I was wondering how far ahead the GFS pressure, temperature & rainfall
charts can be relied upon. The reason for the question is that we're
off on our Holidays to Switzerland in August and the Gfs charts seem to
be suggesting a much improved outlook which quite frankly i'm
desperately hoping is correct. I had read somewhere that the charts up
to +240 can be considered fairly accurate but become rather fanciful
after that.

If someone could advise me please that would be great.

Many thanks

In article ,
David Gartrell writes:
I was wondering how far ahead the GFS pressure, temperature & rainfall
charts can be relied upon. The reason for the question is that we're
off on our Holidays to Switzerland in August and the Gfs charts seem to
be suggesting a much improved outlook which quite frankly i'm
desperately hoping is correct. I had read somewhere that the charts up
to +240 can be considered fairly accurate but become rather fanciful
after that.

I think that's over-optimistic. The accuracy normally starts to tail off
after 5-6 days, and is usually quite low by 10 days (ie +240). Pressure
will be most accurate, because small inaccuracies in the derived
pressure pattern, and the consequent position of fronts, can have a big
impact on temperature and, in particular, rainfall.

You can get a better idea by seeing if the three main models, GFS, ECMWF
and UKMO are consistent with each other and from run to run. If the 06Z
GFS run is radically different from the 00Z, and then the 12Z is
different again, that suggests that the outcome is likely to be on a
knife-edge.
--
John Hall

"I don't even butter my bread; I consider that cooking."
Katherine Cebrian

"David Gartrell" wrote in message
...
I was wondering how far ahead the GFS pressure, temperature & rainfall
charts can be relied upon.

No more than 5 or 6 days and even then you'd be better off looking at the
MetO GM and EC. They're simply better models, IMHO.

Jon.

On Jul 28, 9:19*pm, David Gartrell wrote:
I was wondering how far ahead the GFS pressure, temperature & rainfall
charts can be relied upon. *The reason for the question is that we're
off on our Holidays to Switzerland in August and the Gfs charts seem to
be suggesting a much improved outlook which quite frankly i'm
desperately hoping is correct. *I had read somewhere that the charts up
to +240 can be considered fairly accurate but become rather fanciful
after that.

If someone could advise me please that would be great.

Many thanks

That very much depends David. I maintain that there are occasions when
it is possible to forecast using the gfs at 10 days. I've proved that
with a 78% success rate, over 89 forecasts over 5 years, forecasting
at those particular times. I've only issued those forecasts in
circumstances, where consistency in the gfs output agrees with ECM
(and other output). Determining those times is not easy, I can assure
you.

The rest of the times, inconsistency and lack of agreement makes
forecasting impossible - and that's the majority of the time, IMO.

I couldn't comment on the Alps' weather over the next 10 days, sorry;
I haven't been watching the models for that area, only the UK.
Whatever it presently shows may, or may not, come to outcome, but
you'd only know to trust it if the output had been consistent and
agrees with other models over the last 24 hours - even then, you are
only loolking at being correct 3 times out of 4.

Forecasting at 10 days is a mug's game. It's impossible with regular,
daily forecasts and even the MetO hardly bothers. I always think that
their 6-15 days forecast (from which you may be able to divine the
forecast at 10 days, on occasions) is written in the tea break, in
between doing crossord clues. You'd be better tuning in closer to your
hols. 5/6 days is pretty accurate, as evidence by NASA's model success
monitoring . 7 days is still reasonable, but after that, outcome
success plummets.

Hope you enjoy your holiday. I remember a visit to the Bernese
Oberland in August and skiing on the Jungfrau glacier. Magnificent.
Snow-blind in the tunnels walking to the train, but still magnificent!
Have lunch in the Schilthorn revolving restaurant. Again, truly
magnificent! The view of a lifetime! You slowly turn to see the
Jungfrau, Monch and the Eiger pass, whilst eating lunch (which was
amazingly crap! - but who cares! Most of it ended up dribbled down
your chin as you concentrated on the panorama out of the window).

I'm sorry

On Jul 28, 9:40*pm, John Hall wrote:
In article ,
*David Gartrell writes:

I was wondering how far ahead the GFS pressure, temperature & rainfall
charts can be relied upon. *The reason for the question is that we're
off on our Holidays to Switzerland in August and the Gfs charts seem to
be suggesting a much improved outlook which quite frankly i'm
desperately hoping is correct. *I had read somewhere that the charts up
to +240 can be considered fairly accurate but become rather fanciful
after that.

I think that's over-optimistic. The accuracy normally starts to tail off
after 5-6 days, and is usually quite low by 10 days (ie +240). Pressure
will be most accurate, because small inaccuracies in the derived
pressure pattern, and the consequent position of fronts, can have a big
impact on temperature and, in particular, rainfall.

You can get a better idea by seeing if the three main models, GFS, ECMWF
and UKMO are consistent with each other and from run to run. If the 06Z
GFS run is radically different from the 00Z, and then the 12Z is
different again, that suggests that the outcome is likely to be on a
knife-edge.
--
John Hall

* * * * * * "I don't even butter my bread; I consider that cooking."
* * * * * * * * * * * * * * * * * * * * * * * * * *Katherine Cebrian

I didn't read John's post before writing mine, honest ref!

"David Gartrell" wrote in message
...
I was wondering how far ahead the GFS pressure, temperature & rainfall
charts can be relied upon. The reason for the question is that we're off
on our Holidays to Switzerland in August and the Gfs charts seem to be
suggesting a much improved outlook which quite frankly i'm desperately
hoping is correct. I had read somewhere that the charts up to +240 can be
considered fairly accurate but become rather fanciful after that.

If someone could advise me please that would be great.

Many thanks



Well in my humble experience over a decade now, I find the various models
are far better in accuracy with bland boring weather that they are with
exceptional scenarios ; especially in the winter.