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Winter winds - the "katabatic" effect

Created by Bristol Bristol  > 9 months ago, 24 Jul 2012
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Bristol
Bristol

ACT

347 posts

24 Jul 2012 9:58am
A so-called "katabatic" wind occurs when cold, therefore dense, air drains down a slope. If the draining air gets squeezed between headlands, the wind generated can be quite sailable. Italy's Lake Garda is an extreme example of this.

I have found that the Clyde River at Bateman's Bay gets a regular katabatic wind. The critical triggers seem to be overnight frosts on the tablelands, and calm conditions at "the Bay".

To take advantage of this phenomenon, you have to be rigged and ready to sail not long after sun up. You can rig big; the wind probably will not exceed 15 knots. The wind will dissipate after about an hour; be prepared to wallow back to shore. The wind will be "offshore", so discretion is required. Early morning is shark feeding time; plenty of incentive to make those gybes!

There are probably lots of places in southern Australia where katabatic winter winds occur. What is "unnatural" is to consider that there's local sailable wind to be had early in the morning, when, so often, the BOM forecast suggests nothing sailable for the entire day.

Good luck in your quest.
FiremanSam
FiremanSam

VIC

148 posts

24 Jul 2012 10:00am
I always thought Anabatic (spelling?) and Katabatic winds occured at dawn / dusk ?
Davage
Davage

VIC

182 posts

24 Jul 2012 12:32pm



Davage
Davage

VIC

182 posts

24 Jul 2012 12:36pm
Select to expand quote
FiremanSam said...

I always thought Anabatic (spelling?) and Katabatic winds occured at dawn / dusk ?


I was taught the same thing, but was for summer/fire season conditions.
We used to remember by-the cool cat comes out to play at night.
sboardcrazy
sboardcrazy

NSW

8292 posts

24 Jul 2012 12:44pm
Select to expand quote
Bristol said...

A so-called "katabatic" wind occurs when cold, therefore dense, air drains down a slope. If the draining air gets squeezed between headlands, the wind generated can be quite sailable. Italy's Lake Garda is an extreme example of this.

I have found that the Clyde River at Bateman's Bay gets a regular katabatic wind. The critical triggers seem to be overnight frosts on the tablelands, and calm conditions at "the Bay".

To take advantage of this phenomenon, you have to be rigged and ready to sail not long after sun up. You can rig big; the wind probably will not exceed 15 knots. The wind will dissipate after about an hour; be prepared to wallow back to shore. The wind will be "offshore", so discretion is required. Early morning is shark feeding time; plenty of incentive to make those gybes!

There are probably lots of places in southern Australia where katabatic winter winds occur. What is "unnatural" is to consider that there's local sailable wind to be had early in the morning, when, so often, the BOM forecast suggests nothing sailable for the entire day.

Good luck in your quest.

Years ago we sailed our boat down the East Coast in June.We'd get up predawn and set sail in those W's and have a great sail in the morning in perfectly flat water close to the coast. By midday we'd be in a port and spend the afternoon walking around exploring.You had to rug up but it was perfect sailing!
We got from Sydney to Eden that way and then a SW front came in so we turned around and set off home.
FiremanSam
FiremanSam

VIC

148 posts

24 Jul 2012 3:41pm
Select to expand quote
Davage said...

FiremanSam said...

I always thought Anabatic (spelling?) and Katabatic winds occured at dawn / dusk ?


I was taught the same thing, but was for summer/fire season conditions.
We used to remember by-the cool cat comes out to play at night.


That explains it Davage... I was doing Wildfire Crew Leader at the time !

lol
dan berry
dan berry

WA

2562 posts

25 Jul 2012 6:28am
I always thought it was like a reverse seabreeze in winter due to the early morning heat differential between the land and sea?
buzzy
buzzy

TAS

2433 posts

25 Jul 2012 10:56am
From BOM 'Land Breeze'
'A local offshore wind. At night, when the land cools more quickly, and to a greater extent, than the sea, the land breeze circulation is set up.

Cooler air from the land flows offshore to replace the warm air rising over the sea.

The air in contact with the sea warms and expands and the resulting changes in the pressure and temperature differences and distributions cause the land breeze circulation.'

Other references state that it can be any large body of water such as a lake etc.

We get these in Hobart regularly in winter, along with fog and mist coming down the Derwent river. Normally about 0-2 degrees and wind chill making it seem well under 0 degree. Wind ranges 12-20 knots, water is slightly choppy and my car and office heater is so much more appealing.

Katabatic wind, again from BOM
'Downslope wind caused by greater air density on the slope than at some distance, horizontally from it. The wind is associated with surface cooling of the slope.'

Dont like my chances of sailing down a slope.
xarvia
xarvia

TAS

145 posts

25 Jul 2012 11:01am
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buzzy said...


Dont like my chances of sailing down a slope.


I thought you'd be up for a bit of this?!?



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