In message , Waghorn
writes
I think a lot of it might be down to "luck" Jack.
..........
hit-and-miss nature of this type of weather.

--
Chris

Actually in this case a good forecast may not have been down to luck.As
outlined by Joe and in the
Estofex alert all the ingredients for forecasting the location and
severity of the storms seem to
have become available during the day.
I think credit should be given for the advances in 'nowcasting' storm
development in fields of
observing systems,modelling and conceptual understanding.
Of course there's a way to go and it can all be ruined in the last step
of communication to the
public.For tastes of the state of the art see eg

Precipitation diagnostics for a high resolution forecasting system.
This is the stage 3 report from
the Storm Scale Modelling project by Nigel Roberts 2003
Stage 2 report from the Storm-scale numerical modelling project by
Nigel Roberts
Stage 1 report from the Storm-scale numerical modelling project by
Nigel Roberts
at-
http://www.met-office.gov.uk/researc...ers/technical_
reports/fr.html
and
http://www.env.leeds.ac.uk/csip/oct1...entations.html

I'm not convinced that it was well forecast on this occasion. All the
emphasis on the forecasts I saw during the morning was that it was the
SE of England that would catch the torrential downpours, explicitly
during the evening rush hour. That didn't happen. The relevant batch of
storms passed further to the east. The forecast weather did occur, but
it occurred in the wrong place!

I hope that the science of meteorology doesn't advance in my lifetime to
the point where the time and place of thunderstorms can be accurately
predicted. That capability would remove a great deal of the wonder from
the subject.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles
England

In message , Joe Hunt
writes

"Waghorn" wrote in message
...
I think a lot of it might be down to "luck" Jack.
..........
hit-and-miss nature of this type of weather.

--
Chris

Actually in this case a good forecast may not have been down to luck.As
outlined by Joe and in the
Estofex alert all the ingredients for forecasting the location and
severity of the storms seem to
have become available during the day.
I think credit should be given for the advances in 'nowcasting' storm
development in fields of
observing systems,modelling and conceptual understanding.

Hi David,

I think something that should be brought to people's attention is the issue
of Flash warnings that are a prime example of the nowcasting techniques the
MetO adopt at such times. These were issued readily yesterday for all the
regions concerned.

It's a pity that there's no automatic e-mail distribution list for these
warnings like there is for similar warnings in the USA. I raised this
recently with UKMO but the response was that it would cost too much
money.

However accurate and timely the Flash warnings may be they have value
only if they very promptly get into the hands of individuals who can
make decisions based on them. Posting the warnings on a web page is not
an efficient means of distribution as it relies on potential users
checking to see whether or not any warnings have been issued. An e-mail
distribution list is a much more reliable means of communication.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles
England

I'm not convinced that it was well forecast on this occasion. All the
emphasis on the forecasts I saw during the morning was that it was the
SE of England that would catch the torrential downpours, explicitly
during the evening rush hour. That didn't happen. The relevant batch of
storms passed further to the east. The forecast weather did occur, but
it occurred in the wrong place!

Didn't follow things during the day,so I can't comment categorically.However,my post mortem of the
0Z GFS run,output from the Meteoswiss ,NMM and Estofex seem to have got it pretty much right.Was it
just the UKMO mesoscale that had a bad run?

I hope that the science of meteorology doesn't advance in my lifetime to
the point where the time and place of thunderstorms can be accurately
predicted. That capability would remove a great deal of the wonder from
the subject.
Norman.

Well,let's hope it's a long time coming ;-).Big claims have been made,but despite the advances there
are still challenges,


--
regards,
david
(add 17 to waghorne to reply)

I agree with a Julian Mayes post about the lack of an appropriate
presentation of such a storm system on television stations. The kind of
debate that is being discussed here could be covered on a weather channel or
a hybrid of it. i.e. combine travel(roads and rail etc), air port info etc
with weather as it happens.
A glance at the radar and Sferic information during the afternoon clearly
showed the favoured areas for development. Yet forecasts continually
mentioned the Southeast and as Julian stated this prevailed well into the
evening. At a key time yesterday meteorologically the News 24 Channel missed
two broadcasts on the half hour and hour due to a live broadcast featuring
the Prime Minister answering questions set by journalists. Yes he should
answer questions but perhaps it could be on BBC 2 etc.
There are sacrosanct areas of the Media. Not even nuclear war would shift
the Archers from being broadcast.

Of course what is needed is a Weather channel. Information is available,
there is an interest but it is regarded by the top media moguls as not being
"sexy" rather "anorakish". Perhaps though it could be combined , yes a `Big
Brother Weather Channel'.
Ian Currie- Coulsdon.
www.Frostedearth.com


"Joe Hunt" wrote in message
...

"Waghorn" wrote in message
...
Widespread showers can and indeed often do apparently crop up more or
less
randomly. But clearly it cannot be a simple random process. Factors
such
as convergence, locally higher dewpoints, etc must be at work.

Jack,
haven't followed closely as rather busy but-
I have saved some streamlines from the GFS and NMM 22km from y'day and
they clearly show convergence
in the warm,moist plume from the south (let me know if want a look).I
imagine the MO mesoscale
model wld have done an even better job.Engagement of the slow moving
trough in the west with this
plume and convergence triggered the heavy showers ,wind shear wld have
been enough to turn the cold
pools away from the updrafts and allow a degree of organisation into a
smallish Mesoscale Convective
System.This shows a comma like appearance in radar imagery later in it's
lifecycle.
I wonder if CSIP were up for this-
http://www.env.leeds.ac.uk/csip/
were up for this.Anybody Know?

Hi David/Jack,

It certainly was an interesting event. The showers around the Bristol area
were indeed triggered through dynamic ascent ahead of the upper trough
moving E through the strong SW flow aloft. Winds were sampled at 75-80kts
at
300mb on many 22/11Z ascents along with considerable speed shear and
directional shear in the lowest layers. A closer look at the 12Z WV images
and jet stream maps shows the storm complex lying in the right entrance of
a
jet streak, an area of maximum acceleration of air, further inducing
ascent.
It is these dynamic features that helped maintain the complex for such a
long period and hence an MCS may have formed.

http://www.sat.dundee.ac.uk/pdus/BW/...21200BW1_g.jpg (12Z WV)
http://www.sat.dundee.ac.uk/pdus/BW/...21800BW1_g.jpg (18Z WV - jet
streak visible Manchester-Cornwall)

Also of note from the above is the developing wave that ran along the cold
front moving ENE which gave NW areas some heavy rain for a few hours (3hrs
of moderate showery rain at EGNH Blackpool). An associated dry slot (PV
max)
ushering the storms NE and providing further ascent.

The following soundings show the conditional instability in the atmosphere
at 11Z yesterday. Inversions at between 650-700hPa cap the energy at the
surface which is fuelled by reservoirs of moisture (WBPT 16degC), however
it
is at Watnall where a large amount of potential instability was probably
released when the inversion was broken.


http://weather.uwyo.edu/cgi-bin/soun...F%3ASKEWT&YEAR
=2004&MONTH=7&FROM=2212&TO=2212&STNM=03354&STNN=No ttingham%2FWatnall
(22/11Z Watnall)


http://weather.uwyo.edu/cgi-bin/soun...F%3ASKEWT&YEAR
=2004&MONTH=7&FROM=2212&TO=2212&STNM=03743&STNN=La rkhill
(22/11Z Larkhill)

The lack of home-grown thunderstorms in the SE was most likely due to
subsidence from both the "MCS" over central UK and the area of
thunderstorms
that skimmed the far SE coast.

In short, convergence (which has already been covered), several forcing
elements from aloft, abundant moisture, surface heating all seem to have
played a part. Bristol may have been a foci of moisture due to surface
convergence and hence all the "ingredients" occurred here first.

What is interesting is the cells that spawned over the
Cambridgeshire/Rutland area on the E side of the storm, flanking lines ?

Joe

"Ian Currie" wrote in message
. uk
Snips

A glance at the radar and Sferic information during the afternoon clearly
showed the favoured areas for development. Yet forecasts continually
mentioned the Southeast and as Julian stated this prevailed well into the
evening.

Well they were right then given the storm that developed over London in
the evening and moved across East Anglia. However I agree that more
frequent live 'nowcasts' would help show what is currently happening and
could have placed the emphasis on the intense TS occuring over the
Midlands/NE England as well as mentioning what could develop later.

I must admit I hardly watch New24 weather anymore because of this :-(

Jon.





--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

"Joe Hunt" wrote in message
...

Snip
Bristol may have been a foci of moisture due to surface
convergence and hence all the "ingredients" occurred here first.

Localised convergence (among other factors excellently detailed by Joe) was
evident at 1300Z and quite probably the key to the activity that developed
near Bristol and extended NE as an apparent MCS.

The 1300Z streamline analysis/conveyance can be seen here :-
http://www.metbrief.com/13z.gif

Jon.

"Joe Hunt" wrote in message
...

Snip
Bristol may have been a foci of moisture due to surface
convergence and hence all the "ingredients" occurred here first.

Localised convergence (among other factors excellently detailed by Joe) was
evident at 1300Z and quite probably the key to the activity that developed
near Bristol and extended NE as an apparent MCS.

The 1300Z streamline analysis/convergence can be seen here :-
http://www.metbrief.com/13z.gif

Jon.