Geneva lake winds

I had a break in trainings - I am back in Geneva, but the wind is gone! And you need wind to sail, right? Well, Lac Lemain is famous for its capricious winds, so in fact you need a good knowledge of wind patterns - after knowing how to sail fast, this is probably the biggest success factor. So I thought this is a good opportunity to look into the Geneva lake winds.

Les sauveteurs du Leman (SISL) gives a good overview of the regional winds. Let's look into those that you have probably heard: La Bise, Le Sechard et le Joran.

La bise is the most famous one, especially after it sinks some boats in winter and produces images like this (after Didier Ulrich's blog):

It is a regular, cold N-NE wind caused by a system of high pressure over the British islands and lower pressure over the Mediterranean. It builds up after the passage of a cold front and predicts good weather. The legend has it that it blows for 3, 6 or 9 days, but it does not seem to be true, as a Bise of 1-2 days are more common (Wikipedia) . Here are its typical directions across the lake (after SISL):

A good Bise is a 6-7 Beaufort strong; it is the only wind appreciated by the local wind- and kyte-surfers. But "une petite Bise" can be as week as 2 Beaufort.

Le Sechard is the other term that I heard sailors use with a knowing grin. I found it confusing, as the directions are not that different from Bise (at least on the Petit Lac):

I've read somewhere that it is a foehn wind. This confuses me even more - shouldn't a foehn wind blow from the mountains rather than along the mountains? Looking at this archive comment from Alinghi, I think I am not the only one to be confused.

I notice the following five differences. Le Sechard is not as strong as la Bise (probably 1-3 Beaufort), it is warm, it turns into ENS as you go into the Grand Lac, it is not nearly as regular and it dies before the sun set.

The differences with Le Joran are quite clear. This one is a gusty NW wind blowing from the Jura (hence its name).

It often comes with a changing weather and can turn into a storm, which explains its bad reputation. I think we had the Joran during the 3H de Versoix regatta - remember the gusts and marks not aligned with the wind, so that all the legs were beam-reach?

Let me finish this post with a quiz. Looking at this wind map for Thursday and the following barometric map of Europe (copied from WindFinder) and knowing that very similar winds are predicted for the whole of Thursday (including well into the night), which of the three winds described above can we expect for this Thursday training?

If this subject interests you, please also send me your favourite weather links - maybe we can build something useful for the YCC.

For completeness, I found this wind map interesting. Thanks for reading! Michał