Very useful new weather forecast resource

[conachair]

Originally Posted by roland stockham

Still 'just a grib' but with computer generated highlights. A very useful touch but still no input from a forecaster. The level of experience behind the guy with the crayon begins to make it a forecast. I would go with this as an improvement to a grib but still use the USCG Wx service as the main source of weather info. My rule is that if it doesn't show fronts it's not a forecast. Since the navy give us their professionally produced forecasts every 6hr for free why wouldn't you use them?

Do gribs have level of confidence in the model hidden in the data? Haven't come across it. Wfax don't tell you level of confidence either.

I like having radio fax as well offshore, probably in preference to gribs should only one be available but that's more to do with area download size realistically available . No one has said you aren't allowed to use everything and anything available. the OpenCPN weatherfax plugin is very good for overlaying wfax on grib on Sat image to see how they tally up.
Remember wfax are very much gfs based so you're looking at pretty much the same thing as gribs (according to a post on here anyway)

[roland stockham]

Originally Posted by conachair

Do gribs have level of confidence in the model hidden in the data? Haven't come across it. Wfax don't tell you level of confidence either.

Gribs are raw data so do not have any 'level of confidence' They compile information and display it but it is up to you to make the predictions. The 'forecast' for gribs ar computer created projections of the data trends. The grib service was created to provide data for weather forecasters.
Wx does have a level of confidence since the chart was produced by a forecast service (usually a national meteorological service) though they may not include it in the forecast!

I like having radio fax as well offshore, probably in preference to gribs should only one be available but that's more to do with area download size realistically available . No one has said you aren't allowed to use everything and anything available. the OpenCPN weatherfax plugin is very good for overlaying wfax on grib on Sat image to see how they tally up.
Remember wfax are very much gfs based so you're looking at pretty much the same thing as gribs (according to a post on here anyway)

No Wx is a totally different service. The original grib data has been interpreted by a team of professional weather forecasters who will look at different models and add additional information such as the position of fronts, tracks of systems, patterns such as the ITC and jet streams to come up with the best forecast they can. It is like the difference between talking to a physician and reading a medical text book. Same information but with or without the professional interpretation and experience.

That's my take anyway, others may disagree

[Paul L]

Originally Posted by roland stockham

Still 'just a grib' but with computer generated highlights. A very useful touch but still no input from a forecaster. The level of experience behind the guy with the crayon begins to make it a forecast. I would go with this as an improvement to a grib but still use the USCG Wx service as the main source of weather info. My rule is that if it doesn't show fronts it's not a forecast. Since the navy give us their professionally produced forecasts every 6hr for free why wouldn't you use them?

It's more than just a grib because it is an ensemble. This means it is the result of multiple models. I could not see how they calculate the probabilities on their site. One way is to use the differences between the models.

[roland stockham]

Originally Posted by Paul L

It's more than just a grib because it is an ensemble. This means it is the result of multiple models. I could not see how they calculate the probabilities on their site. One way is to use the differences between the models.

That what all gribs they assemble to data from all the different observation sites and provide a unified data stream that is some 'average' of all of it. Different sites presumably have different ways of turning that into a map.

I am not trying to say that anyone should or should not use gribs. I do and find them very useful. My concern is that some people don't seem aware of the difference between the sources of weather information and treat them all the same. I also find that some gribs supply a level of detail on the map that is not justified by the data an don' make clear what level of interpolation they are using.

Franks weather give a very good synopsis of what gribs are and there uses and limitation for sailors
What are GRIB files? - Franks-Weather - The Weather Window

[Paul L]

Originally Posted by roland stockham

That what all gribs they assemble to data from all the different observation sites and provide a unified data stream that is some 'average' of all of it. Different sites presumably have different ways of turning that into a map.

I am not trying to say that anyone should or should not use gribs. I do and find them very useful. My concern is that some people don't seem aware of the difference between the sources of weather information and treat them all the same. I also find that some gribs supply a level of detail on the map that is not justified by the data an don' make clear what level of interpolation they are using.

Franks weather give a very good synopsis of what gribs are and there uses and limitation for sailors
What are GRIB files? - Franks-Weather - The Weather Window

I think you are misunderstanding what a forecast grib is. It starts with an initial condition, the current actual weather reports. These are fed into a mathematical model that predicts the future conditions. There are many models in use. As I understand it an.ensemble uses the outputs from multiple models.
So you can then look say 4 days ahead and compare the closeness of the models. Less divergence yields a higher likelihood of being correct. All of the bureau forecasters start by using the models

[Alita49DS]

Sadly only does oceans. Not a lot of use for the Med.

[conachair]

Originally Posted by Alita49DS

Sadly only does oceans. Not a lot of use for the Med.

Only just come online, stills says experimental.

[roland stockham]

Originally Posted by Paul L

I think you are misunderstanding what a forecast grib is. It starts with an initial condition, the current actual weather reports. These are fed into a mathematical model that predicts the future conditions. There are many models in use. As I understand it an.ensemble uses the outputs from multiple models.
So you can then look say 4 days ahead and compare the closeness of the models. Less divergence yields a higher likelihood of being correct. All of the bureau forecasters start by using the models

I fully understand what a grib is my only point is the one you make highlighted above. These are fed into a mathematical model that predicts the future conditions. This is, I think, important. I think a lot of people do not realize the difference between this type of projection and a forecast made by a meteorologist. Meteorological forecasts start with the same data but are complied and interpreted by a professional forecaster. If you don't think that makes a difference fine, but I think it adds significant value.

[belizesailor]

Cool stuff. Thanks for posting.

[belizesailor]

Originally Posted by S/V Illusion

Quite correct. The latter requires some thought and insight with a bit of experience. Such was the state of the art in those days (twentieth century).

...and now a bigger box of crayons, to do the 10% increment probability ranges. [emoji6]

[Paul L]

Originally Posted by roland stockham

I fully understand what a grib is my only point is the one you make highlighted above. These are fed into a mathematical model that predicts the future conditions. This is, I think, important. I think a lot of people do not realize the difference between this type of projection and a forecast made by a meteorologist. Meteorological forecasts start with the same data but are complied and interpreted by a professional forecaster. If you don't think that makes a difference fine, but I think it adds significant value.

Certainly lots of confusion on Gribs out there. The biggest one I see is when people claim how some companies display is more accurate than.another display when in reality they are based on the same Grib file.

It's nice to have a forecasters presentation beyond just a grib. I use them for planning a passage. For me, I find gribs just fine and sufficient while on passage.

[roland stockham]

Originally Posted by Paul L

It's nice to have a forecasters presentation beyond just a grib. I use them for planning a passage. For me, I find gribs just fine and sufficient while on passage.

I go the opposite way round but that is because I use the SSB to get Wx on passage and don't have a radio modem. Wx reception is often poor in harbour but I can get Wifi for grib's which also give longer range (even if it is rather speculative beyond day 3)

[billdre]

I don't sail beyond coastal areas. But for me the issue of predicting weather isn't the format of the data but what model is being used. So rather than look at grib's I'd rather have the help of SailFlow or Windyty or other services that tell you which model is being used and you can select results.

[Paul L]

Originally Posted by billdre

I don't sail beyond coastal areas. But for me the issue of predicting weather isn't the format of the data but what model is being used. So rather than look at grib's I'd rather have the help of SailFlow or Windyty or other services that tell you which model is being used and you can select results.

Sailflow and Windy are displaying Gribs obtained from.various suppliers.

[roland stockham]

Originally Posted by Paul L

Sailflow and Windy are displaying Gribs obtained from.various suppliers.

Looked at sailflow and they have a 'professional' service for subscribers which may be a meteorological forecast. They also repeat the US coast guard forecast but why pay for stuff that is available free in other places?