On Apr 19, 9:53*am, "Will Hand" wrote:
"Dawlish" wrote in message

...
On Apr 8, 1:14 pm, Dawlish wrote:





Well, there you go.The possible warmth has continued for 5 runs, I can
now be 75-80% certain of this:

By 18th April at T240, the effects of the first warm plume of the year
will be being felt in Southern England. Temperatures on the 17th and
18th of April will peak above 18C and may well be higher. Winds around
this time will be from a Southerly quadrant and the air will have had
its source in North Africa. This air could well be unstable enough to
bring the possibility of heavy, perhaps thundery showers. If the
showers stay away, Southern England, at least, will have some
pleasant, warm conditions for April.

It can never be a higher confidence forecast than 75-80%, as my
success from the past is about 78%. It's not a certain forecast, as
certainty doesn't come in to forecasting. See how it goes.

Paul

I always return to any forecast I make, be it good, or bad!

OK a hopeless forecast. This one fell into the 20-25% of faliures and
it ranks as a stinker amongst those (Euro stinker? No muck on the
ground in the rain though in Devon!) . It's not even a near miss and
it ranks on the abysmal level of the Cold Northerly I forecast at
Easter 2007 (remember that glorious, warm sunny weather at an Easter
which now sits in the warmest April for 350+ years?)

The reason was a combination of a Southerly diving jet, producing cold
uppers and an associated lee depression which is likely to track W to
E along the channel and across Northern France. It has stymied any
development of that warm plume that was shown on the gfs for a few
days, in one form or another, 10 days ago. This was compounded by*
the Northern blocking of Early April continuing and sitting there over
Iceland, like a giant high pressure toad, squatting with its heavy
haunches and putting up an impenetrable wall of toady atmosphere
against the release of my predicted North African plume. OK,
stretching a metaphor, but I hope you get the picture.

Maybe I've got the first plume right, at 10 days, on the max temp
record thread!

Paul

* Does high pressure at our latitudes result from the track of the
jet, or does it alter the jet's path. Has this jet been forced South
by an anticyclone which stretches from ground level to the 200mb hpa
level, or did it form as a result of the jet tracking south? It's a
chicken and egg scenario that I've always found hard to interpret. In
this case, I'd go with the high developing and the jet being forced
around it, but I could be wrong! Any clues, anyone?

=====

NEW POST

I cannot quote your previous text as Outlook Express does not recognise the
format you used.

It is the jet, itself arising from temperature variations, that forms the
high pressure regions in our latitudes. Don't foget the global circulation
Hadley cells that help form the various jets in the first place, which
themselves arise from insolation and the earth's rotation. And then there
are the Rossby waves affected by major mountain structures like the Rockies
which meander around and alter the jet streams. The atmosphere should always
be thought of as a system as per Systems Theory. Isolating various parts is
good for understanding physics etc and causes of weather such as rain,
thunder etc, but you need to treat it as a whole to get rid of chickens and
eggs.

Re your forecast. I too was interested in that southerly at T+240. I was
tempted to say something but my instincts (backed up by ensembles) told me
to keep quiet. I've gone for a warm and sunny weekend next weekend instead!
We all make bad forecasts, nobody is perfect, not even WL :-)

No pongs up here, I had a good sniff last night but all I could smell was
wet grass! A bit of a pong yesterday morning as I reported but very very
faint and there a lot of cess pits anyway in these upland parts :-)

Cheers Paul,

Will
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Thanks Will, that sounds highly sensible and the textbook theory is
that the jet causes the surface pressure systems and it is good to be
reminded that it is a system that cannot be broken into its component
parts and there is no chicken and egg, really........... however, it
still bugs me! This is such a weak Southerly jet in this particular
Rossby wave and the I think the blocking anticyclone (and now it is
memory, which is never a good thing on which to base any scientific
speculation) formed before the jet tracked southwards. I'm sure you
are right and I know the theory.............but it still makes me
think!

Paul

"Dawlish" wrote in message
...
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! *))

Spring NOT coming
Yes I knew you'd say that its been said a multitude of times about the
interesting British climate. Bahrain? a bit extreme however. Well ok its
interesting yes but all I ever seem to do is scan the forecasts for some
nice settled weather certainly at this time of the year (I dont do this from
November to March) until say November when you just cant get outside anymore
without loads of heavy incumberant clothing then theres the dark and short
days so miserable they are. Pessimistic I am and theres only 75 days left
until Midsummer with the prospect of there not being one then its all
downhill again. Anyway this year I am retiring which is about time an I know
one thing I wont be around for 2008/9 Nov - March in the UK I'm off
somewhere i dunno were yet but i'm off south - leave you all too the
wonderful british climate.
Dave R.

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.