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2015-03-16 20:29:54

Re: RTW start

Board » Sailonline Race Committee » Races

will you?
2015-03-16 17:26:18

Re: RTW start

Board » Sailonline Race Committee » Races

Well Done! It was the right decision to make. One of the reason SWR is the main event of SOL year is that we really get to test ourselves against the top navigators. And with 18 hours of headstart (and a totally different wx configuration) it would have been a pity to race this one on our own.

Thanks to the SRC and management for the reaction in such a short time!
2015-03-16 13:08:57

Re: RTW start

Board » Sailonline Race Committee » Races

It appears that we are starting despite the new postponement of the IRL race. I am in total disagreement with this decision as it makes incomprehensible the first postponement. Hope that the SRC can reconsider and delay the start accordingly.
2015-02-19 16:46:03

Re: The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

In synoptic conditions, i.e. wind given by large pressure systems, forecast are simpler and more reliable (see the Bos-New race with the heavy storm). In fluky conditions, with basically no pressure gradient, wind is given by "local"effect such as cloud coverage etc. So yes, on mesoscale, weather is less "consistent".

As a comparison, GFS is "averaged" over a much bigger gridsize, so all the small scale variation are zeroed and you ave a more stable but less interesting windfield. On the other hand NAM model, on a 0.1deg scale, has the same behaviour.
2015-02-17 07:01:29

Re: The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

JB,
at present time we have to allow for some WX data outside the race course (the purple line). This to allow predictor to work properly in the client. In this race we have used 0.5deg from each side. In the end we had more than 30% of datapoints "useless" for the race. In an optimal condition (no points outside race area), wxfile should have been around 4MB, which travels compressed now, so perfectly usable for the "desktop" client.
Regarding mobile, probably it has some problems (depending on hardware) regarding memory and cache. Probably Zappe can look into that.
Finally, the WRF is defined every hour, so dataset is 3X for the same resolution compared to GFS. As outlaw commented, we should push for even higher time resolution (1 frame every 15min). In this case probably we'll have denser frames for the first 6hrs and sparser afterwards.
Ciao
a.
2015-02-13 11:14:02

Re: The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

forecast for sunday morning
2015-02-11 14:37:14

Re: The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

A small video on high resolution weather

http://youtu.be/n5ThrmvMJxA
2015-02-10 21:30:23

Re: The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

so, you are referring to the grid discretization.
In SOL this changes from race to race. Usually we start from 0.5x0.5 deg GRIB file from NOAA which is then interpolated to the grid of our interest. In Leg4, for the first time, we are running the ocean on a 1x1 deg grid. The "pointy" edges are caused by the interpolation algorithm (bilinear), which is the same we use to get wind in between grid points.
The WRF model we are using in the BOS-NEW race is evaluated on a much denser grid. This is not an interpolation process but a complete physical evaluation. The 0.5degx0.5deg GRIBS from NOAA are taken as boundary and starting conditions then the calculations are done on a powerful computer. The result is a 0.05X0.05 deg GRIB.
2015-02-10 07:39:06

Re: The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

We have also higher time resolution with WRF. GRIB frames are spaced 1hr instead of 3hrs. This can help with faster gradients.

@A2: I don't really get your point regarding quadrants. Can you explain?

--- Last Edited by ita10267 at 2015-02-10 07:41:17 ---
2015-02-09 08:28:44

The Weather Research & Forecasting Model (WRF)

Board » Technical Discussion

We are proudly introducing the WRF Model as a new source of weather forecast data (GRIBs). WRF is recognized throughout the scientific community as the most accurate and reliable weather forecast model. An extensive (and technical) description of WRF can be found at:

http://www2.mmm.ucar.edu/wrf/users/model.html

The scope of this post, without entering into too much technical details, is to inform the SOL community about the features that this model can introduce and how we can benefit from it.

In SOL we historically use the GFS weather model. According to its definition the GFS model is basically one “of the predominant synoptic scale medium-range models” in general use. Therefore it is good (within its accuracy which is around 30km with the resolution we are currently using) if wind is dictated by pressure/temperature fields. This means that, in shorter races, we rely on a small number of grid points and, in between them, we use interpolation. The result is a smooth wind field that is hardly able to follow coastlines. Of course we miss all the finer features that come within this scale, like funnelling, day/night breeze, swirls etc.

We therefore decided to propose a trial of the WRF model, which is a local weather forecast that takes into account a number of small scale (accuracy in the 10m range can be reached) factors neglected in the GFS model. This is not an exhaustive list but a few of these factors are:

- Landmass elevation profile
- Urbanization
- green fraction
- soil composition (as sand heats differently from clay, concrete etc etc)
- ground heating
- sea heating

So, many new local effects can be visible by SOL users. Of course, for those who are not aware about basic meteorology, there will be no difference in sailing with the old GFS model compared to the new one other than a more “realistic” feeling and less smoothed appearance of the wind field. The experienced sailor, on the other hand, will recognize the patterns he is usually able to see IRL. So, overall, we believe that the realism of SOL can be improved and increased by the new wx source.

We have decided to test drive the new model on a classic run between Boston and Newport. For this purpose a 0.05deg spaced grid will be used. This is 10X more accurate than the most accurate GFS grid we have ever used. As a drawback, given the additional computational time and with the purpose of keeping update times consistent with the GFS model, a shorter maximum time window of only 2.5 days is available for the weather forecast as seen when moving the slider at the bottom of the client.

Please take your time to explore the new wind data and post your feedback here in this thread.

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