Was expecting today to be quite a good day in the south (south
Hampshire specifically), particularly given the cold front was weak
down here and it was fine late yesterday. Was hoping to get out today
given the prospects of "Bill" tomorrow but seems to be turning into a
disturbed day with heavy showers about, possibly the most disturbed
day in the south since the 6th. Temperatures really struggling as
well, e.g. 17C at Heathrow or 16C at Cardiff at 1100BST which seems a
couple of degrees below the norm for that time of day.

Looking at the Met Office suggestion of "Bill" not doing much in the
southeast maybe today will be the worst day of the week round here!

Nick

"Nick" wrote ...
Was expecting today to be quite a good day in the south (south
Hampshire specifically), particularly given the cold front was weak
down here and it was fine late yesterday. Was hoping to get out
today
given the prospects of "Bill" tomorrow but seems to be turning into
a
disturbed day with heavy showers about, possibly the most disturbed
day in the south since the 6th. Temperatures really struggling as
well, e.g. 17C at Heathrow or 16C at Cardiff at 1100BST which seems
a
couple of degrees below the norm for that time of day.

.... one of those situations when the surface charts doesn't really do
justice to the situation; there is a marked upper trough (colder air
throughout troposphere in this case, relative to either side) swinging
from west to east, being hustled along by events further west and
relaxing (i.e. lessening the dynamic / vorticity forcing), but still
enough of a force hereabouts to give short-lived moderate, locally
heavy showers - they're not lasting long (15 mins at most).

http://www.wzkarten.de/pics/Rtavn001.png

should improve as the trough moves on and we get descent to its rear.
On the GFS timing, the axis of the trough should be passing overhead
here ~midday GMT.

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

"Martin Rowley" wrote in message ...

... one of those situations when the surface charts doesn't really
do justice to the situation; there is a marked upper trough (colder
air throughout troposphere in this case, relative to either side)
swinging from west to east, being hustled along by events further
west and relaxing (i.e. lessening the dynamic / vorticity forcing),
but still enough of a force hereabouts to give short-lived moderate,
locally heavy showers - they're not lasting long (15 mins at most).

http://www.wzkarten.de/pics/Rtavn001.png

should improve as the trough moves on and we get descent to its
rear. On the GFS timing, the axis of the trough should be passing
overhead here ~midday GMT.


.... and just about on time, we duly had a complete change in
'skyscape' with Cu now much shallower - not capped as the air is still
unstable, but I suspect that the mid-level moisture has changed and
won't sustain the taller convective towers, at least hereabouts -
obviously still perky over the spine of Devon & Cornwall & over Wales.
Also, scrappy elements of layer Ac which indicates some medium-level
descent/stabilisation going on.

However, the trough can't be as straightforward as that image posted
(ex GFS) as looking carefully at the cloud elements I can see that the
cloud winds aren't following the simple shape indicated. Going back to
the 00Z plots of actual upper winds at 700 and 500hPa, it's clear that
the trough was being distorted by the developments further out in the
Atlantic (ex-Bill), and Valentia winds in particular didn't verify too
well against background: a common problem with such developments. Even
the model 700hPa trough isn't anything like as symmetrical as the 500
hPa for example.

.... in major forecasting centres (such as Exeter), they will overlay
water vapour imagery in particular against other imagery and model
fields - modern NWP suites can produce 'pseudo WV' fields - and such
errors are quickly picked out and can be allowed for.

However we seem to be poorly off for real-time WV imagery - I can't
find a loop of such - does anyone know of a source?

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

"Martin Rowley" wrote in message
...

... in major forecasting centres (such as Exeter), they will overlay water
vapour imagery in particular against other imagery and model fields -
modern NWP suites can produce 'pseudo WV' fields - and such errors are
quickly picked out and can be allowed for.

However we seem to be poorly off for real-time WV imagery - I can't find a
loop of such - does anyone know of a source?

Martin.

http://oiswww.eumetsat.org/IPPS/html...2/BW/index.htm
click on the region of interest to access the loop

I'll endeavour to provide a pseudo water vapour example that Martin
mentions.

Jon.

On Aug 25, 1:41*pm, "Jon O'Rourke" wrote:
"Martin Rowley" wrote in message

...

... in major forecasting centres (such as Exeter), they will overlay water
vapour imagery in particular against other imagery and model fields -
modern NWP suites can produce 'pseudo WV' fields - and such errors are
quickly picked out and can be allowed for.

However we seem to be poorly off for real-time WV imagery - I can't find a
loop of such - does anyone know of a source?

Martin.

http://oiswww.eumetsat.org/IPPS/html...2/BW/index.htm
click on the region of interest to access the loop

I'll endeavour to provide a pseudo water vapour example that Martin
mentions.

Jon.

Thanks for that link Jon. That is excellent.

One question that puzzles me, and concerns the contrast on the IR
frames. North Africa looks very dark (due to the high temperatures
there), but the cloud contrast does not seem to show the thick cloud
associated with ex-Bill as particularly white. Could this be my
laptop, or are the cloud tops relatively warm? Or is it just that the
really bright white shade is reserved for the added coastlines?

Stuart

"Jon O'Rourke" wrote in message
...

http://oiswww.eumetsat.org/IPPS/html...2/BW/index.htm
click on the region of interest to access the loop

I'll endeavour to provide a pseudo water vapour example that Martin
mentions.


.... thanks for that Jon: a 'red face' moment coming up, as I had found
that site (one of the first I looked at), but couldn't get it to do
anything: now I've just realised - you have to click on the *name* of
the area to get it to respond!

Martin.


--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N Long: 01.88W
NGR: SU 082 023

On 25 Aug, 13:26, "Martin Rowley"
wrote:
"Martin Rowley" *wrote in message ...

... one of those situations when the surface charts doesn't really
do justice to the situation; there is a marked upper trough (colder
air throughout troposphere in this case, relative to either side)
swinging from west to east, being hustled along by events further
west and relaxing (i.e. lessening the dynamic / vorticity forcing),
but still enough of a force hereabouts to give short-lived moderate,
locally heavy showers - they're not lasting long (15 mins at most).

http://www.wzkarten.de/pics/Rtavn001.png

should improve as the trough moves on and we get descent to its
rear. On the GFS timing, the axis of the trough should be passing
overhead here ~midday GMT.

... and just about on time, we duly had a complete change in
'skyscape' with Cu now much shallower - not capped as the air is still
unstable, but I suspect that the mid-level moisture has changed and
won't sustain the taller convective towers, at least hereabouts -
obviously still perky over the spine of Devon & Cornwall & over Wales.
Also, scrappy elements of layer Ac which indicates some medium-level
descent/stabilisation going on.

However, the trough can't be as straightforward as that image posted
(ex GFS) as looking carefully at the cloud elements I can see that the
cloud winds aren't following the simple shape indicated. Going back to
the 00Z plots of actual upper winds at 700 and 500hPa, it's clear that
the trough was being distorted by the developments further out in the
Atlantic (ex-Bill), and Valentia winds in particular didn't verify too
well against background: a common problem with such developments. Even
the model 700hPa trough isn't anything like as symmetrical as the 500
hPa for example.

... in major forecasting centres (such as Exeter), they will overlay
water vapour imagery in particular against other imagery and model
fields - modern NWP suites can produce 'pseudo WV' fields - and such
errors are quickly picked out and can be allowed for.

However we seem to be poorly off for real-time WV imagery - I can't
find a loop of such - does anyone know of a source?

Martin.

--
Martin Rowley
West Moors, East Dorset (UK): 17m (56ft) amsl
Lat: 50.82N * Long: 01.88W
NGR: SU 082 023

Down here the trough seemed to clear eastwards around 08:00, but then
another line of stratocumulus/embedded cumulus around 10:30, with a
few spots of rain. Since then good sunny periods, with the cumulus
mainly in it's normal 'spinal' location

After the coolest night since 9th (Min 11.5C) the temperature was
initially very slow to rise, but has risen steadily since 11:00 to
reach 19.7C currently, making it the warmest day here since 20th
(yesterday 19.1 max). Noticeably cooler inland under the cloudy strip.

19C and still fine out on Scilly. www.scillyman.co.uk/Web_Cam.html /
www.scillyman.co.uk/Web_Cam.html In fact it sill looks pretty calm out
there.

On a slightly different topic, maximum temperatures on Scilly &
coastal west Cornwall, seem to have been relatively high this year
compared with inland parts of Devon/Cornwall. I can't see that this is
due to the SST anomalies, so I can only put it down to the
differential between the sunshine on the coast, and that inland, being
greater than normal this summer. (It may be I'm being influenced by
the cold conditions in the far SW last year, when average maximum
temperatures in August were easily the lowest I've recorded - since
1991).

If anyone has access to maximum temperature data for St Mary's (I've
got Penzance!) and for a scattering of other locations in Cornwall/
Devon, for July/Aug for say the last 3 or 4 years, it would allow me
to compare the differentials. I hope to get data for St Martins.

Well, as there's still no sign of the cloud steaming ahead of 'Bill',
and the breeze is only of Force 3 or so, I'm off to Lamorna to do a
bit of snorkelling before it all gets stirred up.

Graham
Penzance

www.turnstone-cottage.co.uk/recent.html

"sutartsorric" wrote in message
...

One question that puzzles me, and concerns the contrast on the IR
frames. North Africa looks very dark (due to the high temperatures
there), but the cloud contrast does not seem to show the thick cloud
associated with ex-Bill as particularly white. Could this be my
laptop, or are the cloud tops relatively warm? Or is it just that the
really bright white shade is reserved for the added coastlines?

I would hazard a guess it's largely down to the way the image is being
processed. Other sources, e.g.
http://wind.met.fu-berlin.de/cgi-bin...laymode=Endlos
perhaps offer better contrast and show some fairly vigorous ascent on the
forward side of the system.

VT 18Z WAFC data puts the tops at 26000FT
http://www.lfv.se/Tor/wc18/swc_18.asp
about 10000FT less than the CB over the continent in terms of a comparison.

Jon.

On Aug 25, 2:43*pm, "Jon O'Rourke" wrote:
"sutartsorric" wrote in message

...

One question that puzzles me, and concerns the contrast on the IR
frames. North Africa looks very dark (due to the high temperatures
there), but the cloud contrast does not seem to show the thick cloud
associated with ex-Bill as particularly white. Could this be my
laptop, or are the cloud tops relatively warm? Or is it just that the
really bright white shade is reserved for the added coastlines?

I would hazard a guess it's largely down to the way the image is being
processed. Other sources, e.g.http://wind.met.fu-berlin.de/cgi-bin...=12&count=16&i...
perhaps offer better contrast and show some fairly vigorous ascent on the
forward side of the system.

VT 18Z WAFC data puts the tops at 26000FThttp://www.lfv.se/Tor/wc18/swc_18.asp
about 10000FT less than the CB over the continent in terms of a comparison.

in 57197 20090825 115604 Nick wrote:
Was expecting today to be quite a good day in the south (south
Hampshire specifically), particularly given the cold front was weak
down here and it was fine late yesterday. Was hoping to get out today
given the prospects of "Bill" tomorrow but seems to be turning into a
disturbed day with heavy showers about, possibly the most disturbed
day in the south since the 6th. Temperatures really struggling as
well, e.g. 17C at Heathrow or 16C at Cardiff at 1100BST which seems a
couple of degrees below the norm for that time of day.

Looking at the Met Office suggestion of "Bill" not doing much in the
southeast maybe today will be the worst day of the week round here!

Nick

It was fine all day, though very windy, at Hayling Island after an early heavy shower.