Only last night they were predicting heavy rain for kent this morning and
moderate rain for London and the rest of the SE. Actual weather? Nothing of
the sort. A few scattered patches of drizzle with the main rain band way off in
Belgium. How can they get it so wrong only 12 hours in advance? Did the wind
suddenly turn 90 degrees overnight?

--
Spud

On Wednesday, 30 August 2017 09:29:47 UTC+1, wrote:
Only last night they were predicting heavy rain for kent this morning and
moderate rain for London and the rest of the SE. Actual weather? Nothing of
the sort. A few scattered patches of drizzle with the main rain band way off in
Belgium. How can they get it so wrong only 12 hours in advance? Did the wind
suddenly turn 90 degrees overnight?
Nothing to do with the wind direction (as you present it) and everything to do with the way small variations in shape and speed within the jet interact with the moisture in the lower and middle troposphere. Tiny errors in analysis have a massive impact on the end result - and the impacts change dramatically in a very short period of time. The forecasters know their stuff, it's just they sometimes can't keep up with the changes.

Never forget that the atmosphere is a complex three-dimensional beast that would be almost totally unpredictable without computer models.

Having said all that, I agree that it was a poor forecast. The only way handling of these situations can improve is through better modelling (more horizontal and vertical resolution, and more responsive assimilation of current data) which will enable a better response to when the forecast looks like going adrift.

On Wed, 30 Aug 2017 02:51:00 -0700 (PDT)
Freddie wrote:

On Wednesday, 30 August 2017 09:29:47 UTC+1, wrote:
Only last night they were predicting heavy rain for kent this morning and
moderate rain for London and the rest of the SE. Actual weather? Nothing of
the sort. A few scattered patches of drizzle with the main rain band way
off in Belgium. How can they get it so wrong only 12 hours in advance? Did
the wind suddenly turn 90 degrees overnight?
Nothing to do with the wind direction (as you present it) and everything to
do with the way small variations in shape and speed within the jet interact
with the moisture in the lower and middle troposphere. Tiny errors in
analysis have a massive impact on the end result - and the impacts change
dramatically in a very short period of time. The forecasters know their
stuff, it's just they sometimes can't keep up with the changes.

Never forget that the atmosphere is a complex three-dimensional beast that
would be almost totally unpredictable without computer models.

Having said all that, I agree that it was a poor forecast. The only way
handling of these situations can improve is through better modelling (more
horizontal and vertical resolution, and more responsive assimilation of
current data) which will enable a better response to when the forecast looks
like going adrift.


Better communication of uncertainties would help too.

Will
--



---
This email has been checked for viruses by AVG.
http://www.avg.com

On Wednesday, 30 August 2017 10:55:15 UTC+1, wrote:
On Wed, 30 Aug 2017 02:51:00 -0700 (PDT)
Freddie wrote:

On Wednesday, 30 August 2017 09:29:47 UTC+1, wrote:
Only last night they were predicting heavy rain for kent this morning and
moderate rain for London and the rest of the SE. Actual weather? Nothing of
the sort. A few scattered patches of drizzle with the main rain band way
off in Belgium. How can they get it so wrong only 12 hours in advance? Did
the wind suddenly turn 90 degrees overnight?
Nothing to do with the wind direction (as you present it) and everything to
do with the way small variations in shape and speed within the jet interact
with the moisture in the lower and middle troposphere. Tiny errors in
analysis have a massive impact on the end result - and the impacts change
dramatically in a very short period of time. The forecasters know their
stuff, it's just they sometimes can't keep up with the changes.

Never forget that the atmosphere is a complex three-dimensional beast that
would be almost totally unpredictable without computer models.

Having said all that, I agree that it was a poor forecast. The only way
handling of these situations can improve is through better modelling (more
horizontal and vertical resolution, and more responsive assimilation of
current data) which will enable a better response to when the forecast looks
like going adrift.


Better communication of uncertainties would help too.

Very true - but if the models aren't showing much in the way of uncertainty (i.e. it is implied by past experience rather than model output) then what would/could you say with any authority - especially as experience has become very diluted over time....

--
Freddie
Fishpool Farm
Hyssington
Powys
296m AMSL
http://www.fishpoolfarmweather.co.uk/
https://twitter.com/FishpoolFarmWx for hourly reports

I usually don't rise to this kind of message (I usually post on another newsgroup) but today I will. Spud, I saw your message first earlier this morning - at that time I nearly replied with two words - 'look west'. You clearly checked the radar imagery and correctly saw the showers to the east of London. Just as forecast yesterday. To the west, the reactivated front was already spreading rain east across southern England. As forecast yesterday. Careful viewing of yesterday's forecasts would have revealed that the rain in the SE was basically going to come from the front moving east rather than from the showers.

Here in north Surrey it has rained for the last 4 hours, quite heavily in the last hour. It is soon to clear. You do not reveal where you live.

Freddie, I am surprised that you agree that it was a poor forecast. Maybe you have other reasons to say this.

On a final note, I think the various forecast models did a great job handling today's abrupt change in weather / synoptic type, especially as it is a rather unusual transition. I highlighted today's situation back on Saturday when I was forecasting (not for the Met Office) - I recall that they were projecting two pptn areas converging - just as they have actually done. I think that's pretty impressive. I agree with Will that communication of uncertainty is important and any clients who received forecasts from me last weekend got a hefty dose of uncertainty about today and tomorrow.

Today is certainly worthy of comment but for the abrupt change in synoptic type and of temperature in the SE.

Regards Julian
Julian Mayes
Surrey
In the rain.

On Wed, 30 Aug 2017 05:56:05 -0700 (PDT)
wrote:
I usually don't rise to this kind of message (I usually post on another new=
sgroup) but today I will. Spud, I saw your message first earlier this morni=
ng - at that time I nearly replied with two words - 'look west'. You clearl=
y checked the radar imagery and correctly saw the showers to the east of Lo=
ndon. Just as forecast yesterday. To the west, the reactivated front was a=
lready spreading rain east across southern England. As forecast yesterday. =
Careful viewing of yesterday's forecasts would have revealed that the rain=
in the SE was basically going to come from the front moving east rather th=
an from the showers.=20

Yes, but it didn't. See below.

Here in north Surrey it has rained for the last 4 hours, quite heavily in t=
he last hour. It is soon to clear. You do not reveal where you live.=20

London area. Yes, its raining now, but instead of a band of rain that came
in from france - which actually looked like it headed off to belgium instead -
on the rain radar it looks like the band of rain from the west which was
predicted to fade away instead intensified.

--
Spud

On Wed, 30 Aug 2017 13:40:00 +0000 (UTC)
d wrote:

On Wed, 30 Aug 2017 05:56:05 -0700 (PDT)
wrote:
I usually don't rise to this kind of message (I usually post on another new=
sgroup) but today I will. Spud, I saw your message first earlier this morni=
ng - at that time I nearly replied with two words - 'look west'. You clearl=
y checked the radar imagery and correctly saw the showers to the east of Lo=
ndon. Just as forecast yesterday. To the west, the reactivated front was a=
lready spreading rain east across southern England. As forecast yesterday. =
Careful viewing of yesterday's forecasts would have revealed that the rain=
in the SE was basically going to come from the front moving east rather th=
an from the showers.=20

Yes, but it didn't. See below.

Here in north Surrey it has rained for the last 4 hours, quite heavily in t=
he last hour. It is soon to clear. You do not reveal where you live.=20

London area. Yes, its raining now, but instead of a band of rain that came
in from france - which actually looked like it headed off to belgium instead -
on the rain radar it looks like the band of rain from the west which was
predicted to fade away instead intensified.


Sorry but that is simply not true. The MetO TV forecasts clearly indicated rain
coming in from the west today and persisting in the far SE. IIRC it was also
mentioned that some of the rain could be heavy.

Will (Haytor, Devon, 1017 feet asl)
--

---
This email has been checked for viruses by AVG.
http://www.avg.com

On Wed, 30 Aug 2017 15:57:58 +0100
Will Hand wrote:
On Wed, 30 Aug 2017 13:40:00 +0000 (UTC)
wrote:

On Wed, 30 Aug 2017 05:56:05 -0700 (PDT)
wrote:
I usually don't rise to this kind of message (I usually post on another new=
sgroup) but today I will. Spud, I saw your message first earlier this morni=
ng - at that time I nearly replied with two words - 'look west'. You clearl=
y checked the radar imagery and correctly saw the showers to the east of Lo=
ndon. Just as forecast yesterday. To the west, the reactivated front was a=
lready spreading rain east across southern England. As forecast yesterday. =
Careful viewing of yesterday's forecasts would have revealed that the rain=
in the SE was basically going to come from the front moving east rather th=
an from the showers.=20

Yes, but it didn't. See below.

Here in north Surrey it has rained for the last 4 hours, quite heavily in t=
he last hour. It is soon to clear. You do not reveal where you live.=20

London area. Yes, its raining now, but instead of a band of rain that came
in from france - which actually looked like it headed off to belgium instead
-
on the rain radar it looks like the band of rain from the west which was
predicted to fade away instead intensified.


Sorry but that is simply not true. The MetO TV forecasts clearly indicated rain
coming in from the west today and persisting in the far SE. IIRC it was also

Not the one I saw yesterday. The rain over the SE was clearly a front that
was going to come in from France and the front in the east of england would
fade.

--
Spud

On Wed, 30 Aug 2017 15:13:01 +0000 (UTC)
d wrote:

On Wed, 30 Aug 2017 15:57:58 +0100
Will Hand wrote:
On Wed, 30 Aug 2017 13:40:00 +0000 (UTC)
wrote:

On Wed, 30 Aug 2017 05:56:05 -0700 (PDT)
wrote:
I usually don't rise to this kind of message (I usually post on another
new= sgroup) but today I will. Spud, I saw your message first earlier
this morni= ng - at that time I nearly replied with two words - 'look
west'. You clearl= y checked the radar imagery and correctly saw the
showers to the east of Lo= ndon. Just as forecast yesterday. To the
west, the reactivated front was a= lready spreading rain east across
southern England. As forecast yesterday. =
Careful viewing of yesterday's forecasts would have revealed that the
rain= in the SE was basically going to come from the front moving east
rather th=
an from the showers.=20

Yes, but it didn't. See below.

Here in north Surrey it has rained for the last 4 hours, quite heavily in
t= he last hour. It is soon to clear. You do not reveal where you
live.=20

London area. Yes, its raining now, but instead of a band of rain that came
in from france - which actually looked like it headed off to belgium
instead
-
on the rain radar it looks like the band of rain from the west which was
predicted to fade away instead intensified.


Sorry but that is simply not true. The MetO TV forecasts clearly indicated
rain coming in from the west today and persisting in the far SE. IIRC it was
also

Not the one I saw yesterday. The rain over the SE was clearly a front that
was going to come in from France and the front in the east of england would
fade.


OK fair enough. I didn't see all the forecasts.



---
This email has been checked for viruses by AVG.
http://www.avg.com

On Wednesday, 30 August 2017 13:56:06 UTC+1, wrote:

Freddie, I am surprised that you agree that it was a poor forecast. Maybe you have other reasons to say this.

Julian, I took Spud's transcription of the forecast for the morning at face value - I didn't actually see the forecast itself. I was focussing on what may go wrong with a forecast of an upper trough causing development of either the western polar front or the eastern elevated moist air. I apologise if I caused offence.

--
Freddie
Fishpool Farm
Hyssington
Powys
296m AMSL
http://www.fishpoolfarmweather.co.uk/
https://twitter.com/FishpoolFarmWx for hourly reports