I have a bit of wind

Danny_Labrador

Danny_Labrador

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You guys know more than I do.

It’s windy!

There is something that I cannot understand.

At dawn today when I let the humans out it was perfectly calm.

Dark but calm. 20 minutes later it’s was windy again, (very). Why the cessation at dawn? I’ve noticed this before.

weather.jpg



The weather system is still there that's causing the wind. Why does it often stop around dawn?
 
Can i download this as well??

The reasons simple! Sailing at nights just fantastic!!!Better still if it dose start howling you dont see the sea so clearly and the waves that plopf aboard are luminous and lovely looking!
 
It's Gods little joke. He does this just when you get up and have brekkie to get you to sail out of your nice sheltered harbour and then gives you both barrels.....
 
Danny

Dunno if this will fully answer your question, but the "diurnal effect" is quite significant in most conditions. This is where the lack of surface heating overnight stops turbulence in the lower 2000 feet or so of atmosphere.

Therefore the gradient wind, ie at 2000 feet, undisturbed by the surface, remains flowing at full speed but its energy is not brought down to the surface by daytime heating turbulence.

The normally reduced surface windspeed is due to surface friction overland, not so much over the sea, where the surface wind matches more closely that at 2000 feet.

All synoptic chart isobars represent the 2000 foot "gradient wind" and may not be felt at the surface, or in the lee of some hills etc.

Hope this helps, it is tricky to explain and a forecaster would explain it better. Much of it depends where you are, and what the local topography is like, and how much heating there is.

Pops
 
Thanks neat answer , but why the almost switching on and off effect at dawn and dusk, surely the atmosphere cant react that quickly. Not being a smart ass just this has puzzled me for ages and this is the first answer that logically answers most of it
Thanks
Keith
 
More thoughts,
Suns heating etc is in East-West whereass prevailing wind etc West-East
therefore there will be no reserve(residual,stored) heat.
Hope I didn't just say where asss doesn't look right does it.
Happies
Keith
 
The switching off effect - I don't think there is any good prediction or explanation for what is probably a co-incidental collection of "things going on".

Free and predictable air flow doesn't ever really happen on land, there are too many variables. Even a 10 degree shift in direction could cause a local calm spot, especially if there's any land or sea breeze contributing, which in itself could subtract from a gradient component and produce an apparent lack of wind for a while.

Imagine a stream, flowing over rocks, not too deep, then drop some dye in it. Follow that dye downstream. Apart from being totally unable to predict where the dye will go, it might also collect behind stones, thin out in other areas, rise and fall throughout the depth of the river and generally be very random. Thats also similar to airflow over land areas.

Over the sea, especially way out, the airstream will be much more predictable, suffer less diurnal effect and you can usually leave your sails set for hours with no changes.

I am now at my limit of knowledge AND guesswork here!

Pops
 
There may be something in your East-West thing, but I don't think so. Surface heating only affects the area above it, and will produce turbulence in any airflow wherever it is coming from. Err, I think.

Pops
 
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