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Board » General Discussion » Weather - Brain Storm

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Posted by
bonknhoot


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2020-09-02 08:59:38 - Weather - Brain Storm
Recent chat in the M2O 2020 about the weather that we import into SOL has prompted this new thread, hoping that concerns and ideas may gravitate towards some sort of consensus or conclusion. Whether anything can be done with such a conclusion is another matter.
Remember: SOL is a 'cooperative' and everything that happens is done by volunteers. Any change in the fetching of weather is likely to require changes to the software (the racing engine) that runs on the server. This is no sinecure, and the volunteer resources that we have that can attempt this are scarce.
I'll get the ball rolling with a separate post about the status quo.
Clipping along
Posted by
bonknhoot


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2020-09-02 09:15:54 - Re: Weather - Brain Storm
Currently, we have the capability to fetch three sources for weather with the following 'tags' - global_gfs, nam_awip12 and wrfems, updating every six hours.
global_gfs is what we use most often and it is rough-and-ready. I'm not hugely familiar with meteorologist terminology but I think it is what is called 'synoptic', which I think means it is primarily based on surface pressure variation; in other words, there is no modelling of local coastal effects. The highest resolution we can fetch is 0.5 x 0.5 degrees, in other words the data - that is then interpolated by the server (or a router) - is given at nodes set 0.5 degrees of longitude and latitude apart.
0.25 degree resolution is in fact available, but we can't fetch it. With 0.25 resolution the amount of data describing the wind over space and time increases by a factor 4, and obviously routing or SOP-ing through this becomes commensurately trickier.
I'll write a second note later.
Clipping along
Posted by
Zorba777


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2020-06-06 08:22:54
2020-09-02 14:51:37 - Re: Weather - Brain Storm
Thanks for setting up this brainstorm, Jan. My concern is: what happens if GFS (or other WX sources we use) start updating every 3 or 4 hours? I have the impression that even with the every 6 hour updates it is already difficult for some people to combine SOL with their professional or family life (as well as sleep). So, maybe we can discuss that in one go.
But in keeping with my first question I want to submit this article which takes a good look at where weather forecasts could be going in the coming years. Some techniques seem to pave the way for accurate forecasts that are 8 times longer than we now have: https://metro.co.uk/2019/09/18/will-weather-forecast-ever-100-correct-10751641/
Posted by
bonknhoot


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2020-09-03 09:10:25 - Re: Weather - Brain Storm
That is a very interesting article, Dan, but I suppose it all depends on what NOAA consider 'accurate' or 'correct', when it is quoted to state 'a seven-day forecast is accurate around 80% of the time' or 'a five-day forecast is correct approximately 90% of the time'. One can imagine that the assertion is correct about something like 'it will rain in The Peloponnese tomorrow', but, as we know from experience, it doesn't imply that the wind strength and direction forecast for 120 hours ahead at a specific lat/lon posn will be re-forecast as exactly the same 6 hours on, now 114 hours ahead.
I would like to think that that sort of accuracy will remain impossible for very many years yet. So, that aspect of our game - forecast volatility and second-guessing the met service - is not much at risk, IMO.
I do agree with you that once gribbed free-issue forecasts become available with a frequency of every 3 hours, it would reduce the attractiveness of our game if the game were to fetch these every 3 hours as well. I see little reason (though not none) for simply keeping our own fetch frequency at 6 hourly; especially if 'accuracy' has improved anyway.
Indeed, I would suggest it could mean an opportunity to reduce our fetch frequency to every 9 hours, which would give everyone around the world a midnight WX every couple of days.
Clipping along
Posted by
bonknhoot


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2020-09-03 10:25:33 - Re: Weather - Brain Storm
My agenda is not so much a concern with ever more and better forecasts, but a concern with the rough-and-ready nature of global_gfs, our standard 'go to' weather. The question and the challenge I want to raise is 'Can we do better?'.
For the long distance ocean races, this question is not so important, as, out in the middle of the ocean, modulation for whatever should change little to a forecast, and because guessing what is the best thing to do given the uncertainty about what the wind will really be a week ahead will continue to be a challenge for SOLers.
It is the races of say 3 to 4 days maximum that I feel/find are or have become somewhat mathematically deterministic. You have to have the tools to do the math, but once you have such tools working for you, a race becomes primarily a "do" exercise.
Clipping along
Posted by
ij


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2020-09-03 17:24:22 - Re: Weather - Brain Storm
I'm sorry to spoil the party but I'd prefer to always sail on WRF weather. Obviously that's not "feasible" in the most straightforward manner for races over large areas. However, if it would be possible to limit calculating the wrf forecast only to areas where there are boats, where the boats can reach, and only calculate very short-term wrf, like 12h-15h (mostly to cover across a single wx update failure), it could bring down the amount of processing power needed for the forecasting.

So we'd be having sort of composite wx with a base layer of 0.25x0.25 gfs to visualize longer term forecast and act as a backup wx. Which parts of the base layer would be selectively replaced by wrf would be dynamically determined as the race progresses.

Whether we have computation capability to do that (or would be able to get the necessary processing capacity) I have know idea but I certainly would want to know how big area would need to be calculated. Even in ocean races boats tend to keep in packs (although wrf itself might impact the dynamics that typically lead to it with gfs). The biggest problem in this approch IMHO is the long tail of boats because they'd require disproportionate amount of the all processing.

If that turns out still infeasible, some additional filter could be applied which allows using wrf only under conditions where wx seems unstable (based on the corner wind components it's possible to estimate this I think) or when there's landmass.

It's very complex to realize technically though, we cannot even run the 0.25x0.25 gfs part of that currently so it may remain wishful thinking.

--
i.
Posted by
ij


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2020-09-03 18:11:38 - Re: Weather - Brain Storm
I agree with bonk that 80% reliability is really a joke. Even 90% is not really something I'd boast about. It's worth to remember the error starts to rapidly accumulate. It's unlikely to be dropping linearly but more like larger error also leads to much larger error accumulation (and thus uncertainty).

I've never seen the definitions of that kind of % metric anyway (so if somebody has pointers to some scientific papers evaluating forecast long-term accuracy, please, I might read myself). But I wouldn't be surprised if it turns out quite bogus or irrelevant to measure what kind of accuracy we're talking here.

--
i.
Posted by
ij


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2020-09-07 22:16:10 - Re: Weather - Brain Storm
Comparing 0.25x0.25 wx grid with 1x1 (I forgot to make the arrow density the same so please disregard that difference):

https://postimg.cc/F19n3Yjp

--
i.

--- Last Edited by ij at 2020-09-07 22:18:39 ---
Posted by
ij


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2020-09-09 21:00:45 - Re: Weather - Brain Storm
Just a minor note from some ECMWF validation report now that I came across one: in 10m wind at 5 days the frequency of large errors is around 4% (+/-1 due to year cycle) now so it's in ballpark with those 90/80% numbers. (And in temps slightly worse.)

GFS is likely somewhat worse than that given ECMWF is generally considered slightly better although both can be shown to be better in selected cases.

What is means to routing accuracy is hard to know without looking deeper into the report (if it's told at all). The distribution of the large errors over time matters too much. But if distribution would be uniform (it very likely isn't), one would very likely hit one large deviation in almost every 2 weeks long race. And how bad the large error % gets when consider beyond 5 days, no idea.

--
i.


--- Last Edited by ij at 2020-09-09 21:01:19 ---
Posted by
Zorba777


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2020-09-10 08:30:59 - Re: Weather - Brain Storm
Hi Bonk and Ij,

I don't know how accurate the weather models will become. Even the experts don't agree on that question. We can probably just agree that they keep getting better and look at possible consequences for SOL simulations.

I agree with Jan on the possible problem that shorter races are moving closer to "fixed solution". If there is only 1 (or even no) WX change during a race we are on a fixed weather map where good math tools can figure the winning route and then it just becomes a question of who executes that route more optimally. But some SOLers like that kind of challenge, so I wouldn't take that away.

If long term weather forecasts get more accurate then even the medium term (3-4 day) races would become more like sprint races where execution of near optimal route is more important than anticipation of weather changes.

In the long ocean races it will not be anytime soon that weather models can give us a near optimal route for more than 2 or 3 days. But if WX updates become more frequent then we would have to think about SOLers' sleep.
We can decide to skip some updates and only update the maps that SOL uses every 6 or 8 hours. But even in that case some players would gain an advantage by looking at the GFS updates we skip, because they will already show in what direction the weather is changing. Perhaps it would be more useful to change to a more detailed, but less frequently changing, source of weather data as ij suggests...

--- Last Edited by Zorba777 at 2020-09-10 08:47:58 ---

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