XC Weather and the coming storm . . .

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Nick
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XC Weather and the coming storm . . .

Postby Nick » Fri Mar 01, 2019 9:39 am

.
Why does XC Weather more times than not predict a deadly storm at the end of its prediction range a week hence, a storm that inevitably moderates or disappears as the day approaches?

Any weather/prediction model experts have an explanation for this phenomenon? :rainonme
- Nick 8)

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wully
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Re: XC Weather and the coming storm . . .

Postby wully » Fri Mar 01, 2019 9:17 pm

It’s because they enjoy winding up windsurfers...

Ooooohhh.... it’s going to be windeeee guys.

Ah, no it’s not

Fooled you again.

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Re: XC Weather and the coming storm . . .

Postby Burst Boiler » Sat Mar 02, 2019 4:00 pm

Its a characteristic of the GFS model used by XC (and most of the free forecast sites), but its a real pain for passage planning. The French meteo-consult.co.uk site has a Compare Models function that shows what the GFS, Arpege and their own model predicts. GFS is often out of agreement with the other two at longer timescales.

The meteo site has other useful stuff like 10 miles offshore, sea state and also a Reliability Index to indicate when conditions are harder to predict ad they expect the forecast to change.

Its free although you can subscribe for more features, none of which are necessary really.

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Re: XC Weather and the coming storm . . .

Postby Burst Boiler » Sat Mar 02, 2019 4:16 pm

Probably best if I give a link. This is for Largs.

https://marine.meteoconsult.co.uk/marin ... 1198-0.php

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lady_stormrider
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Re: XC Weather and the coming storm . . .

Postby lady_stormrider » Wed Mar 06, 2019 8:26 pm

Metcheck has started to get pretty inaccurate as well - They keep predicting snow (it's only snowed once this winter) and why they think they are going to be accurate six months hence is beyond me.
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aquaplane
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Re: XC Weather and the coming storm . . .

Postby aquaplane » Thu Mar 07, 2019 1:45 am

Why they think they can be accurate six days hence is beyond me, the first 3 days may be close but after that it's a lottery.
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Re: XC Weather and the coming storm . . .

Postby Burst Boiler » Thu Mar 07, 2019 12:10 pm

At least meteo admits this by having a 65% reliability index for next Wednesday. In settled conditions in the summer, when longer forecasts are more reliable I've seen this a lot higher, but right now even 65% is probably optimistic.

As for metcheck, it more or less uses the same GFS model as XC (with a bit of fiddling) so will give a similar forecast to XC. My view of GFS is that for 3+ days, it gets the weather right but the timing and location wrong since it doesn't accurately predict the speed and direction of frontal systems. 30 knots predicted at Canna in 5 days time can end up hitting Jura in 4 days, etc.

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lady_stormrider
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Re: XC Weather and the coming storm . . .

Postby lady_stormrider » Thu Mar 07, 2019 7:51 pm

Just compared BBC Weather and Metcheck for my postcode just for tonight. There is a 4 degree difference - meaning it may freeze tonight (BBC) or be a bit cool (Metcheck).
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Re: XC Weather and the coming storm . . .

Postby Burst Boiler » Thu Mar 07, 2019 11:44 pm

The Beeb dumped the (UK) Met Office a couple of years ago in favour of the (French) meteo group which caused much spluttering into their warm beer down south. I've found the beeb's tv forecasts more informative as a result, with occasional mention of the jet stream, something the met office never did. The proper perspective is also restored to the uk maps so the south of England is no longer blown up relative to further north. Whether some people like the idea of the s of e being blown up is a different topic . . .

As my old gaffer used to say, all models are wrong, but some are useful. To me, the meteo groups models just seem more useful than most, but its always sensible to check out a few different models. If they all agree, you can have more confidence in them. If they all disagree, then its likely none of them are very reliable. In the end as sailors, we need to sail the conditions we find, and not sail to the forecast.

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Re: XC Weather and the coming storm . . .

Postby lady_stormrider » Sat Mar 09, 2019 9:42 pm

I've just had a Highland & Islands Weather Facebook page pop up on my stream. They are pretty accurate and Scottish-based, with lots of lovely graphs.

I should also point out that they have issued an early advisory for a spell of severe gales early next week - with the associated low pressure dragging cold Northerly winds bringing snow by next weekend :freezing .
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Re: XC Weather and the coming storm . . .

Postby BlowingOldBoots » Sun Mar 10, 2019 12:39 am

Why do we expect deadly accurate weather predictions? Personally, beyond, a few days is all that really matters anyway. I am more worried about the mess the Met Office have made of their website. It was perfectly usable and now it is a dogs breakfast.
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