Weather forecasting is not as easy as it sounds — both at sea and on land, because the atmosphere is diverse and chaotic. It’s hard to calculate.
Take for instance the fact that weather models — computer programs used to make weather forecasts, do not take local winds into account all the way through. It is because of the peculiarities of the local topography, on which many weather conditions depend — not just winds.
Now there is active work in this direction and modern high-resolution models, such as AROME, can already show local phenomena. Still, it remains a very challenging place for models. So you have to rely on your own knowledge and experience also.
Let’s learn how these three common local winds form and how do they work, namely breeze, mistral, and bora.
The most common example of local wind is a breeze. In general, a breeze is a light wind, which appears due to the temperature difference between two air masses. Breezes occur when there are a land and water boundary (e.g., the sea).
This is how it forms exactly:
- The air, which warms up above the land, becomes light and rushes up, and cooler air from the sea immediately replaces it.
- This process lasts all day, as long as there is a stream of heated air over the coast. Such a breeze is called “Daytime breeze” and can be very calm: 1–5 meters per second.
- Depending on the heating force, the land affects the circulation of the air flow. The more heating up the land, the greater the temperature difference, the stronger the breeze is.
- At night, the temperature above the land may become cooler than above the water. Then the air flows change their direction and blow from the land towards the sea. This forms the night breeze.
Breezes appear in cities and forests, too.
Their appearance is possible due to the heating of buildings by sunlight, which creates a difference in air temperature outside the city and in it. The difference can reach 8 degrees. This is enough for the cooled air to move from the suburban areas towards the city. Depending on the layout of the streets, this process can cause an increase in the wind. Most often, the air flows through wider streets.
In large forests, the temperature during the day is lower than in the fields next to them. This is because most of the solar energy is spent on the evaporation of moisture from the leaves. Because of this, during the day, a gentle wind moves from the cold forest towards the field.
In contrast to sea or forest breezes, the city breeze moves around the clock.
Read next about formation of the two other local winds: mistral and bora, in the Insaling blog — a website of a team of enthusiasts that love sea, sailing and adventure in Croatia and worldwide.
Text: Galina Konoplyannikova, a meteorologist of Windy.app and WindHub — leading pro weather forecast apps for sailing and other wind sports and outdoor activities
Editor: Ivan Kuznetsov
Cover photo: Ludomil Sawicki / Unsplash