GRIB files

I think 90% of offshore/long distance sailors use them. I find them remarkably accurate once offshore and very helpful for routing. I of course always reference them against one forecast from a real person. On a typical day at sea I would download the grib and a text forecast from the relevant met office (and listen to Herb if doing an W to E Atlantic crossing).

For more localised sailing like the English channel, land and thermal effects will have a big influence and will not be picked up (especially by the GFS model which is large scale and models the whole world). So not as useful but still worth looking at. On a typical cross channel sail I'll have a met forecasts and the gribs for my forecast.
 
GRIB is a standard for sending meteorological data. The data in a particular GRIB file will depend on the source; usually one of the well known forecasting models. So, it is more important to ask "How reliable is the forecasting model that is being used to produce this GRIB file?" Simon of this parish is better able than I to answer that than anyone else here!
 
Magnum said:
Does anyone routinely use GRIB files for weather prediction? If so how useful or accurate do you find them?
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I have found www.grib.us files to be more reliable than the forecast models on various websites.

The only concern I have had with them is at key coastal places, headlands and channels for example, where the software tries to differentiate between windspeed over water and over the land. On the cusp in between, it its not so certain.
 
Great source of weather data for offshore sailing, outside of coastal influences and are particularly useful if you have a fairly low bandwidth sat connection. Mailasail provides a very good service which is automated and can be viewed either on the boats chartplotter software or standard pc viewer. If bandwidth not an issue then passageweather.com gets my vote every time. In the Med last year we did download weather fax from our SSB receiver to supplement the gribs with a synoptic chart but not necessary if you have a good sat connection.

On our last transat the grib files via the mailasail server represented pretty much what we go!!
 
Antarctic is right. The models of course can make a big difference. However, a mesoscale model for the UK and most parts of Europe is not available for free. 90% of all the free stuff out there is based on the American GFS model (with wave heights from their navy's WW3 model).
Grib.us is based on GFS/WW3 as is the excellent passageweather.com (although if i remember correctly there other models available as well).
The excellent sailmail system has a few alternative models as well.

Good intro to all this stuff on:http://weather.mailasail.com/Franks-Weather/Home
 
I started using them june last year, and found that they were quite accurate for the weather systems which were coming across low after low every 48 hrs or so during july and august, in the northwest last year.
 
AntarcticPilot said:
GRIB is a standard for sending meteorological data. The data in a particular GRIB file will depend on the source; usually one of the well known forecasting models. So, it is more important to ask "How reliable is the forecasting model that is being used to produce this GRIB file?" Simon of this parish is better able than I to answer that than anyone else here!
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OK understood. We have the ability to overlay GRIB data on our B&G plotter. We don't need a viewer. Just the ability to download the files onto a USB stick which will plug directly into the plotter.

With this in mind what would you say was the best source of GRIB data? www.grib.us ? Is their a difference between the quality of free or paid for data?
 
Quoting from Frank's website

Output from GRIB files can look very impressive but it is necessary to remember the warning on my main GRIB page. Many GRIB file services simply relay output from NWP models, usually, but not always, the US General Forecast System (GFS) model. Therefore, none will be better than others in terms of reliability nor will any give more "accurate" forecasts than another.

There will be differences in presentation, ease of access and in the data offered, whether it be from a commercial service or a free one
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It seems there is little difference but AP may differ.
 
Magnum said:
With this in mind what would you say was the best source of GRIB data? www.grib.us ? Is their a difference between the quality of free or paid for data?
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Grib.us data is uncompressed. This is real money if a satellite phone is used. There are others out who offer compressed data like zygrib or theyr.
 
Saildocs, which is a free service provided by Sailmail takes a bit of learning but very good. Check out:http://www.saildocs.com/ Also explained on Frank Singleton's web page. With sailmail the actual email package makes document retrieval super easy. Can't remember now but perphaps you can use the software package to retrieve for free?
 
The mailasail service provides a compressed file which you can then transfer via a stick to your B&G plotter although to be honest you will find it easier just to read on the laptop.
 
GRIB Readers

Magnum, if your B&G package includes the "Deckman" software package then this will take your GRIB files on the laptop. What you need re GRIB files is a site that enables you to download a series of files eg 24, 48, 72, 96 hours so that you can animate the data on your system/reader to get a good indication of wind trends. Never a 100% solution due to the dynamic nature of weather systems but a risk level that is quite ok for, lets say, a go/no-go decision re a Biscay crossing.

Take a browse on Ed's site http://www.mailasail.com/ which offers not only a commercial service (good value) but good references/tutorial.
 
Magnum - in case your interested Simon Keeling, the weather guy of this parish, runs some weather courses that discuss the use of gribs amongst other things. Can't remember his website but I'm sure Google will bring it up.
 
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