Foehn Aberdeen - Pilots' weather
 

It was always fun landing at Aberdeen in these conditions:

EGPD 130950Z 28026G40KT 9999 FEW030 11/00 Q0990 NOSIG=

Splendidly turbulent wind some 60° off the runway. Real pilots'
weather.
(I don't suppose these cheapskate airlines even give out sick bags
nowadays. A quick spray of the cabin floor afterwards is apparently
considered adequate).

Note that low dewpoint of 0°C, a typical feature of foehn conditions.

Jack

Foehn Aberdeen - Pilots' weather
 

wrote:
It was always fun landing at Aberdeen in these conditions:

EGPD 130950Z 28026G40KT 9999 FEW030 11/00 Q0990 NOSIG=

Splendidly turbulent wind some 60° off the runway. Real pilots'
weather.
(I don't suppose these cheapskate airlines even give out sick bags
nowadays. A quick spray of the cabin floor afterwards is apparently
considered adequate).

Note that low dewpoint of 0°C, a typical feature of foehn conditions.

Jack


There is a nice item about the Föhn effect he

http://www.bbc.co.uk/weather/features/fohn_effect.shtml

Not especially warm here today (11) although generally in keeping with
recent days.

For those with english keyboards, Alt-0246 gives ö

--
Gianna

Foehn Aberdeen - Pilots' weather
 

Gianna wrote:


There is a nice item about the Föhn effect he

http://www.bbc.co.uk/weather/features/fohn_effect.shtml


--
Gianna

The explanation of the föhn is not really adequate. The air
in the lee of the mountains has mostly *not* risen, condensed out its
moisture and descended again, but comes from a higher level to the
windward of the mountains and descends in the lee. The simple
explanation given cannot explain the high temperatures and low
humidities experienced, at least in most cases. No-one is going to
convince me that an airstream climbs up the Alps and then drops down
again. Air doesn't like going uphill unless very unstable, in which
case it wouldn't descend the other side.

Tudor Hughes, Warlingham, Surrey

Foehn Aberdeen - Pilots' weather
 

My degree symbol is made by Alt +248

Alt 0246 does indeed give ö so Föhn if you prefer.

But Alt+246 (no leading zero) gives ÷

This is all horribly off-topic, but isn't it fun?

For all the codes (I love the url - "stuff")
http://www.theworldofstuff.com/characters/

Jack

[O/T] Alt codes - was Föhn Aberdeen - Pilots' weather
 

wrote:
My degree symbol is made by Alt +248

or by Alt+0176

Alt 0246 does indeed give ö so Föhn if you prefer.

I do tend to, because we can.

But Alt+246 (no leading zero) gives ÷

Mmm it does.

This is all horribly off-topic, but isn't it fun?

Yes, it is (to both) (-:

For all the codes (I love the url - "stuff")
http://www.theworldofstuff.com/characters/

Ah, I just use the character map (Start|Programs|Accessories|System
Tools|Character Map).

--
Gianna

Foehn Aberdeen - Pilots' weather
 

I would agree with most of your comments concerning descending air from
orographic effects. However, for convection, and especially deep convection,
much of air that ascends within the cloud descends over a much larger
volume, and mostly sinks rather slowly, if at all. Much of the cloud
material that was once the active cloud spreads out quasi-horizontally near
the cloud top, while a good deal is also mixed into the close environment of
where the cloud had been. Unless it is dynamically driven, it will tend to
soon spread out rather than descend very far, as it will mostly find itself
warmer than its environment due to adibatic heating, inhibiting descent.
Descent in and around deep convection is generated mainly by evaporative
cooling, as precipitation falls into dry air beneath, or where drier air is
entrained into the precipitation from the cloud's surroundings. This cooled
air leads to acceleration downwards, and can produce very strong surface
gusts when it is constrained to flow horizontally at the surface. It is
also the reason for the well documented 'downburst' phenomenon, that has led
to several aircraft accidents. It should also be noted that precipitation
itself drags air down as it falls, contributing to any acceleration due to
evaporation.
On occasions, air accelerated downwards by evaporative cooling can continue
to descend for a while after all the precipitation has evaporated, and
increasing temperature at the dry lapse rate may lead to it becoming warmer
than its environment. Then its arrival at the surface can lead to a rise in
temperature there, as the deceleration of the descending air takes time, the
restoring force not being very strong.




A very similar effect can occur near showers and storms. The air
spilling out near the tops of clouds heats at the dry adiabatic as it
descends. It kills the thermals (big clear holes on satpics) and can
on occasions manifest itself as a sudden rapid rise in surface
temperature. I have seen documented examples (Jersey rings a bell)
when the surface temperature rose several degrees in a matter of
minutes.

Jack












--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
wrote in message
oups.com...

Foehn Aberdeen - Pilots' weather
 

It is doubtless true that in general there is little descent round the
edges of active growing large cumulus. The received wisdom is for
pilots to steer well clear of such clouds. I found over years of
experience that you could fly with the wingtip almost brushing the
cloud and not feel a burble of turbulence. You do of course keep much
further away from active cunims but the risk here is not so much
turbulences as lightning strikes.

I expect to be taken to task for flying so close to large cumulus, but
I can't have been so wrong. 40 years as a professional (survivor)

Jack

Foehn Aberdeen - Pilots' weather
 

Bernard Burton wrote:

On occasions, air accelerated downwards by evaporative cooling can continue
to descend for a while after all the precipitation has evaporated, and
increasing temperature at the dry lapse rate may lead to it becoming warmer
than its environment. Then its arrival at the surface can lead to a rise in
temperature there, as the deceleration of the descending air takes time, the
restoring force not being very strong.

Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
wrote in message
oups.com...

This "downdraught overshoot" is quite rare, at least as far
as I know, but there was a notable case in Guernsey on 30 Jul 1983 (I
think). It must require a very high cloudbase.

Tudor Hughes, Warlingham, Surrey.

[O/T] Alt codes - was Föhn Aberdeen - Pilots' weather
 

Gianna wrote:

I just use the character map (Start|Programs|Accessories|System
Tools|Character Map).

But then of course you have a Windows machine with Office. (As you have
every right to.)

There are other operating systems (and offices) out there. Mind you
getting into OOo's character map is a pain if you just want to be exact
on a newsgroup.
(OOo Writer Insert Special Character)

Foehn Aberdeen - Pilots' weather
 

Tudor Hughes wrote:

The explanation of the föhn is not really adequate.

The use of the term "record" isn't much better.