Any Meteorologists Out There?

[Gardian]

Strange phenomenom around here.

For most of the day, it can be quite still: no wind to speak of. Then, around 17.00, we'll get quite a breeze spring up for maybe an hour, always from the west.  Our neighbour remarked on it shortly after we moved in and we thought that it was just one of those 'old wives tales' - but of course, he was absolutely right. Other than when the Mistral is blowing (which is in truth, relatively rare and when it does, it supplants anything else), this occurs more or less daily.

Has anybody got any idea how / why this should happen? 

[Suze01]

Where we live, the day is often at it's hottest between 5 and 7pm.  Maybe the rise in temperature causes the wind to increase (insert: little smiley with a Gallic shrug!)

[andyh4]

Ian,

since you are in Gard, it is almost certainly to do with differential temperatures between coastal land, the sea and the mountains.  Not knowing your exact location I cannot be certain of the main influence.

The sea temperatures remain relatively static, whereas the land tempertures warm up during the day and cool down at night.  The differntial in temperatures causes differences in air density and nature tries to even these out = wind.

Mountains have differential temperatures also, so that under equal conditions the lower more level slopes heat up more than the steeper summits.  The colder air at the top then eventually overcomes the slowly rising warm convectional air and cascades downwards = wind.

 

Since you say the wind is a westerly I am guessing the mountain effect is playing the greater role.

 

In the UK I had a similar experience in the Vale of York where around 4pm the wind would suddenly pick up on a still day.  Great for sailing.

[Mpprh]

[quote user="Ian Horn"]

Strange phenomenom around here.

For most of the day, it can be quite still: no wind to speak of. Then, around 17.00, we'll get quite a breeze spring up for maybe an hour, always from the west.  Our neighbour remarked on it shortly after we moved in and we thought that it was just one of those 'old wives tales' - but of course, he was absolutely right. Other than when the Mistral is blowing (which is in truth, relatively rare and when it does, it supplants anything else), this occurs more or less daily.

Has anybody got any idea how / why this should happen? 

[/quote]

Hi

I live close to you, and sail out of Port Camargue.

I think this must be a local effect distorted by hills and valleys ? The land / sea winds are normally North - South. 

Frequently, the coast experiences a 180 degree shift during the day : North wind in the morning, lull at lunchtime, then an increasing South wind until the sun goes down. In the afternoons, sailors keep close inshore to take advantage of the stronger winds being sucked in towards the warmer land.

This image http://www.the-languedoc-page.com/photos/languedoc-photo-208.htm was taken in the afternoon, and shows a sailing boat off Ste Marie de la Mer. It is heading West, with a gentle south wind in the sails.

East - West winds are relatively rare here, but not in Rousillon !

Peter

 

 

[Gardian]

Many thanks to all: even to a complete layman like me, that starts to make sense.

We're in the NE of the Gard, with the Cevennes to the west / north west (though some 50kms away) and the Ardeche Gorge to the N / NW.  I think that I'll pass on trying to explain all that to my neighbour though!

[andyh4]

OK with that extra info Ian, your wind (not yours personally) is being driven by the Cevennes.

Peter's is driven by the classic on-shore/off-shore effect.