I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!

On Sep 19, 9:36*pm, Dawlish wrote:
I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!

Ah, but those extra-tropical storms running up the east coast of
America are basically the cause of the more settled conditions will be
experiencing in the coming week or two.

Keith (Southend)

On Sun, 19 Sep 2010 at 13:36:21, Dawlish wrote in
uk.sci.weather :

I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

Preferably something nice & zonal for the week after, though...
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)

"Dawlish" wrote in message
...
I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!

The GFS at least has been flip-flopping like mad between low & high
pressure dominated weather for the past week or so.
--
Col

Bolton, Lancashire
160m asl

"Dawlish" wrote in message
...
I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!


Are you still sure about this Paul? I'm still going for a warm and wet
Autumn BTW.
You made this prediction at the worst possible time, before extratropical
transistion of Igor where models were indicating all sorts of subtle
dynamical possibilities despite the agreement you happened to find around
this time from succesive runs. Ex Igor warm air advection west of Greenland
will undoubtedly throw up an anticyclone downstream near UK, but as always
with these systems there is a high probability of them injecting energy into
the jet which will make the high topple and/or receed east. the latter now
looks like taking place. An interesting development is that ex Igor rotates
west of Greenland and injects cold air south towards Newfoundland by
strengthening northerly flow this also accentuating the jet. I would not be
at all surprised to see a stormy end to September (at least up north).

Will
--

On Sep 21, 6:59*pm, "Will Hand" wrote:
"Dawlish" wrote in message

...

I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!

Are you still sure about this Paul? I'm still going for a warm and wet
Autumn BTW.
You made this prediction at the worst possible time, before extratropical
transistion of Igor where models were indicating all sorts of subtle
dynamical possibilities despite the agreement you happened to find around
this time from succesive runs. Ex Igor warm air advection west of Greenland
will undoubtedly throw up an anticyclone downstream near UK, but as always
with these systems there is a high probability of them injecting energy into
the jet which will make the high topple and/or receed east. the latter now
looks like taking place. An interesting development is that ex Igor rotates
west of Greenland and injects cold air south towards Newfoundland by
strengthening northerly flow this also accentuating the jet. I would not be
at all surprised to see a stormy end to September (at least up north).

Will
--

I'm right 80% of the time Will, over 90 different forecasts at all
times of the year. That means I will be wrong once in 5 times. I
wouldn't be surprised to see a wet end to September in the far NW
either. 2 days ago, that's what I suggested may well happen. I don't
see this as the worst possible time to forecast; that implies that
other times are easier. 5 years of doing this have shown me there are
no "easy" times and the difficult times are when we see no agreement
and no consistency. An 80% success rate shows me the system works.

Judge the forecast at outcome and not 2 days in, is what I would
always say. As it stands now, I'm less confident than I was 2 days ago
and if this forecast is one of the 20% that end up as incorrect and it
ends up a wet end to Autumn - oh well! Let's wait another 8 days
though.

To link any changes directly to a particular extra-tropical storm,
however, I feel is wrong, as evidenced by no forecastability from the
past and several tropical storms already this autumn, most of which
have appeared to have very little attributable effect and at least one
of which you said would influence our weather, but didn't seemingly
inject any energy into the jet and we ended up with quiet and settled
conditions instead.

"Dawlish" wrote in message
...
On Sep 21, 6:59 pm, "Will Hand" wrote:
"Dawlish" wrote in message

...

I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!

Are you still sure about this Paul? I'm still going for a warm and wet
Autumn BTW.
You made this prediction at the worst possible time, before extratropical
transistion of Igor where models were indicating all sorts of subtle
dynamical possibilities despite the agreement you happened to find around
this time from succesive runs. Ex Igor warm air advection west of
Greenland
will undoubtedly throw up an anticyclone downstream near UK, but as always
with these systems there is a high probability of them injecting energy
into
the jet which will make the high topple and/or receed east. the latter now
looks like taking place. An interesting development is that ex Igor
rotates
west of Greenland and injects cold air south towards Newfoundland by
strengthening northerly flow this also accentuating the jet. I would not
be
at all surprised to see a stormy end to September (at least up north).

Will
--

I'm right 80% of the time Will, over 90 different forecasts at all
times of the year. That means I will be wrong once in 5 times. I
wouldn't be surprised to see a wet end to September in the far NW
either. 2 days ago, that's what I suggested may well happen. I don't
see this as the worst possible time to forecast; that implies that
other times are easier. 5 years of doing this have shown me there are
no "easy" times and the difficult times are when we see no agreement
and no consistency. An 80% success rate shows me the system works.

Judge the forecast at outcome and not 2 days in, is what I would
always say. As it stands now, I'm less confident than I was 2 days ago
and if this forecast is one of the 20% that end up as incorrect and it
ends up a wet end to Autumn - oh well! Let's wait another 8 days
though.

To link any changes directly to a particular extra-tropical storm,
however, I feel is wrong, as evidenced by no forecastability from the
past and several tropical storms already this autumn, most of which
have appeared to have very little attributable effect and at least one
of which you said would influence our weather, but didn't seemingly
inject any energy into the jet and we ended up with quiet and settled
conditions instead.
====================

You misunderstand Paul. All large extra-tropical storms will influence the
jet. Some will cause the jet to buckle (meridional extension) and may result
in a developing anticyclone and others will inject moisture and energy in
such a way as to make depressions more active or even help develop
downstream lows 1000 miles away like the low developing at the end of this
week, that has clear dynamical links to Igor. Technical briefings at work
have mentioned such effects for several weeks now and they are soundly based
in theory, like that paper I told you about. The fact that "outcomes" as you
put it do not appear to back up the theory is that models are not yet good
enough to model the fine interactions and dynamical processes during
extra-tropical transistion. A low going just west or just east of Greenland
is critical.

Will
--

On Sep 21, 8:09*pm, "Will Hand" wrote:
"Dawlish" wrote in message

...
On Sep 21, 6:59 pm, "Will Hand" wrote:





"Dawlish" wrote in message

...

I don't see a wet September. I have 75% confidence that high pressure
will be dominating our weather towards the end of the month.

**at T240, on Wednesday 29th September, most of the UK will be under
anticyclonic conditions, leading to quiet, dry and settled weather for
most**

A nice end to September. Dry days, some frost at night further north
and not a great deal of rain for most between now and then. No storms,
the jet to our NW, subsiding air over the UK and little evidence of
the influence of these extra-tropical depressions. The exception may
well be the far NW. That's my take on the weather at 10 days!

Are you still sure about this Paul? I'm still going for a warm and wet
Autumn BTW.
You made this prediction at the worst possible time, before extratropical
transistion of Igor where models were indicating all sorts of subtle
dynamical possibilities despite the agreement you happened to find around
this time from succesive runs. Ex Igor warm air advection west of
Greenland
will undoubtedly throw up an anticyclone downstream near UK, but as always
with these systems there is a high probability of them injecting energy
into
the jet which will make the high topple and/or receed east. the latter now
looks like taking place. An interesting development is that ex Igor
rotates
west of Greenland and injects cold air south towards Newfoundland by
strengthening northerly flow this also accentuating the jet. I would not
be
at all surprised to see a stormy end to September (at least up north).

Will
--

I'm right 80% of the time Will, over 90 different forecasts at all
times of the year. That means I will be wrong once in 5 times. I
wouldn't be surprised to see a wet end to September in the far NW
either. 2 days ago, that's what I suggested may well happen. I don't
see this as the worst possible time to forecast; that implies that
other times are easier. 5 years of doing this have shown me there are
no "easy" times and the difficult times are when we see no agreement
and no consistency. An 80% success rate shows me the system works.

Judge the forecast at outcome and not 2 days in, is what I would
always say. As it stands now, I'm less confident than I was 2 days ago
and if this forecast is one of the 20% that end up as incorrect and it
ends up a wet end to Autumn - oh well! Let's wait another 8 days
though.

To link any changes directly to a particular extra-tropical storm,
however, I feel is wrong, as evidenced by no forecastability from the
past and several tropical storms already this autumn, most of which
have appeared to have very little attributable effect and at least one
of which you said would influence our weather, but didn't seemingly
inject any energy into the jet and we ended up with quiet and settled
conditions instead.
====================

You misunderstand Paul. All large extra-tropical storms will influence the
jet. Some will cause the jet to buckle (meridional extension) and may result
in a developing anticyclone and others will inject moisture and energy in
such a way as to make depressions more active or even help develop
downstream lows 1000 miles away like the low developing at the end of this
week, that has clear dynamical links to Igor. Technical briefings at work
have mentioned such effects for several weeks now and they are soundly based
in theory, like that paper I told you about. The fact that "outcomes" as you
put it do not appear to back up the theory is that models are not yet good
enough to model the fine interactions and dynamical processes during
extra-tropical transistion. A low going just west or just east of Greenland
is critical.

Will
--- Hide quoted text -

- Show quoted text -

I don't misunderstand Will. I understand the theory. What I question
is the practical use of that theory in forecasting for the UK. I know
that small errors can produce large changes in outcome and I'm more
than aware of the fact that the models appear not to be capable, yet,
of modelling that well. If they were, this forecasting business
wouldn't be anything like as interesting, as forecasts would be mainly
correct at 10 days and we'd have little to argue the toss about!
However, the outcomes show that forecasts at that distance are pretty
hopeless - unless you are piers Corbyn, of course, in which case it's
easy!

That doesn't change what I've found about those outcomes by actually
forecasting. Whether I forecast when extra-tropical cyclones are on
the horizon, or changes to a new weather regime are in the offing, or
whether I forecast an extension to a regime, appears to make no
difference. If I see consistency and cross-model agreement, my
outcomes stay around 80% correct whatever the time of year, or
whatever the situation that I'm forecasting. Like I say, two days in,
this forecast looks less secure and the MetO are also going for an
unsettled end to September and an unsettled start to October, on their
6-15 day tea-break precis. They could be correct, but I'll judge that
on the 29th.

"UK Outlook for Sunday 26 Sep 2010 to Tuesday 5 Oct 2010:

Sunday should be generally dry, but indications suggest that wet and
windy weather is likely to move into northern and western parts from
Monday and to all parts by Wednesday. The southeast of the UK is
expected to remain driest for longest. Temperatures will initially be
below average for many areas, although should recover to near normal
for the last week of September. However, the odd patch of overnight
ground frost cannot be ruled out, especially early on. This unsettled
spell is likely to continue into the start of October with further
periods of rain or showers. Generally becoming quite breezy with
strong winds possible at times, and a risk of gales in exposure,
especially in the northwest. Temperatures near or slightly above
normal.

Updated: 1203 on Tue 21 Sep 2010"

"Dawlish" wrote in message
news:e72a48b5-eaa7-48a5-ae45-

the MetO are also going for an
unsettled end to September and an unsettled start to October, on their
6-15 day tea-break precis.

I'd like to clear this tea-break" misnomer up once and for all.

The medium range forecaster produces technical guidance out to day 15
overnight. This provides the basis by which the PWS forecaster drafts the
6-15 day forecast you see on the web page. The format, length and forecaster
time spent on this forecast are strictly set out in a customer service
agreement - in this case with the PWS Customer Group. The guidance is then
updated during the morning by the deputy chief and discussed with the PWS
forecaster at length before the 6-15 day script is finalised and issued.

Ironically, when I'm team leading it's part of my role to ensure that
forecasters do take their breaks accordingly throughout the shift and in an
often busy 24/7 forecasting environment that's no easy task.

Jon.

On 21 Sep, 19:39, Dawlish wrote:

I'm right 80% of the time Will, over 90 different forecasts at all
times of the year.

No, you're not right 80% of the time, Paul.You're right 80% of the
time when you decide the time is right to forecast. A subtle, but
enormous difference.

Richard