Mistral Wind
For those of you who are curious, I learned some more about the Mistral wind that was blowing so VERY strong when I was in Avignon.
The mistral is a strong, cold northwesterly wind system that blows from Southern France into the Gulf of Lions. Although strongest in the Gulf of Lions, with sustained winds often exceeding 40 kt, and gusts sometimes to 100 kt, its effects are often felt past Sicily into the eastern portion of the Mediterranean basin. Wave heights associated with the mistral are commonly 15-20 ft (4.5-6.0 m) and have sometimes reached a maximum height about 30 ft (9 m). The mistral is most common in winter and in spring with the strongest episodes tending to occur in the transition between those two seasons. Duration of effects with winds exceeding 30 kt for over 65 hours have been reported at some locations.
It is an example of a katabatic wind, which is caused by air that is cooled over the mountains by the presence of a high pressure system or radiative cooling. In the case of the Mistral, air is cooled above the Massif Central, the central plateau of France, and the Pyrenees. It then flows down into the Garonne valley, because its density is higher than that of the surrounding air. The presence of Garonne and Rhône valley creates a funnel effect, speeding up the current towards the Gulf.
A favored sequence for mistral development is passage of a cold front into the Gulf in advance of a short wave trough at upper levels. The upper- level trough produces southwesterly flow aloft and positive vorticity advection over the position of the cold front in the Gulf. This pattern leads to cyclogenesis in the Gulf of Genoa. As the upper level trough advances so that northerly winds aloft are in phase with the northerly surface flow over Southern France, strong mistral winds occur.
The mistral is a strong, cold northwesterly wind system that blows from Southern France into the Gulf of Lions. Although strongest in the Gulf of Lions, with sustained winds often exceeding 40 kt, and gusts sometimes to 100 kt, its effects are often felt past Sicily into the eastern portion of the Mediterranean basin. Wave heights associated with the mistral are commonly 15-20 ft (4.5-6.0 m) and have sometimes reached a maximum height about 30 ft (9 m). The mistral is most common in winter and in spring with the strongest episodes tending to occur in the transition between those two seasons. Duration of effects with winds exceeding 30 kt for over 65 hours have been reported at some locations.
It is an example of a katabatic wind, which is caused by air that is cooled over the mountains by the presence of a high pressure system or radiative cooling. In the case of the Mistral, air is cooled above the Massif Central, the central plateau of France, and the Pyrenees. It then flows down into the Garonne valley, because its density is higher than that of the surrounding air. The presence of Garonne and Rhône valley creates a funnel effect, speeding up the current towards the Gulf.
A favored sequence for mistral development is passage of a cold front into the Gulf in advance of a short wave trough at upper levels. The upper- level trough produces southwesterly flow aloft and positive vorticity advection over the position of the cold front in the Gulf. This pattern leads to cyclogenesis in the Gulf of Genoa. As the upper level trough advances so that northerly winds aloft are in phase with the northerly surface flow over Southern France, strong mistral winds occur.
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