The weather in Venice in early October is typically like the weather in SF has been the past few days; cool, in the 60's, comfortable, but wear a long sleeve knit and a light jacket. During the day you usually have to take the jacket off because it may get hot. Maybe it will be a little colder in Venice. Just as in SF, it's unpredictable, but it's not going to be brutal either way.

There is a huge seasonal difference when it comes to visiting Venice. With the heat, mosquitos, and crowds during late May, June, July, August and early September it can be a torturous, "I'm never going back there again," experience.

Mid-October starts to get more pleasant. There is still some crowding but it is not at all like it is during the highest season. From then on it gets progressively better, even though cruise ships keep coming in until mid-November. From mid-November until mid-March it can be pretty cold. That's a great time to visit, but that's another issue.

June through September are out of bounds in terms of tourists and weather.

The risk of a combo of wind and cold is pretty low in October, but it is as unpredictable as the weather is anywhere. I've been there in late October when a storm made it brutal, but by the evening I was walking around with nothing but a light sweater and a windbreaker. It's like visiting NYC in October; it may have mild, early fall weather, or it can be capriciously cold. It's unpredictable, but you won't freeze.

I wouldn't bother with tidal charts for aqua alta. You can predict the tides, but the wind and daily temperature play a huge part in the weather and water level, and no one knows what they will be months in advance when buying plane tickets.

In fact, I would't bother myself about aqua alta at all. The photos of high water are interesting shots by photographers, but look at peoples' faces; they are usually smiling, or wondrous, as if they are in a museum. High water means the weather is not cold. It is a treat, unless you have to get to school or work and the only way there is on the passerelle, blocked by tourists. You won't get wet if you don't want to, and it is a great opportunity for unforgettable photos.

The trade offs for going in October outweigh any other considerations, because the weather is usually just fine. With a few layers you won't really need a winter coat. However, mid-November through early March can be pretty cold.

In my opinion, everything said here is more or less the same for April, except the weather may be a little better.

You will also love Salzburg. A snowy day in Salzburg is magical. These are two terrific cities to visit.