In message , Len
writes
On Thursday, July 26, 2018 at 8:24:32 PM UTC+1, John Hall wrote:

The thing I notice most is how different the temperatures in those
hourly computer-generated forecasts are from the maxima and minima
included as part of the textual human-generated forecasts. In hot summer
weather, such as we are having now, the computer-generated temperatures
seem to be substantially lower. In cold winter weather they seem to be
higher. The human-generated figures normally seem to be far closer to
reality.

I notice the same down here on the SW Devon coast John.
The max for the last few days has been forecast for the next day as
21C. It has reached 24 or 25C each day. I wonder if the models are
trying to factor in a sea breeze. I don't think they are that clever,
evidently not that clever with the temperature.

I don't think that would be a factor here. I live thirty miles from the
nearest coast, and it would be unusual for a sea breeze to penetrate
this far, especially as the South Downs would be in the way.
--
John Hall
"Hegel was right when he said that we learn from history
that man can never learn anything from history."
George Bernard Shaw (1856-1950)

John Hall wrote:

In message ,
Len writes
On Thursday, July 26, 2018 at 8:24:32 PM UTC+1, John Hall wrote:

The thing I notice most is how different the temperatures in those
hourly computer-generated forecasts are from the maxima and minima
included as part of the textual human-generated forecasts. In hot
summer weather, such as we are having now, the computer-generated
temperatures seem to be substantially lower. In cold winter
weather they seem to be higher. The human-generated figures
normally seem to be far closer to reality.

I notice the same down here on the SW Devon coast John.
The max for the last few days has been forecast for the next day as
21C. It has reached 24 or 25C each day. I wonder if the models are
trying to factor in a sea breeze. I don't think they are that
clever, evidently not that clever with the temperature.

I don't think that would be a factor here. I live thirty miles from
the nearest coast, and it would be unusual for a sea breeze to
penetrate this far, especially as the South Downs would be in the way.

It's surprising how far a sea breeze will penetrate in the right
conditions. In Tideswell we occasionally get a sea breeze from
Liverpool Bay and that's over 50 miles away.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
Twitter: @TideswellWeathr

Another curiosity I've just noticed for this afternoon is a predicted
rainfall probability comparison for Ely and Cambridge (just 15 miles
apart, both of course well inland) and both on the 1200 forecast

Time Ely Cambridge

1500 10% 50%
1600 50% 5%
1700 50% 5%
1800 50% 5%
1900 60% 60%
2000 60% 30%
2100 60% 10%
2200 70% 10%
2300 20% 10%

(Sorry don't know how well the formatting will hold up!)

I guess the storms will be coming broadly from the S/SW and travelling
at eg 10mph so Cambridge might be one hour ahead of Ely for a given
storm cell. NB Cambridge is approx 15 miles SSE of Ely.

But it's odd - apparently high resolution predictions but not too much
correlation between two places that are quite close neighbours.

On Friday, 27 July 2018 13:31:28 UTC+1, JGD wrote:
Another curiosity I've just noticed for this afternoon is a predicted
rainfall probability comparison for Ely and Cambridge (just 15 miles
apart, both of course well inland) and both on the 1200 forecast

Time Ely Cambridge

1500 10% 50%
1600 50% 5%
1700 50% 5%
1800 50% 5%
1900 60% 60%
2000 60% 30%
2100 60% 10%
2200 70% 10%
2300 20% 10%

(Sorry don't know how well the formatting will hold up!)

I guess the storms will be coming broadly from the S/SW and travelling
at eg 10mph so Cambridge might be one hour ahead of Ely for a given
storm cell. NB Cambridge is approx 15 miles SSE of Ely.

But it's odd - apparently high resolution predictions but not too much
correlation between two places that are quite close neighbours.
Looking at the latest observations in that area, there appears to be a lot of convergence going on north of Cambridge, so the model may not be too far out. There will be around 15 model grid points between Camridge and Ely, so it should be able to capture the small scale of the convergence. Obviously if there is a positional error then the weather type at a given location will be completely different!

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (no wind measurement currently)

JGD wrote:

Another curiosity I've just noticed for this afternoon is a predicted
rainfall probability comparison for Ely and Cambridge (just 15 miles
apart, both of course well inland) and both on the 1200 forecast

Time Ely Cambridge

1500 10% 50%
1600 50% 5%
1700 50% 5%
1800 50% 5%
1900 60% 60%
2000 60% 30%
2100 60% 10%
2200 70% 10%
2300 20% 10%

(Sorry don't know how well the formatting will hold up!)

I guess the storms will be coming broadly from the S/SW and
travelling at eg 10mph so Cambridge might be one hour ahead of Ely
for a given storm cell. NB Cambridge is approx 15 miles SSE of Ely.

But it's odd - apparently high resolution predictions but not too
much correlation between two places that are quite close neighbours.


This morning I had reason to look at the wind forecasts for Anglesey
for tomorrow. For the period between 0900z and 1200z the Met office
website is predicting SW Force 5 for Valley whereas the BBC website is
predicting SSW Force 8, also for Valley. You pays your money and you
takes your choice. These forecasts are, of course, fully automated and
I suppose they are based on different models. The perils of issuing raw
model ouput as end-user material. I can't see any justification for
doing so.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
Twitter: @TideswellWeathr

On 27/07/2018 13:31, JGD wrote:
NB Cambridge is approx 15 miles SSE of Ely.


Before someone picks me up on it, I meant SSW of course.

I don't have the patience to monitor this for long, but the 1300
forecast (ie just one hour after the previous post) shows

Time Ely 1200 Ely 1300 Forecast
1500 10% 10%
1600 50% 50%
1700 50% 30%
1800 50% 30%
1900 60% 60%
2000 60% 40%
2100 60% 40%
2200 70% 70%
2300 10% 40%

Still broadly the same pattern of course but significant differences now
just 4-5 hours out. Warning has changed from yellow to amber.

The solution clearly is evolving quite speedily hour to hour. Apologies
if this is very familiar to some here, but I've only just noticed the
variability of the short-term forecasting trends.


On 27/07/2018 13:31, JGD wrote:
Another curiosity I've just noticed for this afternoon is a predicted
rainfall probability comparison for Ely and Cambridge (just 15 miles
apart, both of course well inland) and both on the 1200 forecast

TimeÂ*Â*Â*Â* ElyÂ*Â*Â*Â* Cambridge

1500Â*Â*Â*Â* 10%Â*Â*Â*Â* 50%
1600Â*Â*Â*Â* 50%Â*Â*Â*Â* 5%
1700Â*Â*Â*Â* 50%Â*Â*Â*Â* 5%
1800Â*Â*Â*Â* 50%Â*Â*Â*Â* 5%
1900Â*Â*Â*Â* 60%Â*Â*Â*Â* 60%
2000Â*Â*Â*Â* 60%Â*Â*Â*Â* 30%
2100Â*Â*Â*Â* 60%Â*Â*Â*Â* 10%
2200Â*Â*Â*Â* 70%Â*Â*Â*Â* 10%
2300Â*Â*Â*Â* 20%Â*Â*Â*Â* 10%

(Sorry don't know how well the formatting will hold up!)

I guess the storms will be coming broadly from the S/SW and travelling
at eg 10mph so Cambridge might be one hour ahead of Ely for a given
storm cell. NB Cambridge is approx 15 miles SSE of Ely.

But it's odd - apparently high resolution predictions but not too much
correlation between two places that are quite close neighbours.

On Friday, 27 July 2018 13:58:31 UTC+1, Norman Lynagh wrote:
JGD wrote:
This morning I had reason to look at the wind forecasts for Anglesey
for tomorrow. For the period between 0900z and 1200z the Met office
website is predicting SW Force 5 for Valley whereas the BBC website is
predicting SSW Force 8, also for Valley. You pays your money and you
takes your choice. These forecasts are, of course, fully automated and
I suppose they are based on different models.
There is a trough rotating north-eastwards across that area. The Met Office model has it clearing north of Valley between 0600z and 0700z, with strong SSWly winds ahead and less strong (but still lively) SWly winds behind. Looks as if the Met Office model is quicker with this than whatever model the BBC is using today.

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (no wind measurement currently)

Freddie wrote:

On Friday, 27 July 2018 13:58:31 UTC+1, Norman Lynagh wrote:
JGD wrote:
This morning I had reason to look at the wind forecasts for Anglesey
for tomorrow. For the period between 0900z and 1200z the Met office
website is predicting SW Force 5 for Valley whereas the BBC website
is predicting SSW Force 8, also for Valley. You pays your money and
you takes your choice. These forecasts are, of course, fully
automated and I suppose they are based on different models.
There is a trough rotating north-eastwards across that area. The Met
Office model has it clearing north of Valley between 0600z and 0700z,
with strong SSWly winds ahead and less strong (but still lively) SWly
winds behind. Looks as if the Met Office model is quicker with this
than whatever model the BBC is using today.


It does highlight what a nonsense it is to attempt categoric
location/time specific forecasting. Even at 24 hours out there is
always a degree of uncertainty. An expression of this uncertainty
should be an integral part of any forecast. I'll get off my soapbox now
:-)

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
https://peakdistrictweather.org
Twitter: @TideswellWeathr

On Friday, 27 July 2018 15:10:12 UTC+1, Norman Lynagh wrote:
Freddie wrote:

On Friday, 27 July 2018 13:58:31 UTC+1, Norman Lynagh wrote:
JGD wrote:
This morning I had reason to look at the wind forecasts for Anglesey
for tomorrow. For the period between 0900z and 1200z the Met office
website is predicting SW Force 5 for Valley whereas the BBC website
is predicting SSW Force 8, also for Valley. You pays your money and
you takes your choice. These forecasts are, of course, fully
automated and I suppose they are based on different models.
There is a trough rotating north-eastwards across that area. The Met
Office model has it clearing north of Valley between 0600z and 0700z,
with strong SSWly winds ahead and less strong (but still lively) SWly
winds behind. Looks as if the Met Office model is quicker with this
than whatever model the BBC is using today.


It does highlight what a nonsense it is to attempt categoric
location/time specific forecasting. Even at 24 hours out there is
always a degree of uncertainty. An expression of this uncertainty
should be an integral part of any forecast.
Indeed! But folk love their deterministic forecasts :-)

I'll get off my soapbox now
:-)
:-)

--
Freddie
Ystrad
Rhondda
148m AMSL
http://www.hosiene.co.uk/weather/
https://twitter.com/YstradRhonddaWx for hourly reports (no wind measurement currently)