On Dec 11, 5:52*pm, Dave Cornwell wrote:
how accurate (in %age terms) is the GFS at 120h ?

-----------------------------
Who knows for sure? 60% ??
Dave









The secret with GFS is not to take any particular frame literally, but
to monitor the time period you are interested in on a run by run
basis. The general trend on the previous three runs is for an intense
low to be somewhere over northern Scotland between 18Z Thursday and
06Z on Friday.

The 12Z run has the centre a little further south, but the low centre
continues to be forecast at below 950mb (and maybe 940 for a time).

Therefore I would say that the accuracy on a slightly larger spatial/
time scale is higher than 60%, maybe as high as 80 in this case.

On Dec 11, 5:34*pm, fred wrote:
On Dec 11, 3:31*pm, Richard Dixon wrote:





On Dec 11, 2:27*pm, "

wrote:
On Dec 11, 10:39*am, Adam Lea wrote:

On11/12/11 09:41, Weatherlawyer wrote:

On Dec 11, 12:16 am, Adam *wrote:
On10/12/11 23:39, graeme whipps wrote:

Wonder how many wind turbines will bite the dust this week, perhaps we
could measure the strength of a storm by the number of damaged
turbines.

If you look at the 120hr forecast from the ECMWF he

http://tinyurl.com/d94zjju

the 850mb wind speed has gone off the scale! Never seen that before.

It has, you are right. I can' see it.

I couldn't see any temperatures there, either.

So, meantime, how odd is a 90mph wind at that height?

90 mph sustained - not that common I wouldn't have thought, in the
vicinity of the UK anyway.

I would estimate that the 850mb sustained wind speed would approximate
the peak gust speed at ground level, so 90+ mph gusts near the surface.

The 0600 GFS T+120 has a low of 940mb just off Fraserburgh.

I do hope that it is wrong.

....and an 85 mph sustained wind over the sea.

how accurate (in %age terms) is the GFS at 120h ?- Hide quoted text -

- Show quoted text -

Model comparisons he

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz5.html

On Dec 11, 6:06*pm, "Eskimo Will" wrote:
"fred" wrote in message

...

how accurate (in %age terms) is the GFS at 120h ?

Never mind the GFS detail Fred, look at the synoptics. A circa 200 knot has
been consistently forecast to slam into England and Wales on Friday.
Associated with this will be a deepening depression of the order 940 hPa
with a wind field wider than last Thursday's storm due to a different
deepening mechanism (Norwegian left exit and high specific humidity
entrained as opposed to Shapiro Keyser - confluent trough/right entrance
runner). This means that the damaging storm force winds will be spread over
a wider area. Precise track depends critically on when the deepening phase
will begin. High risk area has to be northern England to central Scotland
for the most damaging winds, but the MetO will refine that in due course. If
I was you Fred I'd prepare for a storm of greater ferocity, and longer
lasting than last week and hope for the best. My personal feeling is that
northern England should be very worried too and all parts of the UK will at
least have gales, except perhaps the far north on the northern side of low,
but even here the northerly could be fierce. This is a serious low system
and should not be under-estimated.

http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

Bugger, I was kind of hoping it would track a wee bit further south -
but the deeper it gets the more to the north it will go. We got really
thumped last week as Hurricane Bawbag exited stage right. Power has
still not been 100% restored and Hydro Board engineers were out at a
line down our road at 11pm last night to make things safe. It will be
interesting to see how the English civil authorities deal with this -
Up here, we are used to mental weather and are geared up for it to a
certain extent in as much as our infrastructure is newer ( because it
has blown down more often and more recently and consequently been
replaced). We have had "get ready for winter" messages from dawn till
dusk on all media sources bar messenger pigeons for weeks now. Our
transport Minister's head rolled last year - so you can bet there was
a lesson learned there for a young administration. And we hold all the
road grit in Western Europe in a big garden shed between Edinburgh and
Glasgow

The eye of 940mb off Fraserburgh suits me fine from a personal self
interest/protectionist position

Odd are this one will be Christened Hurricane Fannybaws.

On Dec 11, 6:20*pm, Dawlish wrote:
On Dec 11, 5:34*pm, fred wrote:









On Dec 11, 3:31*pm, Richard Dixon wrote:

On Dec 11, 2:27*pm, "

wrote:
On Dec 11, 10:39*am, Adam Lea wrote:

On11/12/11 09:41, Weatherlawyer wrote:

On Dec 11, 12:16 am, Adam *wrote:
On10/12/11 23:39, graeme whipps wrote:

Wonder how many wind turbines will bite the dust this week, perhaps we
could measure the strength of a storm by the number of damaged
turbines.

If you look at the 120hr forecast from the ECMWF he

http://tinyurl.com/d94zjju

the 850mb wind speed has gone off the scale! Never seen that before.

It has, you are right. I can' see it.

I couldn't see any temperatures there, either.

So, meantime, how odd is a 90mph wind at that height?

90 mph sustained - not that common I wouldn't have thought, in the
vicinity of the UK anyway.

I would estimate that the 850mb sustained wind speed would approximate
the peak gust speed at ground level, so 90+ mph gusts near the surface.

The 0600 GFS T+120 has a low of 940mb just off Fraserburgh.

I do hope that it is wrong.

....and an 85 mph sustained wind over the sea.

how accurate (in %age terms) is the GFS at 120h ?- Hide quoted text -

- Show quoted text -

Model comparisons he

http://www.emc.ncep.noaa.gov/gmb/STATS/html/acz5.html

Goodness - Although I struggled through compulsory Medical Statistics
at Uni - I haven't a feckin clue what that says

On 11/12/2011 18:06, Eskimo Will wrote:

"fred" wrote in message
...
how accurate (in %age terms) is the GFS at 120h ?

Never mind the GFS detail Fred, look at the synoptics. A circa 200 knot
has been consistently forecast to slam into England and Wales on Friday.
Associated with this will be a deepening depression of the order 940 hPa
with a wind field wider than last Thursday's storm due to a different
deepening mechanism (Norwegian left exit and high specific humidity
entrained as opposed to Shapiro Keyser - confluent trough/right entrance
runner). This means that the damaging storm force winds will be spread
over a wider area. Precise track depends critically on when the
deepening phase will begin. High risk area has to be northern England to
central Scotland for the most damaging winds, but the MetO will refine
that in due course. If I was you Fred I'd prepare for a storm of greater
ferocity, and longer lasting than last week and hope for the best. My
personal feeling is that northern England should be very worried too and
all parts of the UK will at least have gales, except perhaps the far
north on the northern side of low, but even here the northerly could be
fierce. This is a serious low system and should not be under-estimated.

http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

With regards to the track of this system, I've seen elsewhere comments
such as as 'as the pressure drops, the low will veer North' or something
like that at least!

My question is why? Why will a deepening low pressure system move North
rather than South?

Sorry if it's a 'stoopid' question but despite having been lurking for a
few years, I'm still very much a Newb as far as the fluid dynamics of
the atmosphere is concerned!

BTW, Will - With comments like "200 knot . . . forecast to *slam* into
England and Wales on Friday", you might be able to get a part time job
at the Daily Excess when you retire - I'm sure 'slam' isn't a technical
term

Thanks

Neil

On Dec 11, 7:52*pm, Neil
wrote:
On 11/12/2011 18:06, Eskimo Will wrote:











"fred" wrote in message
...
how accurate (in %age terms) is the GFS at 120h ?

Never mind the GFS detail Fred, look at the synoptics. A circa 200 knot
has been consistently forecast to slam into England and Wales on Friday..
Associated with this will be a deepening depression of the order 940 hPa
with a wind field wider than last Thursday's storm due to a different
deepening mechanism (Norwegian left exit and high specific humidity
entrained as opposed to Shapiro Keyser - confluent trough/right entrance
runner). This means that the damaging storm force winds will be spread
over a wider area. Precise track depends critically on when the
deepening phase will begin. High risk area has to be northern England to
central Scotland for the most damaging winds, but the MetO will refine
that in due course. If I was you Fred I'd prepare for a storm of greater
ferocity, and longer lasting than last week and hope for the best. My
personal feeling is that northern England should be very worried too and
all parts of the UK will at least have gales, except perhaps the far
north on the northern side of low, but even here the northerly could be
fierce. This is a serious low system and should not be under-estimated.

http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

With regards to the track of this system, I've seen elsewhere comments
such as as 'as the pressure drops, the low will veer North' or something
like that at least!

My question is why? Why will a deepening low pressure system move North
rather than South?

Sorry if it's a 'stoopid' question but despite having been lurking for a
few years, I'm still very much a Newb as far as the fluid dynamics of
the atmosphere is concerned!

BTW, Will - With comments like "200 knot . . . forecast to *slam* into
England and Wales on Friday", you might be able to get a part time job
at the Daily Excess when you retire - I'm sure 'slam' isn't a technical
term

Thanks

Neil

I had assumed it was an inverse theta centrifugal mechanisim at play

"Neil" wrote in message
b.com...
On 11/12/2011 18:06, Eskimo Will wrote:

"fred" wrote in message
...
how accurate (in %age terms) is the GFS at 120h ?

Never mind the GFS detail Fred, look at the synoptics. A circa 200 knot
has been consistently forecast to slam into England and Wales on Friday.
Associated with this will be a deepening depression of the order 940 hPa
with a wind field wider than last Thursday's storm due to a different
deepening mechanism (Norwegian left exit and high specific humidity
entrained as opposed to Shapiro Keyser - confluent trough/right entrance
runner). This means that the damaging storm force winds will be spread
over a wider area. Precise track depends critically on when the
deepening phase will begin. High risk area has to be northern England to
central Scotland for the most damaging winds, but the MetO will refine
that in due course. If I was you Fred I'd prepare for a storm of greater
ferocity, and longer lasting than last week and hope for the best. My
personal feeling is that northern England should be very worried too and
all parts of the UK will at least have gales, except perhaps the far
north on the northern side of low, but even here the northerly could be
fierce. This is a serious low system and should not be under-estimated.

http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm
Will Hand (Haytor, Devon, 1017 feet asl)
---------------------------------------------

With regards to the track of this system, I've seen elsewhere comments
such as as 'as the pressure drops, the low will veer North' or something
like that at least!

My question is why? Why will a deepening low pressure system move North
rather than South?


Occasionally they do move south. What happens is that the low distorts the
thickness field through differential advection of warm and cold air.
Depressions are steered along the thickness (mean temperature) gradient.
Sometimes if the warm advection is stronger this distorts the thickness
pattern in such a way as to veer the thickness gradient and the low moves
SE, but mostly yes they do turn left. there are other dynamics going on such
as conservation of vorticity etc, but I'll leave that.

HTH

Will
--

wrote:
On Dec 11, 5:52 pm, Dave Cornwell wrote:
how accurate (in %age terms) is the GFS at 120h ?
-----------------------------
Who knows for sure? 60% ??
Dave









The secret with GFS is not to take any particular frame literally, but
to monitor the time period you are interested in on a run by run
basis. The general trend on the previous three runs is for an intense
low to be somewhere over northern Scotland between 18Z Thursday and
06Z on Friday.

The 12Z run has the centre a little further south, but the low centre
continues to be forecast at below 950mb (and maybe 940 for a time).

Therefore I would say that the accuracy on a slightly larger spatial/
time scale is higher than 60%, maybe as high as 80 in this case.

---------------------
I think the answer should have been accuracy of what, really? e.g,
position of low, wind speed, temperature. So many factors all with
different levels of accuracy.
Dave

On Dec 11, 8:43*pm, Dave Cornwell wrote:
wrote:
On Dec 11, 5:52 pm, Dave Cornwell wrote:
how accurate (in %age terms) is the GFS at 120h ?
-----------------------------
Who knows for sure? 60% ??
Dave

The secret with GFS is not to take any particular frame literally, but
to monitor the time period you are interested in on a run by run
basis. The general trend on the previous three runs is for an intense
low to be somewhere over northern Scotland between 18Z Thursday and
06Z on Friday.

The 12Z run has the centre a little further south, but the low centre
continues to be forecast at below 950mb (and maybe 940 for a time).

Therefore I would say that the accuracy on a slightly larger spatial/
time scale is higher than 60%, maybe as high as 80 in this case.

---------------------
I think the answer should have been accuracy of what, really? e.g,
position of low, wind speed, temperature. So many factors all with
different levels of accuracy.
Dave- Hide quoted text -

- Show quoted text -

That's true. The stats from NCEP are determined by the accuracy of the
500hpa contour chart, I believe.

Fred; as far as that goes, model accuracy could be judged as pretty
good at 5 days. gfs has performed well recently, but ECM is almost
always ahead, averaged over a month.

Dave's right though. What really counts is the weather one experiences
on the ground. Now the accuracy there is a whole different kettle of
fish!

On Sun, 11 Dec 2011 10:07:05 -0800 (PST), wrote:

The general trend on the previous three runs is for an intense
low to be somewhere over northern Scotland between 18Z Thursday and
06Z on Friday.

So there might be a biggie on Thursday night, this follows what looks
like still quite a nasty on Tuesday afternoon/evening...

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.