo at the start of the article to see what these conditions might look like.
In summer, these conditions are less problematic and can even be favorable for walking.
These conditions are caused by warm, wet air arriving on the jet stream from the northwest Atlantic. If you see a forecast showing the jet stream crossing France and moving down into Italy, you can be sure these will be the most likely conditions you will encounter.
A summary of the prevalent weather
We’ve discussed in some detail so lets talk month by month about what you’re likely to see. Remember, none of this is hard and fast and there will be yearly variations.
Below you will find a data chart to give you some idea of how the weather varies. These are average figures for Malga Ciapela which is a mid height ski base station. On the mountain you can count 1degree cooler for every 100m height gain and higher levels of rainfall and wind – see the data for the summit of Marmolada for an idea of how it might vary. But remember that these are long standing averages and anecdotally, I’d say that December and January have become less snowy, with more falling during March than previously.
However the general trend is for high rainfall during June, July and August, along with the highest temperatures.
Which forecast should I use?
Forecasting weather in mountain ranges, especially the Dolomites, can be quite challenging. Many people wonder if they should change their plans based on a poor forecast. Generally, unless there’s a prolonged weather system bringing heavy and continuous rain, I would advise against it.
A mountain guide once told me, “The best way to know the weather is to stick your head in the clouds.” Essentially, if the weather looks promising, go and see for yourself. Even if the day doesn’t turn out as expected, you’ll still gain something valuable from your time in the mountains. Over the past 30 years, this advice has proven true countless times.
Here’s my suggestion: follow the rule of thumb mentioned above and keep an eye on the jet-stream forecast to spot any unusual trends. For more detailed weather trends, you can check the following sites:
These resources, while basic, are often accurate in terms of trends and can help you decide whether to stick with your plans or reconsider.
A word about storms
As mentioned, during the summer, the Dolomites are renowned for severe storms. These can be extremely dangerous in the following ways:
- Exposure (i.e. cold) – Ensure that you are carrying waterproof coats as an absolute minimum. When in the mountains, a peaked visor or hat can help keep rain out of your eyes so that you remain mobile even in the heaviest downpours. In the high mountains you should also consider taking waterproof trousers with full length zips down the leg so they can easily be pulled on over your boots without the need to remove them. You should also consider carrying a synthetic (not down) insulative layer. Although Down is warm, light and compact, it becomes useless when wet. Think about Primaloft or similar.
- Lightening strikes – when you are high up in the mountains, the chances that you will be hit by lightening become exponentially higher. The higher you are, the more likely and the best solution is to go down. If caught by a storm, you should be looking to descend as fast as humanely possible even if that means going up slightly to access an easy path down. Keep your wits about you, remain calm and make good decisions
- Find shelter ASAP – huts are there for shelter. Use them. Any metallic structure which you can get inside will be safe, eg cable car stations
- Remember that as a rule of thumb, once you are 1/3 of the height gain, valley floor to summit, the danger reduces massively as you are effectively in a shadow.
- You can identify when a storm is likely to hit as you will notice windy updrafts happening. Once you notice this, you know that it is imminent within the next 20-30 minutes.
- Do not shelter beneath the lip of an overhang. Water falling from the lip provides the perfect bridge to allow the electricity to ground – don’t get in the way. If you find a cave or old dug out, get right inside.