Area Climatology — Page 433, Lesson 403

I want to walk you through the area climatology of the Mediterranean region, starting with some important local winds and then moving into the winter and summer patterns. Let's begin with the Khamsin. This wind is similar to the Sirocco we covered earlier, but it occurs further east. The Khamsin originates in Northern Sudan, then blows from the south through Egypt, and can affect Jordan, Syria, and Cyprus. One critical thing to note is that dust from this wind can be carried up to 10,000 feet — that's a significant altitude for dust transport. Next we have the Vandevale. This is a strong southwesterly to westerly wind that occurs specifically in the Straits of Gibraltar. It blows ahead of a polar front cold front that's approaching from the Atlantic. The Vandevale is described as very squally — meaning it has sudden, violent gusts — and it brings much low cloud with it. Now let's look at upper winds in the region. In the extreme west of the Mediterranean area, a few polar front jet streams occur in association with polar front lows. There's also the Subtropical jet over Morocco. This jet does not affect the western part of the sea area, but it can affect the eastern Mediterranean in the Cyprus and Egypt region. The Subtropical jet is centred at the 200 hPa level, with maximum westerly winds at over 100 knots. For icing conditions in winter: clear ice can occur in convective cloud and thunderstorms. Additionally, freezing rain — also called rain ice — can occur over Northern Italy where the freezing level may occasionally be right at the surface. Now let's move to summer conditions. Pressure systems in summer are dominated by two features. First, the Azores High — the Azores subtropical high at 35°N extends eastwards across the Mediterranean. Second, thermal lows develop: pressure over Egypt, Lebanon, and lands to the East is relatively low due to intense insolation — that's strong solar heating of the ground. For cloud and precipitation in summer: there is little cloud aside from fair weather cumulus. However, local cumulus and cumulonimbus can occur over the high ground of Greece, Italy, and Turkey due to convective and orographic uplift — that's air being forced upward by the terrain and by heating. This can possibly result in local thunderstorms. Finally, visibility in summer: dust is trapped near the surface by generally descending air, and this dust can reduce visibility across the region. In the Straits of Gibraltar specifically, warm moist air flowing out over the cooler Atlantic can produce advection fog or low stratus and stratocumulus clouds.