passage weather site what do these mean please

[fontmell]

Hi

I would be grateful if someone can explain in simple terms what these descriptions as found on Passage Weather and other sites mean and what difference is
thanks

GFS
COAMPS
SWS-CMI

 

[prv]

GFS is a weather model, so I would guess the others are too.

Essentially, it's the particular computer program that was used to make the prediction. They differ in their tradeoffs of accuracy, resolution, and computing power required. Afraid I don't know enough about them to say which is better for what.

Wait for Simon to come and give us chapter and verse

Pete

 

[Reverend Ludd]

Global Forecasting System
Coupled Ocean Atmosphere Mesoscale Prediction System
Comité Maritime International/Caribbean Maritime Institute

As has been mentioned above they are sources of weather data used to forecast weather.

 

[macd]

Go to www.passageweather.com.
Click on the 'FAQ' link at the top of the page.
Scroll down.

 

[billreilly]

Hi

I would be grateful if someone can explain in simple terms what these descriptions as found on Passage Weather and other sites mean and what difference is
thanks

GFS
COAMPS
SWS-CMI

GFS = Global Forecast System model, one of the operational forecast models run at NOAA/NCEP (Part of the U.S. National Weather Service)

COAMPS = Coupled Ocean / Atmosphere Mesoscale Prediction System model, Developed and run by the U.S. Naval Research Laboratory

SWS-CM1 = An advanced weather model developed and run by Sailing Weather Service, one of the world's most respected weather routing and consulting companies

As pointed out above, all models have their strengths and weaknesses, so none of these models is going to always be better than the others... it's best to have a look at the GFS and the higher resolution (SWS-CM1 or COAMPS) forecasts to get a better idea of what to expect... It's always good to have a second opinion...

I hope this answers your question...

Bill

 

[capnsensible]

This gives me an opportunity to mention that I use the site a great deal and I am very impressed.

No Relation! Just a happy user.

Thanks

CS

 

[franksingleton]

GFS = Global Forecast System model, one of the operational forecast models run at NOAA/NCEP (Part of the U.S. National Weather Service)

COAMPS = Coupled Ocean / Atmosphere Mesoscale Prediction System model, Developed and run by the U.S. Naval Research Laboratory

SWS-CM1 = An advanced weather model developed and run by Sailing Weather Service, one of the world's most respected weather routing and consulting companies

As pointed out above, all models have their strengths and weaknesses, so none of these models is going to always be better than the others... it's best to have a look at the GFS and the higher resolution (SWS-CM1 or COAMPS) forecasts to get a better idea of what to expect... It's always good to have a second opinion...

I hope this answers your question...

Bill

I would like to amplify what Bill has correctly said.

All numerical weather prediction models have to use global data and information predicted globally. Partly this is because weather can travel quickly – up to 50 knots over 24 hours and partly because of tele-connections. What happens in one area can affect weather a long way away. El Niño and La Niña are two well known examples of this.

The GFS is a global model and, like all global models, is constrained by data and computer power. It can only work on a ¼ degree (25 km) grid - although it only issues data on a ½ degree grid.. That means that it can only handle weather and topography on a scale of about 100+ km. It will generally do well for large scale patterns up to about 5 days ahead. See http://weather.mailasail.com/Franks-...ecast-Examples.

To try to predict smaller detail over shorter times, there are meso-scale models –COAMPS (US Navy), the UK NAE, HIRLAM and others run by such as SWS, Windguru, Windfinder, Theyr.com, Theyr, tv, Predictwind etc. All these have to take input globally and their accuracy will depend, ultimately on the prediction of large scale weather.

These meso-scale models use a variety of grid lengths. This is primarily so that local topographic effects can be taken into account. For example, Bill has said that SWS does well through the Gibraltar Strait but can be no better than the GFS over, say, the western Med.

When making comments or assessments of such GRIB forecasts, I always warn against confusing data quantity with real information. Some calculations may be doe on a 1 km grid allowing, in theory, definition of weather on a scale of about 5 km. However, that level of detail is very short-lived, even if it can be analysed on that scale – which it is not by the private sector models mentioned above.

COAMPS (I think), HIRLAM (probably), SWS (possibly), WindGuru (I think), UK NAE (definitely) use a grid of around 1/10 of a degree ie about 10 km. At best, that only can define weather on a scale of around 50 km. The lifetimes of such sized weather systems are around 24 to 36 hours.

Much more on these topics, fascinating to me if nobody else, is at http://weather.mailasail.com/Franks-Weather/Home. If you have problems in navigating the site, put “accuracy” into the site search engine.