Local Winds and Weather — Page 412, Lesson 373

I want to walk you through a set of local winds that you’ll need to know for your ATPL meteorology syllabus. We’re starting with valley winds, and the classic example is the Mistral. A valley wind is simply air that gets funnelled through a mountain gap or down a valley. The Mistral is a textbook case: it blows down the Rhône Valley, which sits between the Massif Central and the Alps, all the way to the French Mediterranean coast and beyond. It’s usually a winter wind. The driving pressure pattern is high pressure over Central France and low pressure over the Gulf of Genoa. Temperatures during a winter Mistral are well below zero — we’re talking serious cold. Flying conditions are turbulent, and the winds are strong, typically 40 to 75 knots. Next is the Bora. This one is part valley wind and part katabatic wind — a katabatic wind being a gravity-driven flow of cold dense air down a slope. As you can see in Figure 21.4, the Bora blows down the north Adriatic. The pressure setup is high pressure over Central Europe and the Balkans, with a low over the Adriatic. The wind speed is around 70 knots, with great gusts exceeding 100 knots in places. The Bora is strongest and most frequent in winter. One important note for your exam: EASA examines the Bora as a katabatic wind, so remember that classification. Now we move to the Mediterranean winds: the Sirocco, the Ghibli, and the Khamsin. All three are similar in that they blow ahead of frontal depressions tracking along the North African coastline. The Sirocco blows over Algeria. It is a hot and dusty southerly wind coming out of the desert. It’s usually a springtime wind and may last a day or so. Visibility can be reduced to below fog limits — that’s below 1000 metres. The Sirocco may travel as far as the French coast, and as it crosses the sea it can pick up moisture, producing low stratus, drizzle, and fog. The Ghibli is a similar wind that blows over Libya — same general character, hot and dusty from the desert ahead of a depression. The Khamsin blows ahead of depressions tracking along the Mediterranean coast of Egypt. Conditions are similar to the Sirocco and the Ghibli. The name Khamsin is also given to south or southwest gales blowing in the Red Sea. Finally, we have a squall wind from South America: the Pampero. This is a severe windstorm that blows around the estuary of the River Plate, between Uruguay and Argentina. It is a cold, dusty south to southwest wind that blows behind a cold frontal depression. Stormy, gusty conditions prevail, with a considerable temperature fall after the storm passes. The squall itself is short lived, but the strong, steady wind may last for some hours. Pamperos usually blow in spring and summer. That covers the key local winds in this section. Let me know if you have any questions on any of them.