For the last few days, the charts for the weekend have been suggesting
pressure close to 1024mb for the south, with a few weak fronts,
suggesting a couple of days of dry if rather cloudy conditions.
Today's newspaper forecast for central southern England said almost
exactly that.

So I went out today expecting the chance of any rain more than a few
drops in the wind being almost 0 %. So I was completely unprepared for
the two-hour spell of moderate and at times heavy rain which passed
over the Haslemere area early afternoon...

The current analysis (18BST) still suggests high pressure with
embedded fronts. So why was this front so active? What is so very
ironic is that the cold front ahead of the northerly on Thursday
passed through with almost no rain at all! I actually expected
Thursday to be a wet day but it was dry...

Ironically again it was the warm front of the system which produced
the rain. The cold front (I presume this has gone through now)
produced no rain at all but did cause a noticeable change from misty
murky conditions (early evening) to clear skies (now). And the rain on
the warm front was typical of that of a *cold* fromt: it seemed
convectional, stair-rod like at times, short duration and stopped
suddenly after the heaviest phase towards the end.

I suppose the moral of this is to expect heavy rain whenever there are
fronts in the vicinity, even if pressure is high....

Nick

"Nick Whitelegg" wrote in message
m...
For the last few days, the charts for the weekend have been suggesting
pressure close to 1024mb for the south, with a few weak fronts,
suggesting a couple of days of dry if rather cloudy conditions.
Today's newspaper forecast for central southern England said almost
exactly that.

snip

I suppose the moral of this is to expect heavy rain whenever there are
fronts in the vicinity, even if pressure is high....

Nick

I wouldn't ! I'm puzzled by the forecast in your newspaper, out of interest
can you reveal which paper and who provides the forecast ? There was some
uncertainty on Friday with regard to the positioning and intensity of the
rain on Saturday but by the time the 12Z model runs were in it looked quite
probable that the south would see a period of rain, most likely from late
morning and through the afternoon. In the event it came through faster and
cleared earlier than expected on Friday.

Jon.

On Sun, 26 Sep 2004 01:16:42 +0100, "Jon O'Rourke"
wrote:

"Nick Whitelegg" wrote in message
om...
For the last few days, the charts for the weekend have been suggesting
pressure close to 1024mb for the south, with a few weak fronts,
suggesting a couple of days of dry if rather cloudy conditions.
Today's newspaper forecast for central southern England said almost
exactly that.

I suppose the moral of this is to expect heavy rain whenever there are
fronts in the vicinity, even if pressure is high....

I wouldn't ! I'm puzzled by the forecast in your newspaper, out of interest
can you reveal which paper and who provides the forecast ? There was some
uncertainty on Friday with regard to the positioning and intensity of the
rain on Saturday but by the time the 12Z model runs were in it looked quite
probable that the south would see a period of rain, most likely from late
morning and through the afternoon. In the event it came through faster and
cleared earlier than expected on Friday.

The BBC TV forecasts late on Friday evening certainly got it right - I
remember groaning when I realised that Saturday afternoon and evening
were probably a write-off for the outdoor activities I had planned.

However... I simply re-scheduled for Sunday. That one better be right,
too!

--
Dave
Fareham Hants.

"Jon O'Rourke" wrote in message ...
"Nick Whitelegg" wrote in message
m...
For the last few days, the charts for the weekend have been suggesting
pressure close to 1024mb for the south, with a few weak fronts,
suggesting a couple of days of dry if rather cloudy conditions.
Today's newspaper forecast for central southern England said almost
exactly that.

snip

I suppose the moral of this is to expect heavy rain whenever there are
fronts in the vicinity, even if pressure is high....

Nick

I wouldn't ! I'm puzzled by the forecast in your newspaper, out of interest
can you reveal which paper and who provides the forecast ?

Was the Telegraph (BTW in case anyone incorrectly tries to guess my
political persuasion :-) it was just the one with the most convenient
forecast to look at [on the back page]).

Still puzzled as to why such significant rain should fall when
pressure was 1020-1024mb. Obviously the forecasters know something
which can't be gleaned from the pressure charts....

Nick

Dave Ludlow wrote in message
The BBC TV forecasts late on Friday evening certainly got it right - I
remember groaning when I realised that Saturday afternoon and evening
were probably a write-off for the outdoor activities I had planned.


I've just seen the radar animation for this "event" and I'm very
puzzled. In the northwest and north Midlands, the rain band was much
narrower and more fragmented, and less intense - despite lower
pressure up there. They got what I would have expected from the
pressure charts.

The rain seemed to intensify as it moved southeast into higher
pressure, and to my amazement the most intense area was actually west
of where I was, over Dorset, Somerset etc, where the pressure was
around 1024mb - I certainly expected the southwest and western Wessex
to have a dry day. Only Cornwall was out of the rain. A most bizarre
event - I have to admit that due to the vagueness of published
forecasts I normally go on the charts and am normally right but this
time was wrong :-(

As an aside, the times when my own chart-based forecasts are most
often wrong a

a) Cold fronts bringing in northerlies. I generally expect it to chuck
it down but frequently these pass through with almost no rain at all,
at most light showers, even with relatively low pressure.

b) Cold fronts bringing in westerlies after a hot spell, again these
are often associated with very little rain - I frequently expect
thunder out of these.

Nick

Nick Whitelegg wrote in message ...
Dave Ludlow wrote in message
The BBC TV forecasts late on Friday evening certainly got it right - I
remember groaning when I realised that Saturday afternoon and evening
were probably a write-off for the outdoor activities I had planned.


I've just seen the radar animation for this "event" and I'm very
puzzled. In the northwest and north Midlands, the rain band was much
narrower and more fragmented, and less intense - despite lower
pressure up there. They got what I would have expected from the
pressure charts.

The rain seemed to intensify as it moved southeast into higher
pressure, and to my amazement the most intense area was actually west
of where I was, over Dorset, Somerset etc, where the pressure was
around 1024mb - I certainly expected the southwest and western Wessex
to have a dry day. Only Cornwall was out of the rain. A most bizarre
event - I have to admit that due to the vagueness of published
forecasts I normally go on the charts and am normally right but this
time was wrong :-(

As an aside, the times when my own chart-based forecasts are most
often wrong a

a) Cold fronts bringing in northerlies. I generally expect it to chuck
it down but frequently these pass through with almost no rain at all,
at most light showers, even with relatively low pressure.

b) Cold fronts bringing in westerlies after a hot spell, again these
are often associated with very little rain - I frequently expect
thunder out of these.

Nick

Nick, man cannot live by pressure and fronts alone. That is why we have NWP
models and satellite images. Rain occurs due to moist air being lifted high
enough to permit saturation and growth of precipitation particles. Pressure by
itself has nothing to do with that process. In fact pressure should be viewed as
a *result* of moist dynamical and thermodynamic processes. Have you thought
about the possibility that if it hadn't rained then pressure could well have
been higher ?

Will.
--

" A cup is most useful when empty "
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