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Author Topic:   GRIB Weather Data
jimh posted 08-20-2014 10:18 AM ET (US)   Profile for jimh   Send Email to jimh  
Weather data is available electronically on-line and for download in the GRIB format. GRIB stands for GRIded Binary data, and provides meteorological forecast data in several formats. The GFS or Global Forecast System GRIB data is very useful for graphic display of future weather patterns, such as pressure, temperature, wind speed, and precipitation.

I have been using the features of PolarView NS, a chart plotter program, to download and display GRIB weather forecasts while boating. GRIB data is available in increments of 3-hours into the future, and is localized for 0.5-degree of latitude and longitude.

It was recently mentioned to me by Don J that the new SIMRAD NSS Evo2 chart plotter can display and overlay GRIB data onto its navigation chart presentation. The SIMRAD cannot download the data itself, but can read GRIB files from a storage volume such as a memory card. By using a computer to download the GRIB files from a GRIB server on the internet, and then copying the files to a memory card, GRIB data can be brought to the SIMRAD device for display.

I also just discovered that it is possible to view GRIB data at the fantastic website of the WEATHERUNDERGROUND, using their very sophisticated WUNDERMAP product. Visit WUNDERMAP at

On the right side of WUNDERMAP there is a long table or list of features that can be shown on the map display. Turn off the usual RADAR and WEATHER STATION features, and scroll down the list to the option MODEL DATA. Turn on MODEL DATA. Adjust the OPACITY with the slider. Click the RUN button, or drag the slide to a future time. The GRIB data is displayed over the map. Using the MAP TYPE option set to WIND, you can see predicted wind direction and speeds. The default setting is MSL. MSL usually means "mean sea level." I am not quite certain what the map shows with the MSL feature, but it appears to be related to atmospheric pressure. (Maybe a meteorologist can help us understand it better.) You can also view precipitation type.

The advantage of GRIB data is its localization to a 0.5-degree region and its incremental forecast in three-hour steps. Having this sort of detail can help locate short periods of lower wind or fair weather in otherwise windy and rainy days.

The WUNDERMAP is a rather intensive web page presentation, and it may not render well on small screens or be as useful on very slow internet connections. It is a great tool if you have a high-speed internet connection and a large display.

Jefecinco posted 08-20-2014 10:54 AM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Another feature of the Weather Underground site is that it shows the location of the weather stations in the area of your interest and allows you to display the current conditions at the station of your choice. In our local coastal area conditions can vary considerably at locations only a few miles apart. It's nice to be able to check conditions at locations other than the local airport.

In general I experience more accurate forecasts from the Weather Underground than from the Weather Channel or the NWS.


Hoosier posted 08-20-2014 01:59 PM ET (US)     Profile for Hoosier  Send Email to Hoosier     
In the FWIW department Weather Underground is owned by the Weather Channel.

This is an neat animation of GRIB data

its companion for Great Lakes Currents is here:

Hoosier posted 08-20-2014 02:00 PM ET (US)     Profile for Hoosier  Send Email to Hoosier     
Ooops html
Jefecinco posted 08-20-2014 07:19 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
I got the idea somewhere that Weather Underground was sponsored/operated/owned by a university??? I wonder where that came from.


jimh posted 08-20-2014 09:22 PM ET (US)     Profile for jimh  Send Email to jimh     
The attractive part of the GRIB weather data is that you can carry it with you in a very compact file format, and you do not have to be on-line with a high speed connection to use the data. We do a lot of boating in places were an internet connection, if available, is not very high speed, and looking at some presentations of GRIB data on-line will be difficult.

I thought it was quite unusual that the SIMRAD chart plotter could display GRIB data. I have not investigated this at all. I wonder if any other chart plotters can do this? For example, can GARMIN chart plotters load and display GRIB data?

jimh posted 08-20-2014 09:40 PM ET (US)     Profile for jimh  Send Email to jimh     
David--That wind animation seems to only show the present wind. It has no forecast data. I can already figure out the present wind--it is the future wind that I an interested in getting information about from GRIB models.
Hoosier posted 08-20-2014 09:55 PM ET (US)     Profile for Hoosier  Send Email to Hoosier     
Correct. Their disclaimer is that it was an "art" project to animate the GRIB data to show current wind conditions. Right now I wouldn't want to be on Lake Michigan with all that flow coming up from the south. I think it's a pretty neat piece of software.
swist posted 08-23-2014 08:43 AM ET (US)     Profile for swist  Send Email to swist     
Before I start using it to make important decisions based on the weather, I would sure like to know the background of the Weather Underground. It does seem to have better products than NOAA/NWS. It can't possibly be owned by The Weather Channel, which consistently sacrifices accuracy for sensationalism (gotta please those sponsors). Some university project seems more likely, but where is their funding coming from? This is not simple software they've developed.
Hoosier posted 08-23-2014 09:19 AM ET (US)     Profile for Hoosier  Send Email to Hoosier     
If you look at the very bottom left of the Weather Underground background page

page you'll see this:

"Copyright © 2014 The Weather Channel, LLC"

They also own WSI and Intellicast. I think the only internet weather site they don't own is Accuweather.

"Who is
Since 1996, has provided expert weather information to weather savvy users. With the most technically advanced site-specific weather forecasting system in the world today, the result of a multi-million dollar research project, delivers site-specific forecasts for 60,000 sites in the U.S. and around the globe. From detailed local forecasts to hurricane tracks, severe weather warnings to international conditions, has the active weather tools business professionals and outdoor enthusiast have come to rely on, consistently making us one of the top five weather sites on the Internet.

Who is The Weather Company?
The Weather Company (TWC) includes:

Broadcast Division – The Weather Channel, as well as products for radio, newspapers, digital cable services, and interactive television

Digital Division –,, and products for broadband and mobile platforms

Professional Division – premier business-to-business weather services, particularly for the media, aviation, insurance and energy sectors

The Weather Company has become renowned for its ability to successfully combine the power of unparalleled industry knowledge, the experience of an unprecedented number of meteorologists and five state-of-the-art Global Forecast Centers. TWC’s internationally recognized experts in tropical weather, climatology, and severe weather apply their skills to cutting-edge technologies designed to constantly improve our abilities to forecast, detect and visualize the disruptive weather events that affect the safety and property of our clients and their customers. The Weather Company is owned by a consortium made up of NBC Universal and the private equity firms The Blackstone Group and Bain Capital."

All that said, so what? They all get their source data from the NOAA and then post process it to make it pretty in various "consumer" packages. If you dig deep enough in the NOAA sites it's all there.

swist posted 08-23-2014 06:30 PM ET (US)     Profile for swist  Send Email to swist     
"If you dig deep enough in the NOAA sites it's all there."

It has to be - that's what prompted my question - the resources required by the NWS are considerable (manpower and weather simulations using vast amounts of computing power), it doesn't seem likely some "underground" group is doing its own thing.

jimh posted 08-24-2014 08:51 AM ET (US)     Profile for jimh  Send Email to jimh     
The GRIB models you can download use the same forecasting data that most of the "weather" website use to create their forecasts. The beauty of GRIB data is that it is localized to 0.5-degree of latitude and longitude, and provided in three hour increments. The "weather" sites say "50-percent change of rain," but GRIB tells you when the rain will occur, within three hours and within about 100 miles.
Hoosier posted 08-26-2014 09:30 AM ET (US)     Profile for Hoosier  Send Email to Hoosier     
Here's an example of "digging deeper". I get this page, sometimes, when I click on the "Read More" under the forecast summary at the top of my local forecast page:

I said "Sometimes" because the NWS software assigns links based on what's going on, so sometimes you get taken to the tropical page if there's a tropical storm going on, or to Norman, OK, if there are Tornado conditions.

jimh posted 08-28-2014 11:26 AM ET (US)     Profile for jimh  Send Email to jimh     
GRIB data in the GFS format gives me what I really want to know:

--the predicted wind speed and wind direction

--the predicted precipitation

GRIB gives this to me in three-hour increments and in localized position to 0.5-degree (35-mile) resolution.

When I am cruising I try to update the GRIB model data every day, so that the forecast predictions of the model are for a shorter time into the future. Since the GRIB data is actually a very compact binary file, the GRIB data can be accessed and downloaded easily, even on very slow and long-latency internet connections, which are the kind of internet connection that is often available when cruising in remote areas.

Forecast data in three hour increments with geographic localization to 35-miles is much more useful than the usual marine forecast available on VHF Marine Band radio broadcasts. A typical marine forecast might say something like:

"Wind south at 10 knots increasing to 15 knots after noon, then backing to southeast before midnight and decreasing to light overnight."

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