Inconsistent forecasts

[jac]

Just looking at the forecast for tomorrow.

Windguru (GFS) showing very light winds 3-4 knots , light cloud no precipitation.
Coastal Forecast for Solent and Christchurch bay showing winds up to force 4 with F6 gusts, heavy rain and heavy rain showers

Then look at the BBC land forecasts for areas such as Yarmouth, Bembridge, Hamble and seems to reinforce the Windguru model i.e. 5mph winds, no precipitation, light cloud.

Given that the shipping forecast and the BBC land forecasts are both Met Office it seems odd that they would end up so different.

 

[matt1]

Just looking at the forecast for tomorrow.

Windguru (GFS) showing very light winds 3-4 knots , light cloud no precipitation.
Coastal Forecast for Solent and Christchurch bay showing winds up to force 4 with F6 gusts, heavy rain and heavy rain showers

Then look at the BBC land forecasts for areas such as Yarmouth, Bembridge, Hamble and seems to reinforce the Windguru model i.e. 5mph winds, no precipitation, light cloud.

Given that the shipping forecast and the BBC land forecasts are both Met Office it seems odd that they would end up so different.

I'm losing confidence in the met office. Perhaps because of their (in my view) ridiculous over use of weather warnings, I've become somewhat cynical and think they are so risk averse that they always over estimate the wind / conditions.

Now I know the solent has its own weather peculiarities, but I had an example earlier in the summer exactly like the one you mention where the met office were predicting a sw 5-6 though others were suggesting SE 10-12 knots. In that instance the met office were wrong. I tend to look at Simon keeling site, met check, weather online and xcweather. To be fair, if I was crossing the channel I would still look at the shipping forecast (and maybe that's me covering my backside,,,,just like the met office. Out of interest I think today's shipping forecast for the Wight area was force 3-4 and I doubt it got anywhere near that strength

 

[GHA]

Which coastal forecast?

Inshore:
[h=2]Selsey Bill to Lyme Regis[/h][h=3]24 hour forecast:[/h]WindVariable 3 or less, becoming northerly 3 or 4 for a time.Sea stateSmooth or slight.WeatherFair.VisibilityGood.
[h=3]Outlook for the following 24 hours:[/h]WindVariable 3 or less, becoming northwesterly 3 or 4, backing southwesterly later.Sea stateSmooth or slight.WeatherFair.VisibilityGood, occasionally moderate.

 

[jac]

Which coastal forecast?

Inshore:
[h=2]Selsey Bill to Lyme Regis[/h][h=3]24 hour forecast:[/h]WindVariable 3 or less, becoming northerly 3 or 4 for a time.Sea stateSmooth or slight.WeatherFair.VisibilityGood.
[h=3]Outlook for the following 24 hours:[/h]WindVariable 3 or less, becoming northwesterly 3 or 4, backing southwesterly later.Sea stateSmooth or slight.WeatherFair.VisibilityGood, occasionally moderate.

The actual coastal waters forecast.
http://www.bbc.co.uk/weather/coast_and_sea/coastal/11#selected-location sorry iPad won't let me paste the text but wind in the pm is talking about force 2-5. From 18:00 it mentions max gusts of 25 knots declining to 23.

Actually the inshore waters forecast makes the inconsistency even worse. It basically agrees with the GFS and the land forecast from the met office so how can the coastal one be so different.

 

[Twister_Ken]

Actually the inshore waters forecast makes the inconsistency even worse. It basically agrees with the GFS and the land forecast from the met office so how can the coastal one be so different.

Bear in mind that sea areas are BIG, so that what's expected to happen on your bit of the coast may be very different to the expectation 100 miles away.

 

[jac]

Bear in mind that sea areas are BIG, so that what's expected to happen on your bit of the coast may be very different to the expectation 100 miles away.

Fair enough but the coastal region is fairly small. Silent and Christchurch bay so about 40 miles. That was forecasting gusts of f6 and average wind of f2-f5

If accurate, why were the same strengths not forecast in the inshore forecast, even with the words locally inserted.

 

[Sandy]

Weather forecasting is not an exact science, yet.

Meteo Maritime, the French service has much smaller coastal areas than the Met Office and I find their forecast is much closer to what I am experiencing.

Based on this I took the RYA Weather book on holiday this year and sat with the synoptic charts and tied up what was said in the book along with what was forecast and shown on the chart. It was surprisingly accurate! I've come to the conclusion that the Met Office are correct BUT you need to apply some rules to come to what you are experiencing at sea level. The French do all that for you.

 

[jac]

Weather forecasting is not an exact science, yet.

Meteo Maritime, the French service has much smaller costal areas than the Met Office and I find their forecast is much closer to what I am experiencing.

Based on this I took the RYA Weather book on holiday this year and sat with the synoptic charts and tied up what was said in the book along with what was forecast and shown on the chart. It was surprisingly accurate! I've come to the conclusion that the Met Office are correct BUT you need to apply some rules to come to what you are experiencing at sea level. The French do all that for you.

Appreciate it's not an accurate science but just sounded odd that one forecaster could issue such different forecasts for the same area. Surely the base data / analysis is the same in one organisation.

 

[oldvarnish]

Surely the base data / analysis is the same in one organisation.

With luck, Frank Singleton will be along to explain that.

 

[Sandy]

Appreciate it's not an accurate science but just sounded odd that one forecaster could issue such different forecasts for the same area. Surely the base data / analysis is the same in one organisation.

Goodness no, in my line of work we have as many interpretations/solutions to the data as we have staff, sometimes even more. I am sure they are just the same up the road at the Met Office.

 

[jimbaerselman]

You're comparing a land forecast wind with a sea forecast wind?

Surface effect will halve the windspeed if there's little turbulence . . and sea breeze effect will modify it . . . and local terrain may channel it . . . or block it

 

[jac]

You're comparing a land forecast wind with a sea forecast wind?

Surface effect will halve the windspeed if there's little turbulence . . and sea breeze effect will modify it . . . and local terrain may channel it . . . or block it

Comparing two forecasts for sea from the same forecaster (coastal and inshore) coastal forecast is more tightly focussed areas and for 3 miles offshore.

Just odd that the coastal forecast was so different to inshore and land, not just in windspeed but also coastal forecasting heavy rain whereas the inshore forecast and land and GFS all said the same of being dry.

Inshore and GFS and land forecasts were all about right as it turned out. Gusts up to about 10 knots true, significantly less than the 25 knot gusts forecast by the coastal forecast

 

[Twister_Ken]

Comparing two forecasts for sea from the same forecaster (coastal and inshore) coastal forecast is more tightly focussed areas and for 3 miles offshore.

Just odd that the coastal forecast was so different to inshore and land, not just in windspeed but also coastal forecasting heavy rain whereas the inshore forecast and land and GFS all said the same of being dry.

Inshore and GFS and land forecasts were all about right as it turned out. Gusts up to about 10 knots true, significantly less than the 25 knot gusts forecast by the coastal forecast

I'm a little confused here. What is a coastal forecast and who issued it? I assume this is not the same as the Inshore Waters or the Sea Area forecasts issued by the MetOffice.

GFS forecasts are untouched by human hand and are computer prognostications, whatever name (WindGuru, X-country Weather, etc) they masquerade under, whereas MetOffice forecasts are made by actual human forecasters attempting to add intelligence and experience to the raw data churned out by machine.

 

[alahol2]

I'm a little confused here. What is a coastal forecast and who issued it? I assume this is not the same as the Inshore Waters or the Sea Area forecasts issued by the MetOffice.

The Coastal Forecast is on the BBC Marine weather site. http://www.bbc.co.uk/weather/coast_and_sea/coastal.
It doesn't actually say on the site who provides this forecast and there is no mention (that I can find) on the MET office site of a coastal forecast.
I do check this forecast from time to time and am often surprised at the magnitude of the 'Max gust' figures quoted.

 

[Daedelus]

Had similar with the forecast for the Friday of the Americas cup shenanigans at Portsmouth.

Risk of F8 the forecast said. In the event the rain was unrelenting but the wind was barely enough for the Cats to get up on their foils.

 

[lpdsn]

I'm another one that's lost confidence in the Met Office. I prefer to use the models and add my own fiddle factors.

Luckily for the Irish Sea the ECMWF forecast is available as well as the GFS (on the Met Eireann website) but as far as I'm aware not available in the UK despite being produced in Bracknell: http://www.met.ie/forecasts/5day-ireland.asp

What is really frustrating is that there are other more detailed models available that the forecasters have, yet they still produce broad-brush exaggerated forecasts. This detailed model from Ireland show the sort of thing that exists (And I find it does mirror some of my own fiddle factors that I add to the GFS/ECMWF based on experience): http://www.met.ie/forecasts/short-range.asp

 

[matt1]

I'm another one that's lost confidence in the Met Office. I prefer to use the models and add my own fiddle factors.

Luckily for the Irish Sea the ECMWF forecast is available as well as the GFS (on the Met Eireann website) but as far as I'm aware not available in the UK despite being produced in Bracknell: http://www.met.ie/forecasts/5day-ireland.asp

What is really frustrating is that there are other more detailed models available that the forecasters have, yet they still produce broad-brush exaggerated forecasts. This detailed model from Ireland show the sort of thing that exists (And I find it does mirror some of my own fiddle factors that I add to the GFS/ECMWF based on experience): http://www.met.ie/forecasts/short-range.asp

Agree...many other forecasters have increased granularity eg (iirc) meteomfrance will talk about the wind strengths at different parts of the day and of course the models can almost provide a by the hour level of detail. I think the met office haven't moved with the times in that regard. The bog standard 24hr time period they use requires them to include the highest wind speed expected in the duration.

 

[Leighb]

The bog standard 24hr time period they use requires them to include the highest wind speed expected in the duration.

I agree with much that has been said here, and find meteoconsult uk very useful, but in fairness the ISWF does often qualify the 24hr forecast with terms such as "at first" and "later" to give some idea of changes during the 24hrs. A significant factor is that they are using quite large areas compared with meteoconsult and if, as many here are, sailing mainly within 3-5 miles of the coast the "out to 12 miles" may often add a wind strength to the forecast. It all depends on wind direction relevant to the coast in question.

 

[keithgdg]

Passage weather .com is the best

 

[Leighb]

Passage weather .com is the best

As in the one you tell your crew, or more accurate?