On 7 Apr, 16:01, Dawlish wrote:

The operational run is the one that the computer
has selected as the most likely to achieve outcome and even that is
often hopelessly wrong at 10 days and each single operational run has
a very low probability of achieving outcome.

It's very difficult to interpret the output from the ensembles in the
GFS when they're run at a different resolution to the operational run.
On occasions the operational run can be completely different to the
ensembles which renders the whole thing useless and just highlights
the role of model resolution on forecast accuracy !

Richard

On Apr 7, 5:26*pm, Richard Dixon wrote:
On 7 Apr, 16:01, Dawlish wrote:

The operational run is the one that the computer
has selected as the most likely to achieve outcome and even that is
often hopelessly wrong at 10 days and each single operational run has
a very low probability of achieving outcome.

It's very difficult to interpret the output from the ensembles in the
GFS when they're run at a different resolution to the operational run.
On occasions the operational run can be completely different to the
ensembles which renders the whole thing useless and just highlights
the role of model resolution on forecast accuracy !

Richard

Absolutely true. Thank you Richard. The 4, daily, gfs runs are of
differing resolution and are also run with different perameters,
That's why the coincidence of 5 consecutive runs producing very
similar output is impossible for me to ignore.

Paul

On Apr 7, 1:01*pm, Dawlish wrote:
On Apr 7, 12:08*pm, Dawlish wrote:





On Apr 7, 11:46*am, "Dave R." wrote: "Dawlish" wrote in message

....
Not fine warm and settled Dave, just warmer. It certainly looks
unsettled during the early part of next week, with high pressure -
fine and settled - only after T300. Anything there is, of course,
unlikely.

Neither is that forecast of warmer than average conditions a forecast;
just yet.

Paul

*I hate this country.

Dave R.

I have to disagree there! It's one of the most interesting in the
world for weather watching; maybe THE most interesting. Just imagine
being in Bahrain! Mind you, if you hate this country, there are a
whole load of others that you could hate living in! *))

Another run with hints of a warming, but a subtly different set-up and
the outside chance of a plume heading our way.

http://www.wetterzentrale.de/pics/Rtavn1802.png

Still not enough confidence for any kind of forecast at T240. This
mildness has come in under my radar. Some warmth would be very
welcome, though.

Paul- Hide quoted text -

- Show quoted text -

2 runs with a plume and the possibility of some warm April weather at
the end of next week. If it is still there tomorrow lunchtime. It
would be worth a confident forecast. If it disappears into the
computer ether....we'll just have to wait longer for that spring
warmth. I've only low confidence in this at present. The warmth shown
in the 06z a week hence is not there to the same degree on the 12z.
Certainly an improving picture, but not one which i would be confident
about at T240 yet.

Paul

"Dawlish" wrote in message
...

The ensembles provide a good tool to 7 days, but why use ensembles to
give you a forecasting tool when each ensemble has so little chance of
being correct at 10 days?

Perhaps interesting to note that ensemble based products are now routinely
used in short period forecasting as well as the medium range.

Jon.

"Dawlish" wrote in message
...

The operational run is the one that the computer
has selected as the most likely to achieve outcome

Is it ? I though it was essentially just another model run albeit at a
higher resolution compared to the ensemble, and even the operational run
lowers in resolution at T+180 IIRC.

Either way the GFS appears to be getting all the headlines in this thread
when the best model in terms of medium range deterministic and ensemble
output is ECMWF, IMHO of course but also according to
http://wwwt.emc.ncep.noaa.gov/gmb/ST.../aczhist6.html

Jon.

PS I thought 18°C in Exeter was too warm last Thursday, roll on autumn !

Jon O'Rourke wrote:

"Dawlish" wrote in message

...

The operational run is the one that the computer
has selected as the most likely to achieve outcome

Is it ? I though it was essentially just another model run albeit at a
higher resolution compared to the ensemble, and even the operational
run lowers in resolution at T+180 IIRC.

Either way the GFS appears to be getting all the headlines in this
thread when the best model in terms of medium range deterministic and
ensemble output is ECMWF, IMHO of course but also according to
http://wwwt.emc.ncep.noaa.gov/gmb/ST.../aczhist6.html

Jon.

PS I thought 180C in Exeter was too warm last Thursday, roll on
autumn !


The GFS ensemble gets the headlines on here because the ECMWF ensemble
output isn't put into the public domain as far as I am aware.

Your PS strikes a chord!

Norman
--
Norman Lynagh
Chalfont St Giles, Buckinghamshire
85m a.s.l.
(remove "thisbit" twice to e-mail)

On Apr 7, 10:47*pm, "Norman" normanthis...@thisbitweather-
consultancy.com wrote:
Jon O'Rourke wrote:
"Dawlish" wrote in message

...

The operational run is the one that the computer
has selected as the most likely to achieve outcome

Is it ? I though it was essentially just another model run albeit at a
higher resolution compared to the ensemble, and even the operational
run lowers in resolution at T+180 IIRC.

Either way the GFS appears to be getting all the headlines in this
thread when the best model in terms of medium range deterministic and
ensemble output is ECMWF, IMHO of course but also according to
http://wwwt.emc.ncep.noaa.gov/gmb/ST.../aczhist6.html

Jon.

PS I thought 180C in Exeter was too warm last Thursday, roll on
autumn !

The GFS ensemble gets the headlines on here because the ECMWF ensemble
output isn't put into the public domain as far as I am aware.

Your PS strikes a chord!

Norman
--
Norman Lynagh
Chalfont St Giles, Buckinghamshire
85m a.s.l.
(remove "thisbit" twice to e-mail)- Hide quoted text -

- Show quoted text -

True, the gfs gets the headlines because it is the only model updated
4x per day - which is why I chose it for my forecasting. I'm well
aware nof the NOAA comparisons and my frustrations with being able to
find nothing, anywhere that goes beyond their 5-day-max horizon, just
added to my overall frustrations with the lack of accurate forecasting
at T240 (10 days). The ECM verifies, most of the time, as the best
forecasting model at 5 days, but even with the ECM, accuracy in
forecasting temperatures has varied between 0.91 and 0.72 over this
last month, with the mean accuracy being 0.847. Granted, this is
higher than the other 3 models that they evaluate (gfs in second place
with 0.793), but we are talking about the model being wrong about 15%
of the time even and only, at 5 days.

There are no published figures beyond this, though the fact that no-
one bothers to produce them, or comment upon them, has always
suggested to me that the accuracy falls off markedly between 5 days
and 10 days. The Met Office's lumping of all medium-term forecasts
into the 6-15 day range and the coining of the Internet terms; "FI"
and the model watcher's mantra; "beyond the reliable timeframe",
which is trotted out whenever someone disagrees with anything that
anyone else says at T144+, would support the assertion that accuracy
falls sharply. ECM may well be more accurate, but what level of
accuracy are we talking about? All models around 50%? Less?

So, how do we forecast with any believable accuracy at 10 days and how
do we measure it? Is it actually possible with present day forecasting
and model limitations?

Paul

On Apr 7, 1:58*pm, "Norman" normanthis...@thisbitweather-
consultancy.com wrote:
Dave R. wrote:

Another run with hints of a warming, but a subtly different set-up and
the outside chance of a plume heading our way.

http://www.wetterzentrale.de/pics/Rtavn1802.png

Still not enough confidence for any kind of forecast at T240. This
mildness has come in under my radar. Some warmth would be very
welcome, though.

Paul

Wow that looks fantastic I hadn't seen that one at the wetterzentrale
site and only have to wait until the 12th! fingers crossed and thks
Dave R.

The 06Z GFS ensemble mean show 850 mb temps rising only to around
average in the south of the British Isles, implying daytime max temps
probably around 10-12c. The 850mb ensemble for London can be found at

* * * * * * *http://85.214.49.20/wz/pics/MT8_London_ens.png

The 06z GFS operational run is on the warm side of the ensemble mean.

Norman
--
Norman Lynagh
Chalfont St Giles, Buckinghamshire
85m a.s.l.
(remove "thisbit" twice to e-mail)- Hide quoted text -

- Show quoted text -

ECM now seems to be showing those SW winds at 8 days. Darren has
highlighted that in his analysis this morning. Excellent agreement in
the ensembles to 6 days out, then spaghetti. It illustrates well what
I was saying in my last post about forecast accuracy falling off
quickly from 5 days to 10 days out.

Nothing markedly warm in today's output, but a warming, nevertheless.
It will feel springlike in those, now likely, mild South-Westerlies in
the early part of next week. Nothing particularly settled either,
Those unstable, flabby areas of low pressure could give some soakings
in slow-moving showers. If the present forecast lows move East, we'd
be back into cool Northerlies and North-westerlies.

In April, the onset of "spring" often proves to be temporary though.
Hints of cooler again at the edge of reality!

Paul

PS 18C in Exeter, guys!! I was there in that 18C (ish) and the smiles
on the faces of the shoppers were really nice to see. 18C and sunny,
in April, is most people's idea of perfect weather! I'll side with
that majority and say that Autumn can stay as a spectre on the distant
horizon, when looking from the perspective of April!

In article
,
Dawlish writes:
snip
The ECM verifies, most of the time, as the best
forecasting model at 5 days, but even with the ECM, accuracy in
forecasting temperatures has varied between 0.91 and 0.72 over this
last month, with the mean accuracy being 0.847. Granted, this is
higher than the other 3 models that they evaluate (gfs in second place
with 0.793), but we are talking about the model being wrong about 15%
of the time even and only, at 5 days.

That raises the question of how wrong does it have to be to be flagged
as wrong? If we don't know that, then those statistics don't tell us
very much. To complicate matters, there are at least two factors to be
considered when determining whether the model is "correct": the size of
the discrepancy between forecast and actual temperature, and the
proportion of the area being forecast for over which that discrepancy
occurs. And are we talking about surface temperatures, which are the
ones of prime concern to the layman, or - as I suspect - 850mb
temperatures?
--
John Hall
"If a man will begin with certainties, he shall end in doubts;
but if he will be content to begin with doubts,
he shall end in certainties." Francis Bacon (1561-1626)

On Apr 8, 9:40*am, John Hall wrote:
In article
,*Dawlis h writes:

snip

The ECM verifies, most of the time, as the best
forecasting model at 5 days, but even with the ECM, accuracy in
forecasting temperatures has varied between 0.91 and 0.72 over this
last month, with the mean accuracy being 0.847. Granted, this is
higher than the other 3 models that they evaluate (gfs in second place
with 0.793), but we are talking about the model being wrong about 15%
of the time even and only, at 5 days.

That raises the question of how wrong does it have to be to be flagged
as wrong? If we don't know that, then those statistics don't tell us
very much. To complicate matters, there are at least two factors to be
considered when determining whether the model is "correct": the size of
the discrepancy between forecast and actual temperature, and the
proportion of the area being forecast for over which that discrepancy
occurs. And are we talking about surface temperatures, which are the
ones of prime concern to the layman, or - as I suspect - 850mb
temperatures?
--
John Hall
* * * * * *"If a man will begin with certainties, he shall end in doubts;
* * * * * * but if he will be content to begin with doubts,
* * * * * * he shall end in certainties." * * * Francis Bacon (1561-1626)

Very true John, I agree. None of what you (rightly) say applies at T
+240, however. We can only judge how accurate the models are there by
proxy; eg the lack of published figures, the lack of Met Office
clarity in forecasting at that range for the public and the general
"not reliable" feeling of so many Internet commentators.

NOAA's does produce a range of stats covering several variables, which
can be combined. Try:

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/

.....and click the "go" buttons.

Paul