Wednesday, July 13, 2016

Alpine Lee Cyclone Wreaking Havoc on Tour de France

Spoiler Alert: If you don't want to know what happened in today's (Wed 13 July) stage 11, read no further.

Strong winds wreaked havoc on the Tour de France today, with the Peter Sagan (stage win) and Chris Froome (putting time on rivals) taking advantage.

The weather is also expected to wreak havoc tomorrow and it has already been announced that the stage up Mt. Ventoux will stop at Chalet Reynard, about 500 vertical meters below the summit.

The culprit is a strong Alpine lee cyclone that has developed on the south side of the Alps.  The 6-hour GFS forecast valid at 1200 UTC today (around the time of Stage 11) shows the classic signature that one sees when a cold front impinges on the Alps, stalls on the north slopes due to topographic blocking, and a variety of processes contribute to cyclogenesis to the lee near or over the Gulf of Genoa.

The strong pressure gradient drives the strong Mistral (northwest) winds that affected Stage 11.

For tomorrows stage 12, the main surface low has moved off into northern Europe, but the trailing cold front remains stalled over the north slopes of the Alps and an intense lee trough remains on the south side.

Mt. Ventoux will surely be buffeted by strong winds.  It may just south enough to avoid precipitation, but I wouldn't be surprised if there was some rain.  Expect the unexpected.

It's a shame that the climb will be shortened, but it could be an interesting stage nonetheless.

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