Veering or Backing with height

[Bertie Doe]

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.

[Buchan Meteo]

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

[yttiw]

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."

[Graham P Davis]

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 software: http://www.libreoffice.org/
Carlos Seixas, Sonata nº 1 - best version of this I've found:
http://www.youtube.com/watch?v=YXox7vonfEg

[George Booth]

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/RASPtableGM9/RASPtableGM.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

[Bernard Burton]

"George Booth" <george....@ntlworld.com> wrote in message
news:atkntd...@mid.individual.net...

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

[Bertie Doe]

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?

[Freddie]

"Bernard Burton" <b.j.b...@btinternet.com> wrote in message
news:atkvd6...@mid.individual.net...

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]

>
> "Bernard Burton" <b.j.b...@btinternet.com> wrote in message
> news:atkvd6...@mid.individual.net...
>> "George Booth" <george....@ntlworld.com> wrote in message
>> news:atkntd...@mid.individual.net...
>>> 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/RASPtableGM9/RASPtableGM.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" <ni...@hosiene.co.uk> wrote in message
news:kl3jv9$9ko$1...@news.albasani.net...

[Bertie Doe]

"Freddie" wrote in message news:kl3jv9$9ko$1...@news.albasani.net...

>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/quotes?item=qt0424854
;-)

[Freddie]

>>I bet it's as clear as mud now! ;-)
>
> It's as clear as an unmuddied lake, Fred.
>

Ah, but can I rely on you? ;-)

[Bernard Burton]

"Bertie Doe" <monteb...@ntl.com> wrote in message
news:atl26k...@mid.individual.net...

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, in the "warm
sector". But truely 'text book' cases are rare.

>"Winds often Veer ahead of a cold front ... and Back behind a CF".

Winds often veer with height ahead of a WARM front. As warm fronts
traditionally preceed cold fronts, the statement above could be true in a
non-false sense, but does not convey the whole picture.

[Bertie Doe]

"Bernard Burton" wrote in message news:atl38u...@mid.individual.net...

>
>Winds often veer with height ahead of a WARM front. As warm fronts
>traditionally preceed cold fronts, the statement above could be true in a
>non-false sense, but does not convey the whole picture.

Thanks Bernard, I was experiencing a senior moment and got my fronts
back-to-front.

[George Booth]

On 22/04/2013 15:22, Bernard Burton wrote:
> "George Booth" <george....@ntlworld.com> wrote in message
> news:atkntd...@mid.individual.net...
>> 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/RASPtableGM9/RASPtableGM.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.

Thanks Bernard at al for the full explanation. Unfortunately my highest
winch launch was 2200' well within the boundary layer. Others have done
better though.

[Lindisfarne Poacher]

On Mon, 22 Apr 2013 17:52:54 +0100, George Booth wrote:

<snip>

> Thanks Bernard at al for the full explanation. Unfortunately my highest
> winch launch was 2200' well within the boundary layer. Others have done
> better though.

I seem to recall that a lot of research on boundary layer stuff was done
at RAF Cardington near Bedford using "BALTHUM" equipment.

http://www.sciencephoto.com/media/158202/view

I think a lot of "secret squirrel" stuff also went on there judging by
the reaction of a certain forecaster I worked with when that station was
mentioned in conversation!

[George Booth]

Such as this one. http://www.youtube.com/watch?v=-VlRd9-wxQI over
4500'off the winch at 1.38 on the video.

[Sytze Stel]

"Lindisfarne Poacher" <lindisfar...@spam-me-notgmail.com> schreef in
bericht news:kl3r04$bce$1...@dont-email.me...

[Sytze Stel]

Van: "Lindisfarne Poacher" <lindisfar...@spam-me-notgmail.com>
Onderwerp: Re: Veering or Backing with height
Datum: maandag 22 april 2013 19:11

On Mon, 22 Apr 2013 17:52:54 +0100, George Booth wrote:

<snip>

> Thanks Bernard at al for the full explanation. Unfortunately my highest
> winch launch was 2200' well within the boundary layer. Others have done
> better though.

>I seem to recall that a lot of research on boundary layer stuff was done
>at RAF Cardington near Bedford using "BALTHUM" equipment.

>http://www.sciencephoto.com/media/158202/view

>I think a lot of "secret squirrel" stuff also went on there judging by
>the reaction of a certain forecaster I worked with when that station was
>mentioned in conversation!

For an couple of weeks a collegue and I, both Dutch AC2's, did the weather
observations during the time a barrage balloon equiped with a thermometer, a
hygrometer and a Robinson windspeed meter went up - an down.
Mr. Ferguson let the balloon rise while mr. McCan, in a hut, read the data
from a screen.
As far as I remember the maximum height must have been around 4000 ft.
Another thing I remember are tiny fluctuations in temperature while looking
at the mercury in the Stevenson screen. Was it possible to measure the wind
direction with height? I don't know.
'Secret squirrel stuff' was not noticed in 1945. Later perhaps, and what
could it be?
All this in september 1945 in Cardington while we were waiting to go to the
Air Ministry Meteorological Training School in Kilburn, London NW.

Sytze Stel, Netherlands

[Lindisfarne Poacher]

Sytze Stel <rint...@xs4all.nl> wrote:

> For an couple of weeks a collegue and I, both Dutch AC2's, did the weather
> observations during the time a barrage balloon equiped with a thermometer, a
> hygrometer and a Robinson windspeed meter went up - an down.
> Mr. Ferguson let the balloon rise while mr. McCan, in a hut, read the data
> from a screen.
> As far as I remember the maximum height must have been around 4000 ft.
> Another thing I remember are tiny fluctuations in temperature while looking
> at the mercury in the Stevenson screen. Was it possible to measure the wind
> direction with height? I don't know.
> 'Secret squirrel stuff' was not noticed in 1945. Later perhaps, and what
> could it be?
> All this in september 1945 in Cardington while we were waiting to go to the
> Air Ministry Meteorological Training School in Kilburn, London NW.

Gosh! That was a long time ago. I was referring to the 1970's when the
Cold War was still going on. Perhaps the guy was involved in some armed
forces exercise involving Cardington? My only tiny experience with
temperature sounding was with a Graw Sonde at the Met Office Training
School at Shinfield near Reading, again in the 70's.