I'm planning a new saga for my group, inspired by the Northern Winds covenant (I'm eagerly awaiting my copy of Through the Aegis from amazon) but based in the Mediterranean, and my magus will have MMF Weather. I've been trying to do some research on weather conditions of the Sea, but am not finding a great deal of info
Reading C&G, along with my limited research, I am getting the impression that the weather is relatively gentle, even in winter. So regarding auram guidelines, I would assume everyday winter weather wouldn't really push past 'normal weather phenomenon'? Only story events could potentially throw severe or very severe weather at the characters?
the weather in Mediterranée is generaly soft with little or no wind and very small waves if any. BUT suddenly (rarely but very fast change of weather) the sea became huge, the wind blows very hard and change of direction very often.
As said, weather is soft in Mediterranean sea... but when a storm is coming... it can become very dangerous... I remember being on a cruise boat during a big tempest between Naples and Corse... waves around 10 meters high... can be terrible for a sailing medieval boat...
In general, from a lot of personal experience, weather in the Mediterrenean is quite nice, even in winter. I would not hesitate sailing it, in any season, even with a relatively small (20'-30') boat. There is the occasional squall or thunderstorm, particularly in summer/fall (I've seen way more thunderstorms in the Mediterranean than in the British Isles, for example), but if you are at sea and reasonably away from the coast, it's just an inconvenience that will leave you soaked to the bone and little more.
There is one fundamental exception: the Mediterranean is full of crannies and nooks, so to speak, that can concentrate the wind, the waves and/or the currents and make them behave strangely and nastily at a given point, even when they are no trouble at all just a dozen miles away. This is typical in narrow straits, the most (in)famous probably being that between the Sicily and the southern tip of Italy, which can be so treacherous that in mythology it was the lair/battleground of two sea-monsters, Scylla and Charybdis. If you find yourself in one of these "tight spots" (quite literally) at the wrong time and with the wrong luck, you do have a fair risk of getting smashed against a rocky shore. In Ars Magica terms, these are probably supernatural creatures flexing their muscles!
But to answer the original question: no, you can't discount violent phenomena. You will encounter lightning, for example. You will encounter whirlwinds and thunderstorms. They are just not nearly as bad as what you get in the Atlantic. 10 meter-tall waves, for example, are something I have never seen in the Mediterranean, despite what Lady Merlina said. I think of the Mediterrenean as one of those little dogs that are generally cuddly, but if riled up can get all of a sudden all barks and bites, but even then due to their size don't quite manage to pack a lot of punch (though they could bite off a finger, for example)!
