I'm surprised there aren't any weather warnings out for Sunday. The
latest Fax charts are suggeting a low will develop over England and
areas on the Southern and South-Eastern side of this could be subject
to some fairly intense convection, perhaps leading to thundery
activity, but also some heavy and persistent rain. There will still be
some warm and humid air to the SE of that low and the front that is
likely to spawn it. Keep you eyes on the weather warnings; tomorrow's
nice day (and today's done here) could well be paid for in spades in
the South.

Further afield; the Atlantic looks stalled. The gfs has a low sitting
over us for a week, funnelling warm air Northwards through Eastern
Europe and into Scandinavia and even into the Russian Arctic. After
that, pressure is forecast to rise over Western Russia. Possible May
Easterlies for the UK? Paul Simons writes about exactly that in The
Tombs today and talked about the NW of Scotland sometimes having the
best of the UK weather at this time of year, if the Atlantic does
completely stall, allowing Easterlies to develop.

Paul

On Apr 25, 7:54*pm, Dawlish wrote:
I'm surprised there aren't any weather warnings out for Sunday. The
latest Fax charts are suggeting a low will develop over England and
areas on the Southern and South-Eastern side of this could be subject
to some fairly intense convection, perhaps leading to thundery
activity, but also some heavy and persistent rain. There will still be
some warm and humid air to the SE of that low and the front that is
likely to spawn it. Keep you eyes on the weather warnings; tomorrow's
nice day (and today's done here) could well be paid for in spades in
the South.

Further afield; the Atlantic looks stalled. The gfs has a low sitting
over us for a week, funnelling warm air Northwards through Eastern
Europe and into Scandinavia and even into the Russian Arctic. After
that, pressure is forecast to rise over Western Russia. Possible May
Easterlies for the UK? Paul Simons writes about exactly that in The
Tombs today and talked about the NW of Scotland sometimes having the
best of the UK weather at this time of year, if the Atlantic does
completely stall, allowing Easterlies to develop.

Paul

The Met Office still don't think the rain will be heavy enough for any
kind of advisory/warning tomorrow. The FAX charts still show the
development of that wave depression and I still think there could be
some atmospheric fireworks in some areas and some very heavy rain with
that set-up. The MO has the low centred slightly further North than
yesterday, bringing some central areas of England more into the firing
line.

The 06z gfs shows quite a change from last night's charts from T180
(next Saturday) onwards and now brings us into that warm air that is
forecast to extend right into the Arctic, North of Western Russia and
Scandinavia. Svarlbad as warm as some parts of the UK in early May?
We'll see! It does this by locating the low slightly more West of last
night's location, now allowing the UK to bathe in Southerlies, which
encourage another plume of warm air from North Africa.

Paul

"Dawlish" wrote in message
...

The Met Office still don't think the rain will be heavy enough for any
kind of advisory/warning tomorrow. The FAX charts still show the
development of that wave depression and I still think there could be
some atmospheric fireworks in some areas and some very heavy rain with
that set-up.

Some heavy rain is likely but the detail has varied a bit from run to run
and hence the risk for any particular area is probably deemed less than the
required 40%
http://www.metoffice.gov.uk/weather/..._warnings.html
To a certain extent this is reflected in the 1000Z issue Long TAFs which
indicate moderate rain with no mention of heavy as yet for any particular
airfield (30% risk threshold).

GFS currently has the highest 48 hour totals over parts of northern England,
more especially over the Pennines http://91.121.93.17/pics/Rmgfs48sum.gif

Visible imagery has some deeper looking tops due west of Biscay
http://www.metoffice.gov.uk/satpics/latest_VIS.html

Jon.

On Apr 26, 12:56*pm, "Jon O'Rourke" wrote:
"Dawlish" wrote in message

...

The Met Office still don't think the rain will be heavy enough for any
kind of advisory/warning tomorrow. The FAX charts still show the

development of that wave depression and I still think there could be

some atmospheric fireworks in some areas and some very heavy rain with
that set-up.

Some heavy rain is likely but the detail has varied a bit from run to run
and hence the risk for any particular area is probably deemed less than the
required 40%http://www.metoffice.gov.uk/weather/..._warnings.html
To a certain extent this is reflected in the 1000Z issue Long TAFs which
indicate moderate rain with no mention of heavy as yet for any particular
airfield (30% risk threshold).

GFS currently has the highest 48 hour totals over parts of northern England,
more especially over the Pennineshttp://91.121.93.17/pics/Rmgfs48sum.gif

Visible imagery has some deeper looking tops due west of Biscayhttp://www.metoffice.gov.uk/satpics/latest_VIS.html

Jon.

Finally got a weather warning! I've been convinced for a day that this
wave depression would produce some very heavy rain, but pinpointing it
was beyond me! It has ended up further North than it looked like it
would get, but there has been some excellent convection in
instability, in advance of the front, creating storms for some. Then,
as the wave tracked NE, another area of deep convection has brought
thunderstorms and heavy rain to the North Midlands and Yorkshire. The
present weather radar shows that heavy rain now in in the NE of
England/ SE of Scotland and there's another nice circulation producing
some heavy rain over Wales too. That could drag some storms over the
SW later - perhaps they are just beginning to show in the SW
approaches.

An interesting night to come for some! Many of us, however, may be
left thinking what all the fuss has been about!

Paul

On Apr 27, 10:47*pm, Dawlish wrote:
On Apr 26, 12:56*pm, "Jon O'Rourke" wrote:





"Dawlish" wrote in message

...

The Met Office still don't think the rain will be heavy enough for any
kind of advisory/warning tomorrow. The FAX charts still show the

development of that wave depression and I still think there could be

some atmospheric fireworks in some areas and some very heavy rain with
that set-up.

Some heavy rain is likely but the detail has varied a bit from run to run
and hence the risk for any particular area is probably deemed less than the
required 40%http://www.metoffice.gov.uk/weather/...warnings..html
To a certain extent this is reflected in the 1000Z issue Long TAFs which
indicate moderate rain with no mention of heavy as yet for any particular
airfield (30% risk threshold).

GFS currently has the highest 48 hour totals over parts of northern England,
more especially over the Pennineshttp://91.121.93.17/pics/Rmgfs48sum.gif

Visible imagery has some deeper looking tops due west of Biscayhttp://www.metoffice.gov.uk/satpics/latest_VIS.html

Jon.

Finally got a weather warning! I've been convinced for a day that this
wave depression would produce some very heavy rain, but pinpointing it
was beyond me! It has ended up further North than it looked like it
would get, but there has been some excellent convection in
instability, in advance of the front, creating storms for some. Then,
as the wave tracked NE, another area of deep convection has brought
thunderstorms and heavy rain to the North Midlands and Yorkshire. The
present weather radar shows that heavy rain now in in the NE of
England/ SE of Scotland and there's another nice circulation producing
some heavy rain over Wales too. That could drag some storms over the
SW later - perhaps they are just beginning to show in the SW
approaches.

An interesting night to come for some! Many of us, however, may be
left thinking what all the fuss has been about!

Paul- Hide quoted text -

- Show quoted text -

HI all,

Monday - Another fascinating day weatherwise. That little wave has
begun to occlude, but is still being accompanied by some very heavy
rainfall in Fife and Perthshire. It's slow-moving too. There could
well be reports of flooding with that lot.

It shows that the uplift associated with this wave depression and the
location of the heaviest precipitation at a given future point was
extremely hard for the MO to predict. No weather warnings were given
up until late on Sunday afternoon, as far as I'm aware and I can fully
understand why. I was expecting the major area of uplift to be to the
SE of the main trough and there were some significant trough lines and
some thunderstorms, but they were concentrated in bands and many areas
missed out and stayed dry.

For the main trough and its developing wave to drift so far North,
took forecasters by surprise; as did the intensity of the
precipitation that developed around the centre of the developing low.
So: not a great forecast, MO, late on the weather warning, but
entirely understandable. Its possibly down to data grid sizes and the
small area occupied by the "wet" part of that wave. The forecast
models just didn't have enough data to produce accurate forecasts of
precipitation intensity and location.

Dead interesting though - as was that circulation over Wales last
night and the rain which is presently over NW England, behind the main
trough. It looks like an eddy effect, swirling behind the first wave,
or it may be that the wave developed a double centre and the second on
is beginning to decay and is being presently re-absorbed. Any other
views on all this?

Paul

"Dawlish" wrote in message
...

For the main trough and its developing wave to drift so far North,
took forecasters by surprise; as did the intensity of the
precipitation that developed around the centre of the developing low.

So: not a great forecast, MO, late on the weather warning, but
entirely understandable. Its possibly down to data grid sizes and the
small area occupied by the "wet" part of that wave. The forecast
models just didn't have enough data to produce accurate forecasts of
precipitation intensity and location.

I don't think that's how or why it happened. The main frontal zone was split
with elevated storms tied to the forward upper front, effectively in the
warm sector, with further storms developing to the rear of this in and
around the shallow moist zone/near the surface front. Hence the wave, as far
as I can tell, wasn't the key player that it was originally expected to be
and didn't really develop over the UK. Also, given that much of the forward
precip. was falling into a relatively dry boundary layer surface totals were
likely to be low and not necessarily likely to trigger flash warnings.
Either way all the models that I'd seen struggled with the complexity of it
all and it looked like a very difficult day for those tasked with getting
the detail right.

00Z ASXX http://www.wetterzentrale.de/archive...ka20080428.gif
showing the split system.

Jon.

On Apr 28, 12:20*pm, "Jon O'Rourke" wrote:
"Dawlish" wrote in message

...

For the main trough and its developing wave to drift so far North,
took forecasters by surprise; as did the intensity of the
precipitation that developed around the centre of the developing low.
So: not a great forecast, MO, late on the weather warning, but
entirely understandable. Its possibly down to data grid sizes and the
small area occupied by the "wet" part of that wave. The forecast
models just didn't have enough data to produce accurate forecasts of
precipitation intensity and location.

I don't think that's how or why it happened. The main frontal zone was split
with elevated storms tied to the forward upper front, effectively in the
warm sector, with further storms developing to the rear of this in and
around the shallow moist zone/near the surface front. Hence the wave, as far
as I can tell, wasn't the key player that it was originally expected to be
and didn't really develop over the UK. Also, given that much of the forward
precip. was falling into a relatively dry boundary layer surface totals were
likely to be low and not necessarily likely to trigger flash warnings.
Either way all the models that I'd seen struggled with the complexity of it
all and it looked like a very difficult day for those tasked with getting
the detail right.

00Z ASXXhttp://www.wetterzentrale.de/archive/2008/brack/bracka20080428.gif
showing the split system.

Jon.

I agree, Jon. It certainly wasn't easy! I'm not sure why you say that
the wave didn't develop over the UK. Did you mean "England" It
certainly developed over the UK, though not so much over central
England, as was forecast Friday/Saturday. Instead it developed over
the far NE of England and finally gave some high rainfall totals over
SE Scotland, triggering the eventual weather warning. It ran along the
trough, pressure fell as it did so and a clear circulation developed,
with a warm sector, which is shown to be occluding on the present FAX
chart. Thank you for your analysis of the front over England though.
Yes, there were clear pre frontal troughs, consistent with the front
splitting, producing pre-frontal instability and the air was dry. In
England, high rainfall totals only occurred along these lines of
destabilisation and even then were not enough, as you say, to have
triggered a weather warning. I've read reports of rain being seen at a
distance, but very little being recorded at ground level. A lot of
evaporation may have occurred in the precipitation from some of those
lines of showers.

Much of England, Southern Scotland, Wales and Ireland appears to have
chicken pox today with some beefy showers, one of which is presently
falling on Dawlish!

With the stalled Atlantic I talked about, we're likely to have the
unusual circumstance of a retrogressing low. It looks like it will
move W to E, bringing us into the coold Northerlies that I'd forecast
for the 1st May, but that now looks unlikely, with it heading into the
Atlantic and allowing some warm air to spread across the UK for next
weekend. Another possible, plume, 21C+, possible thundery breakdown
and showers/bands of rain/strong sunshine in-between, all this week
too! Suprb weather watching!

Off out over the Haldon Hills soon, on my way to the gym. Looking
forward to seeing some big Cu+/Cbs. I'll wave at Haytor from little
Haldon, Will!

Paul

"Dawlish" wrote in message
...

I agree, Jon. It certainly wasn't easy! I'm not sure why you say that
the wave didn't develop over the UK. Did you mean "England" It
certainly developed over the UK, though not so much over central
England, as was forecast Friday/Saturday.

Yes, essentially England and Wales. I haven't looked at the totals but I
only noticed one flash warning for NE England yesterday evening and if
anything that looked to be linked to the activity on the surface cold front
rather than the wave/developing occlusion.

Jon.

On Apr 28, 2:43*pm, "Jon O'Rourke" wrote:
"Dawlish" wrote in message

...

I agree, Jon. It certainly wasn't easy! I'm not sure why you say that
the wave didn't develop over the UK. Did you mean "England" It
certainly developed over the UK, though not so much over central
England, as was forecast Friday/Saturday.

Yes, essentially England and Wales. I haven't looked at the totals but I
only noticed one flash warning for NE England yesterday evening and if
anything that looked to be linked to the activity on the surface cold front
rather than the wave/developing occlusion.

Jon.

Yes, could be. Thanks for your help.

Paul

On Apr 25, 7:54*pm, Dawlish wrote:
Possible May
Easterlies for the UK? Paul Simons writes about exactly that in The
Tombs today and talked about the NW of Scotland sometimes having the
best of the UK weather at this time of year, if the Atlantic does
completely stall, allowing Easterlies to develop.

Paul

Looking possible with developments over the alst couple of days on the
gfs.

http://www.wetterzentrale.de/pics/Rtavn2402.png at T+240 and

http://www.wetterzentrale.de/pics/Rtavn2762.png at T+276

Some opportunities for some warmth, next weekend before that though. A
warm and a dry Bank Holiday?

Paul