Is there a rule of thumb for wind veering or backing with height? Reason I
ask: I often see actual wind say, bonfire smoke to differ by 60 degrees,
with cloud-over-ground movement? TIA.

Bertie Doe scrive:

Is there a rule of thumb for wind veering or backing with height? Reason
I ask: I often see actual wind say, bonfire smoke to differ by 60
degrees, with cloud-over-ground movement? TIA.

The only rule I know is that the wind at cloud height is frequently, if
not generally, from a different direction from that at ground level.
Did anyone think they were supposed to be the same?


--
Gianna
Peterhead, Scotland

On 2013-04-22 10:25:52 +0000, Bertie Doe said:

Is there a rule of thumb for wind veering or backing with height?
Reason I ask: I often see actual wind say, bonfire smoke to differ by
60 degrees, with cloud-over-ground movement? TIA.

It is probably best to read a description such as this one:-

http://www.theweatherprediction.com/habyhints/48/

"A veering wind is a wind that turns clockwise with height. An example
of a veering wind would be a southeast wind at the surface and a west
wind at 700 millibars. The wind turns in the same direction as a clock
from the surface to 700 millibars. A veering wind is associated with
warm air advection and dynamic lifting (primarily because a south wind
in the PBL transports warmer air to the north). The magnitude of warm
air advection is a function of wind speed and the pre-existing thermal
gradient. Weak winds will result in weak advection. Winds often veer
ahead of cold fronts (in the warm sector of a mid-latitude cyclone).

A backing wind is a wind that turns counter-clockwise with height. An
example of a backing wind would be a north wind at the surface with a
west wind at 700 millibars. A backing wind is associated with cold air
advection and dynamic sinking. Winds back behind cold fronts. A way to
remember the difference between the two is the memorize the set of
letters CVW and CCBC, where CVW stands for (Clockwise, Veering, Warm
air advection) and CCBC stands for (CounterClockwise, Backing, Cold air
advection)

You may wonder why a veering wind is associated with WAA and a backing
wind is associated with CAA. A veering wind turns clockwise with
height. Since warmer air is in the southern latitudes, a south wind
will promote the bringing of warmer air into the forecast region. Winds
having a southerly component at the surface and a westerly component
aloft is a veering wind. The middle and upper level winds in the
mid-latitudes will generally have a westerly component to them. The
upper level winds blow from a much more persistent direction than the
surface winds. It is primarily the surface wind direction that
determines whether the wind is backing or veering with height. A
backing wind turns counterclockwise with height. A north wind at the
surface and a westerly wind aloft is an example of a wind that is
backing. A north wind generally brings in cooler air.

The VEERING associates with WAA and BACKING associates with CAA dictum
is a synoptic scale mid-latitude rule of thumb. There is no 100%
guarantee that veering produces WAA and backing produces CAA,
especially when winds are light or the temperature gradient is
barotropic. In the warm sector of a mid-latitude cyclone the wind will
almost always veer with height (generally a WAA pattern will be
present). In the cold sector of a mid-latitude cyclone the wind will
almost always back with height (generally a CAA pattern will be
present). If you are in the tropics, in a light wind environment (such
as under a high), or in a barotropic environment the backing / veering
rule of thumb has very little relevance. The backing / veering rule of
thumb works well in the mid-latitudes near mid-latitude cyclones.
Thermal advection is most significant in the mid-latitudes and in the
vicinity of low pressure or a tight pressure gradient."

On Mon, 22 Apr 2013 11:25:52 +0100
"Bertie Doe" wrote:

Is there a rule of thumb for wind veering or backing with height?
Reason I ask: I often see actual wind say, bonfire smoke to differ by
60 degrees, with cloud-over-ground movement? TIA.


Rather depends on the height of the cloud as to what caused the
difference. Over land, the surface wind is generally backed by about
thirty degrees from the wind at about 2,000ft due to frictional forces.
See http://weatherfaqs.org.uk/node/75 for more complete info.

Wind velocity also changes with height depending on the temperature
distribution. This can be used to do your own forecasting when you see
clouds at two levels moving in different directions. If the wind is
backing with height, then cold air advection is occurring between the
two levels; conversely, if the wind is veering, warm advection is
occurring.

--
Graham P Davis, Bracknell, Berks.
Free office softwa http://www.libreoffice.org/
Carlos Seixas, Sonata nº 1 - best version of this I've found:
http://www.youtube.com/watch?v=YXox7vonfEg

On 22/04/2013 11:25, Bertie Doe wrote:
Is there a rule of thumb for wind veering or backing with height? Reason
I ask: I often see actual wind say, bonfire smoke to differ by 60
degrees, with cloud-over-ground movement? TIA.



In general wind veers and increases with height. Memories of fretting
over this on airfield layout for glider winching.

UKMO F214 spot wind forecast E.Anglia pm today gives 1000'
230/25knots, 2000' 240/30knots all the way up to 18000' 310/45knots.

Another useful source
http://rasp.inn.leedsmet.ac.uk/RASPt...SPtableGM.html where
you'll have to select 'soundings' from LH window, select the one you
want and see the wind speed and directions displayed on right of graph.

--
George in Epping, west Essex, 350'asl
www.eppingweather.co.uk
www.winter1947.co.uk

"George Booth" wrote in message
...
On 22/04/2013 11:25, Bertie Doe wrote:
Is there a rule of thumb for wind veering or backing with height? Reason
I ask: I often see actual wind say, bonfire smoke to differ by 60
degrees, with cloud-over-ground movement? TIA.



In general wind veers and increases with height. Memories of fretting over
this on airfield layout for glider winching.

UKMO F214 spot wind forecast E.Anglia pm today gives 1000' 230/25knots,
2000' 240/30knots all the way up to 18000' 310/45knots.

Another useful source
http://rasp.inn.leedsmet.ac.uk/RASPt...SPtableGM.html where you'll
have to select 'soundings' from LH window, select the one you want and see
the wind speed and directions displayed on right of graph.

--
George in Epping, west Essex, 350'asl
www.eppingweather.co.uk
www.winter1947.co.uk

Not quite the whole story George.

Your statement is only true in the boundary layer, below about 1km altitude.
This veering and increasing with height is caused by the frictional drag of
the surface. The degree of coupling between the surface air and that at 1 km
is an essential ingredient in maintaining the surface wind. If the coupling
is reduced, for example due to the establishment of a strong surface
temperature inversion (radiational night-time cooling), the surface wind
soon decreases to near calm, due to frictional drag. During the daytime,
coupling is at a maximum in an unstable boundary layer temperature profile,
and the surface wind speed and direction will be closest to that at 1 km
altitude.
As has been pointed out elsewhere, wind in the free atmosphere, that is,
above the surface boundary layer, veers with height in the presence of warm
advection, and backs in the presence of cold advection. The magnitude of the
vector change with height is directly related to the magnitude of the
thermal gradient. It is this type of effect you are seeing in the F214 winds
you quote.

--
Bernard Burton

Wokingham Berkshire.

Weather data and satellite images at:
http://www.woksat.info/wwp.html

Thanks all, that's much clearer. So rule of thumb is: winds Veer with height
in a warm air advection and Back in a cold air advection.

Just to quote yttiw's link from www.theweatherprediction "Winds often Veer
ahead of a cold front ... and Back behind a CF". So what would you expect to
happen, behind a warm front?

"Bernard Burton" wrote in message
...
"George Booth" wrote in message
...
On 22/04/2013 11:25, Bertie Doe wrote:
Is there a rule of thumb for wind veering or backing with height? Reason
I ask: I often see actual wind say, bonfire smoke to differ by 60
degrees, with cloud-over-ground movement? TIA.



In general wind veers and increases with height. Memories of fretting
over this on airfield layout for glider winching.

UKMO F214 spot wind forecast E.Anglia pm today gives 1000' 230/25knots,
2000' 240/30knots all the way up to 18000' 310/45knots.

Another useful source
http://rasp.inn.leedsmet.ac.uk/RASPt...SPtableGM.html where you'll
have to select 'soundings' from LH window, select the one you want and
see the wind speed and directions displayed on right of graph.

--
George in Epping, west Essex, 350'asl
www.eppingweather.co.uk
www.winter1947.co.uk

Not quite the whole story George.

Your statement is only true in the boundary layer, below about 1km
altitude. This veering and increasing with height is caused by the
frictional drag of the surface. The degree of coupling between the surface
air and that at 1 km is an essential ingredient in maintaining the surface
wind. If the coupling is reduced, for example due to the establishment of
a strong surface temperature inversion (radiational night-time cooling),
the surface wind soon decreases to near calm, due to frictional drag.
During the daytime, coupling is at a maximum in an unstable boundary layer
temperature profile, and the surface wind speed and direction will be
closest to that at 1 km altitude.
As has been pointed out elsewhere, wind in the free atmosphere, that is,
above the surface boundary layer, veers with height in the presence of
warm advection, and backs in the presence of cold advection. The magnitude
of the vector change with height is directly related to the magnitude of
the thermal gradient. It is this type of effect you are seeing in the F214
winds you quote.
And of course it is all specific to the hemisphere that you are observing
in. In the southern hemisphere, frictional retardation causes backing of
the flow with height in the lower boundary layer; and in the southern
hemisphere winds veering with height indicate cold advection, and winds
backing with height indicate warm advection.

I bet it's as clear as mud now! ;-)
--
Freddie
Bayston Hill
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/#!/BaystonHillWx for hourly reports

"Bernard Burton" wrote in message
...
"George Booth" wrote in message
...
On 22/04/2013 11:25, Bertie Doe wrote:
Is there a rule of thumb for wind veering or backing with height?
Reason
I ask: I often see actual wind say, bonfire smoke to differ by 60
degrees, with cloud-over-ground movement? TIA.



In general wind veers and increases with height. Memories of fretting
over this on airfield layout for glider winching.

UKMO F214 spot wind forecast E.Anglia pm today gives 1000' 230/25knots,
2000' 240/30knots all the way up to 18000' 310/45knots.

Another useful source
http://rasp.inn.leedsmet.ac.uk/RASPt...SPtableGM.html where
you'll have to select 'soundings' from LH window, select the one you
want and see the wind speed and directions displayed on right of graph.

--
George in Epping, west Essex, 350'asl
www.eppingweather.co.uk
www.winter1947.co.uk

As has been pointed out elsewhere, wind in the free atmosphere, that is,
above the surface boundary layer, veers with height in the presence of
warm advection, and backs in the presence of cold advection. The
magnitude of the vector change with height is directly related to the
magnitude of the thermal gradient. It is this type of effect you are
seeing in the F214 winds you quote.

And of course it is all specific to the hemisphere that you are observing
in. In the southern hemisphere, frictional retardation causes backing of
the flow with height in the lower boundary layer; and in the southern
hemisphere winds veering with height indicate cold advection, and winds
backing with height indicate warm advection.

I bet it's as clear as mud now! ;-)
--
Freddie
Bayston Hill
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/#!/BaystonHillWx for hourly reports

Yes, thanks Freddie. I didn't include that aspect for clarity, but you are
of course correct.

Behind a warm front, in the 'text book' case, there would be a region of no
thermal advection, = no change in wind direction with height. But truely
'tect book' cases are rare.

--
Bernard Burton

Wokingham Berkshire.

Weather data and satellite images at:
http://www.woksat.info/wwp.html

"Freddie" wrote in message
...

"Freddie" wrote in message ...
And of course it is all specific to the hemisphere that you are observing
in. In the southern hemisphere, frictional retardation causes backing of
the flow with height in the lower boundary layer; and in the southern
hemisphere winds veering with height indicate cold advection, and winds
backing with height indicate warm advection.

I bet it's as clear as mud now! ;-)

It's as clear as an unmuddied lake, Fred.

http://www.imdb.com/title/tt0066921/...item=qt0424854
;-)