In just a couple of hours, the rain band has developed from something
pretty light and fragmented into a far larger and intense area of rain.
What makes this happen so quickly, it was certainly well forecast.
--
Col

Bolton, Lancashire
160m asl

On 16/07/2011 08:57, Col wrote:
In just a couple of hours, the rain band has developed from something
pretty light and fragmented into a far larger and intense area of rain.
What makes this happen so quickly, it was certainly well forecast.

Col,

There is an explanation on:

http://www.ukweatherworld.co.uk/

I cannot claim to understand it all!
--
Phil
Guildford

On Jul 16, 8:57*am, "Col" wrote:
In just a couple of hours, the rain band has developed from something
pretty light and fragmented into a far larger and intense area of rain.
What makes this happen so quickly, it was certainly well forecast.
--
Col

Bolton, Lancashire
160m asl

Presumably it is due to the air rising as it passes over land. In
other words it it is the vertical movement not the related horizontal
movement.

Cheers, Alastair.

On 16/07/2011 09:30, Phil Layton wrote:
On 16/07/2011 08:57, Col wrote:
In just a couple of hours, the rain band has developed from something
pretty light and fragmented into a far larger and intense area of rain.
What makes this happen so quickly, it was certainly well forecast.

Col,

There is an explanation on:

http://www.ukweatherworld.co.uk/

I cannot claim to understand it all!

The gist of it is that a disturbance in the upper troposphere (which is
where the 300mb level is) is interacting with the system below it. It
is interacting in such a way that the air in the lower to middle
atmosphere is being forced upwards. As this air is relatively warm and
moist, this forced ascent will produce plenty of condensation and hence
rain.

Upper troughs are normally associated with cold air aloft and so this
running over the warm "tongue" between the warm and cold fronts below
will destablise the atmosphere. This adds a convective element to the
rain, and it has been noticeable here in Ashurst that there has not been
continuous moderate or heavy rain but bursts (sometimes only a minute or
two long) of heavier rain embedded in generally light precipitation.

Someone else has mentioned the air being forced to rise as it reaches
the land, but this effect is taking place at a much lower level in the
atmosphere and is also more localised. This will produce areas of
persistent heavier rain on windward coasts and hills but will have much
less effect generally.

Someone can doubtless come along with a more technically rigorous
explanation, but I have tried to keep it as simple as I can.

--
- Yokel -

Yokel posts via a spam-trap account which is not read.

On 16/07/2011 12:03, Yokel wrote:


The gist of it is that a disturbance in the upper troposphere (which is
where the 300mb level is) is interacting with the system below it. It is
interacting in such a way that the air in the lower to middle atmosphere
is being forced upwards. As this air is relatively warm and moist, this
forced ascent will produce plenty of condensation and hence rain.

Upper troughs are normally associated with cold air aloft and so this
running over the warm "tongue" between the warm and cold fronts below
will destablise the atmosphere. This adds a convective element to the
rain, and it has been noticeable here in Ashurst that there has not been
continuous moderate or heavy rain but bursts (sometimes only a minute or
two long) of heavier rain embedded in generally light precipitation.

Someone else has mentioned the air being forced to rise as it reaches
the land, but this effect is taking place at a much lower level in the
atmosphere and is also more localised. This will produce areas of
persistent heavier rain on windward coasts and hills but will have much
less effect generally.

Someone can doubtless come along with a more technically rigorous
explanation, but I have tried to keep it as simple as I can.


Thanks Yokel. I sometimes think that a '3D' type chart may explain this
better than just looking at a normal synoptic chart with fronts.

--
Phil
Guildford

Yokel wrote:
On 16/07/2011 09:30, Phil Layton wrote:
On 16/07/2011 08:57, Col wrote:
In just a couple of hours, the rain band has developed from
something pretty light and fragmented into a far larger and intense
area of rain. What makes this happen so quickly, it was certainly
well forecast.

Col,

There is an explanation on:

http://www.ukweatherworld.co.uk/

I cannot claim to understand it all!

The gist of it is that a disturbance in the upper troposphere (which
is where the 300mb level is) is interacting with the system below it.
It is interacting in such a way that the air in the lower to middle
atmosphere is being forced upwards. As this air is relatively warm and
moist, this forced ascent will produce plenty of condensation and
hence rain.

Upper troughs are normally associated with cold air aloft and so this
running over the warm "tongue" between the warm and cold fronts below
will destablise the atmosphere. This adds a convective element to the
rain, and it has been noticeable here in Ashurst that there has not
been continuous moderate or heavy rain but bursts (sometimes only a
minute or two long) of heavier rain embedded in generally light
precipitation.

Yes, I noticed exactly the same thing here when I was in the main
rain band. Generally moderate rain but every so often it would
suddenly intensify to heavy rain for just a few minutes.

Someone else has mentioned the air being forced to rise as it reaches
the land, but this effect is taking place at a much lower level in the
atmosphere and is also more localised. This will produce areas of
persistent heavier rain on windward coasts and hills but will have
much less effect generally.

Someone can doubtless come along with a more technically rigorous
explanation, but I have tried to keep it as simple as I can.

No, that's a good exlanation, it's right at my level
--
Col

Bolton, Lancashire
160m asl

On Jul 16, 12:19*pm, "Col" wrote:
Yokel wrote:
On 16/07/2011 09:30, Phil Layton wrote:
On 16/07/2011 08:57, Col wrote:
In just a couple of hours, the rain band has developed from
something pretty light and fragmented into a far larger and intense
area of rain. What makes this happen so quickly, it was certainly
well forecast.

Col,

There is an explanation on:

http://www.ukweatherworld.co.uk/

I cannot claim to understand it all!

The gist of it is that a disturbance in the upper troposphere (which
is where the 300mb level is) is interacting with the system below it.
It is interacting in such a way that the air in the lower to middle
atmosphere is being forced upwards. As this air is relatively warm and
moist, this forced ascent will produce plenty of condensation and
hence rain.

Upper troughs are normally associated with cold air aloft and so this
running over the warm "tongue" between the warm and cold fronts below
will destablise the atmosphere. *This adds a convective element to the
rain, and it has been noticeable here in Ashurst that there has not
been continuous moderate or heavy rain but bursts (sometimes only a
minute or two long) of heavier rain embedded in generally light
precipitation.

Yes, I noticed exactly the same thing here when I was in the main
rain band. Generally moderate rain but every so often it would
suddenly intensify to heavy rain for just a few minutes.

Someone else has mentioned the air being forced to rise as it reaches
the land, but this effect is taking place at a much lower level in the
atmosphere and is also more localised. *This will produce areas of
persistent heavier rain on windward coasts and hills but will have
much less effect generally.

Someone can doubtless come along with a more technically rigorous
explanation, but I have tried to keep it as simple as I can.

No, that's a good exlanation, it's right at my level
--
Col

Bolton, Lancashire
160m asl- Hide quoted text -

- Show quoted text -

Wish it had intensified here! We've had well under a millimeter of
rain from this and nothing has gone into my water butts!! For us it's
been a pretty dreadful forecast.

On Sat, 16 Jul 2011 at 08:57:06, Col wrote
in uk.sci.weather :

In just a couple of hours, the rain band has developed from something
pretty light and fragmented into a far larger and intense area of rain.

Yes, when I looked at Raintoday at 6.30 this morning, there looked to be
very little to it - but two hours later it was ****ing down!
--
Paul Hyett, Cheltenham (change 'invalid83261' to 'blueyonder' to email me)