Why is it raining near fronts

Gathering weather fronts

Snow and weather

Clouds bring snow and that is mostly good news. But not all clouds are the same. Some come quickly, others creepily. This subject is too complex to learn everything about weather in this course. But you will get to know the basic information about clouds and fronts. Fronts, a typical term from meteorology, is the collective term for warm fronts, cold fronts and occlusions.

1. Warm front

With a warm front, warm air originally comes to the mountains. Since warm air is lighter than cold air, it will primarily be felt in the higher layers of the air. When the warm front comes closer, the warm air can also be felt in deeper layers of the air. The passage of a warm front does not go unnoticed. The snow line rises, although it can initially be warmer on the mountains than in the valley. The wind will turn a little towards the south, the humidity level will increase and visibility will deteriorate.

A warm front therefore brings snow, warm air, a south-turning and ever stronger wind and a rising snow line. In addition, the view becomes worse.

A warm front is easy to see on the weather map. But they are also easy to spot with the naked eye, because warming fronts can be seen from afar. The first high clouds provide some diffuse light and possibly even a special light effect (halo) around the sun. At this moment the front with precipitation is about 600 kilometers away. At the same time, the air pressure drops - you can measure this with the altitude function on your sports watch.

You can recognize warm fronts on the weather map by the red lines with semicircles on them.

You can recognize a warm front in practice by the high clouds that you can see arriving from afar.

If you see a warm front arrive in time, you often have enough time to get to safe terrain. But don't wait too long! Once the warm front has arrived, stay close to the slopes or even better on the slopes because of the poor visibility. If necessary, you can also look for powder snow between the trees.

2. Cold front

The counterpart to the warm front is the cold front. In the case of a cold front, the warm air is forcibly expelled by the cold air. This heavier, cold air is literally pushed under the warm air. This causes the warm, moist air to rise quickly. The consequences are strong cloud formation and heavy showers as well as strong gusts of wind.

You can recognize cold fronts on the weather maps by the blue lines with triangles on them.

The cold front can arrive without a clear sign for you, the temperature and the snow line drop.

You hardly notice the arrival of a cold front. It picks up quickly, which is why you are almost always too late to react on the terrain. However, cold fronts can be seen very well on weather maps and are always announced in weather reports. Due to the poor visibility, stay near slopes or better still on the slopes or look for powder snow between the trees. Even after the cold front has passed, violent thunderstorms can still occur. These clouds move up quickly and can surprise you. If you know for sure that you are dealing with the remaining clouds of the cold front and risk a white-out, then just wait until the clouds are gone.

3. Occlusion

A cold front moves faster than a warm front, which is why the warm front is ultimately overtaken by the cold front. This creates a so-called occlusion front, where the cold and warm front mix and heavy precipitation can occur. The temperature differences are less intense than with a warm front, so the snow line drops a little.

The arrival of an occlusion front initially looks like the arrival of a warm front. Don't wait too long here either! Once the occlusion front has arrived, because of the poor visibility, stay near slopes or, best of all, on the slopes. Or look for powder between the trees.

You can recognize an occlusion on the weather maps by the purple line with semicircles and triangles on it.

If the occlusion has passed, violent thunderstorms can still occur. These clouds move up quickly and can surprise you. If you know for sure that you are dealing with a residual cloud and you could get into a white-out, then just wait until the last clouds are gone. However, it would be better if you also seek protection from the trees when there is residual cloud cover in an occlusion.

4. Foehn storm

Föhn is a warm, dry fall wind that often occurs on the leeward side of mountains. We just talked about the fronts. Fronts which usually bring precipitation and which we know as "traffic jams" (if they last long enough). On the other side of the highest mountains, the so-called foehn then arises. And this can be gusty and develop quickly.

There is a traffic jam on the left side of the mountain. Foehn appears on the right-hand side.

Mountains have an obvious influence on the weather, as can be seen from the example of the foehn. You can see a mountain on the map above. Clouds on one side and beautiful weather on the other. The cloud cover has its origin in the front system of a passing low pressure area. The low pressure area literally pushes the fronts against the Alps and the air has to rise. This causes the air to expand and cool down. However, cold air can hold less moisture, which is why condensation occurs.

On cold days you will see condensation: when you breathe out, you will immediately see a small cloud of condensate forming. You don't see this on a warm day.

Condensation releases heat and liquid water. The water wants to go down because of gravity. The following applies: the stronger the traffic jam, the more intense the precipitation will be at this moment. If the cloud cover lasts long enough, it will snow or rain for a long time.

The jam can be caused by passing occlusions, warm or cold fronts. The counterpart to this is the hair dryer. The current pulls it down here and therefore does not cool down. The foehn or foehn wind is a relatively dry and warm fall wind. In addition to the difference between a wet windward side and a dry lee side, there is another notable difference, namely the temperature. From the moment the humidity on the windward side is 100%, the air temperature will drop by 0.6 degrees Celsius per 100 meters of altitude. It's very different on the lee side. Here the air sinks and warms up as it descends. The air temperature rises about 1 degree Celsius per 100 meters of altitude. As a result, you can perceive different temperatures on both sides of the mountain, at the same altitude. If you want to translate the map above into reality, pay special attention to the temperature.

Logically, currents from the south always bring with them warmer air than currents from the north. That is why the southern foehn is much better known than the northern foehn. Not only can it storm violently, the temperature can rise by 10 or even 20 degrees Celsius in a very short time. These temperatures are above zero degrees Celsius and can occur in the middle of winter. The southern foehn is therefore also a snow eater and therefore has a major impact on the snow. Fortunately, one can very well predict where this phenomenon will take place. Foehn valleys are valleys (on the lee side of a mountain) that lie in the same direction as the wind direction prevailing at that time. The valleys are initially narrow and get wider the deeper you get into the valley. The wind can accelerate to the maximum in such valleys and the air is heated to the maximum as a result.

Strong wind on the peaks!

When there is a foehn, a strong wind blows and visibility is good. Because of the sunshine you won't notice it right away, but near ridges and peaks enormous amounts of snow are transported and direct snow drifts are created.

We call this cloud over the summit a foehn fish. A sign that the wind is blowing and that the weather is worsening somewhere in the Alps.

Foehn is usually announced in the weather report, but it is also clearly visible to the naked eye. The so-called foehn fish clouds and the snow that is blown from the peaks indicate a strong foehn. That means: watch out for freshly blown snow!

5. Nice weather

There are two reasons that make the weather nice. On the one hand, there is the classic high pressure area, which can hang over the Alps for days and ensures beautiful days and cold nights. Then there is no cloud in sight. Another reason for good weather is the intermediate high. It is a temporary high pressure zone between two successive low pressure areas. In the distance you can see new clouds gathering again.

Cold, damp clouds in the valley. Sunny and warm high up in the mountains.

There are a number of things to consider when the weather is nice. First the duration of the fine weather. Do you have to reckon with a gathering front? Second, the so-called inversion. It can stay cold and humid in the valley, in which case the clouds hang down into the valley and it is cold. So first check via webcams whether it is already sunny up on the mountain. You also have to be aware that the clouds can rise, which is why you can still get white-out.

Summary
Clouds and wind are easily predictable with the help of a good weather report. Be particularly careful with an announced hair dryer or an approaching cold front. The weather can change within an hour. When planning a powder day away from the slopes, you need to take that into account.

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