This article will explain everything Australian fisherman need to know about weather sites including how
forecasts are made, why some forecasts are better than others and what data sources each weather site
Along the way we will bust common myths associated with weather and allow Australian fishermen to be
Its 2017 so we know most of you don’t want to read all this; it’s too long and dry, you just want the
answers right? In that case you can jump straight to our quick facts article HERE,
however if you do that you won’t understand what some websites actually do when they try and calculate
seabreeze or why BoM would confirm “Fish Ranger’s forecast data for VIC and TAS is better than that used
by MetEye and is able to reveal more detail than MetEye for these states”.
For those who want to understand weather forecasting and weather sites properly we recommend reading the
What is ‘The Weather’
When people talk about ‘the weather’ they are generally talking about two things – Observations and
Observations are measurements of weather taken by weather stations. In Australia there are currently 870
weather stations throughout the country.
These stations are fitted with instruments that enable them to measure wind, rain, temperature and
They are managed by the Bureau of Meteorology (BoM) and provide a network of current conditions around
Some stations record all weather variables while others record only some. Similarly, some stations
record values every 10 minutes while others 30 minutes and some only once or twice a day.
BoM make data from these stations readily available so when weather sites report on current conditions
or when the news reports maximum and minimum temperatures recorded for the day they are using data from
To see where these weather stations are located throughout the country you can look at the following
links for each state.
Forecasts are predictions of weather in future. They are made by computers that run mathematical models
which simulate changing conditions over time.
Data from these models is used to drive tables, charts and weather maps, or can be summarised into text
forecasts which provide an overview of expected weather conditions for a region.
How Are Forecasts Made?
In order for a forecast model to predict weather ahead it first needs to know what the weather is now.
Weather data from observation stations and other sources is collected and fed into the model as ‘initial
conditions’. These effectively provide a snapshot of what the atmosphere looks like at the current point
in time. The weather model then works out how
weather will evolve over time.
What is a forecast grid?
Imagine a series of dots laid out in a grid across Australia. Forecast models use laws of thermodynamics
and other laws to calculate how weather at one point will interact with weather at the next point and by
repeating this process over and over they can
work out what the weather will be at each point in the grid.
Once they get to the end they go back to the start and do it again for the next time step and so on until
there is a forecast for each point in the grid and for every time step. The sum of time steps is the
duration for which the forecast is valid, ie a 7
day forecast. Time steps are usually made in 1 hour or 3 hour intervals with the smaller interval being
better as it provides more data. At each iteration, the model uses expected values it just calculated as
initial conditions for the next time step so it’s easy to se
e how small deviations in expected values at the start of the models run manifest into larger deviations
at the end of the forecast period.
For this reason, forecasts are most accurate close to the present time and less accurate the further
they move away from the present time.
Forecast data files are often called ‘grid files’ because they contain a weather forecast for each point
in the grid for the defined region.
What is Forecast Resolution?
This is an important one so take note. The ‘Resolution’ of a forecast refers to the spacing between dots
in the forecast grid. The smaller the spacing, the closer the points are together and the higher the
forecast resolution. Higher resolution forecasts
are better guesses at what the weather will be than lower resolution models. These days high resolution
generally means grids with less than 10km spacing between points.
You can think about this like a television set. Old box style televisions had fewer dots per area than
modern high definition televisions which pack many more dots into the same space. Just like more dots
make for a clearer picture in television, more dots also make for a better forecast in weather
In the below images, the image on the left shows a forecast grid overlaid on Australia. The image on the
right shows a forecast grid overlaid on Australia where the dots are twice as close together, resulting
in a forecast with twice the resolution.
In general, the best forecast model is one that has the highest resolution and the smallest time step
because it contains the most amount of data for a given area.
Even modern super computers are challenged to process the quantities of data required for weather
forecasting hence the need for trade-offs between resolution, size of area being forecast and time
What is a Global Forecast Model and what is a Regional Forecast model?
Since weather is a global phenomenon you can’t isolate a region like Australia and try to forecast
weather there without first understanding what weather is doing in the rest of the world.
All forecast models start by predicting weather across the entire globe first. Global models are run at
relatively low resolutions and these then provide a starting point to run a regional model. Once the
global forecast is complete, meteorologists tell
the computer to focus on a region such as Australia and increase the resolution. This then allows the
computer to refine the global forecast to a high resolution and more precise forecast for the target
If computers were much more powerful then we could run global forecast models at 10 meter resolution and
that would be the end of it, we would have accurate weather predictions for every spot on earth in one
go. The reality is that computers are not yet that powerful so we have to compromise.
What happens after a forecast model is created?
Despite the best forecast models and powerful computers that run them, what comes out is essentially a
computers guess of what the weather will be. Refining this to a best guess is only achieved when
meteorologists with experience of local weather systems
review and make adjustments to the data which results in a ‘quality controlled’ forecast. You can look
at this process as follows; the global forecast is a first guess, the regional forecast a second guess
and the manual adjustment a third and best guess.
How are forecasts made for a specific location?
Once a forecast grid is available for a region, a forecast for any specific location can be made by
interpolating data from the 4 surrounding grid points. This enables forecasts to be made for any
location required, on land or at sea.
How are text forecasts made?
Text forecasts are verbal summaries of conditions that can be expected for a region. For example:
Northwest to northeasterly 10 to 15 knots tending southeast to southwesterly in the early afternoon then
tending north to northwesterly in the evening.
Southwesterly 1.5 metres, increasing to 1.5 to 2 metres during the morning.
These forecasts are made by meteorologists who look at forecast grids and try to summarise expected
outcomes for a given area for a given day. They provide a convenient way for people to understand a
forecast verbally, for example over the radio or from
one person to another.
The text forecast is for a weather region as defined by the Bureau of Meteorology. One drawback with
these forecasts is that the regions are often large and although there is variation within the region
the text forecast provides an average overall.
Significant variation can often be seen in coastal areas since marine regions extend 60nm (~110km)
offshore whereas most recreational fishing areas are close in to shore. Wind, wave and swell are often
stronger away from land and off the continental shelf so text forecasts will often say wind, wave and
swell are greater than recreational anglers may experience close in to
What Is A Seabreeze?
Sea Breezes are caused by the uneven heating of sea and land masses by solar radiation. As the sun rises
in the sky, temperatures on land get hotter but temperatures over water don’t change much. This causes
air to rise over land which sucks in air from over
the ocean and creates an air current. This air current forms a cyclic motion that picks up cool air from
the ocean and brings it inland to replace the rising hot air. Seabreezes are strongest right on the
coast line as this is where the cyclic air currents have maximum
Given the difference in temperatures increases as the day goes on, seabreezes normally pick up in the
afternoon and continue into the evening until the temperature on land has cooled.
Why do some sites try and predict the seabreeze?
When a low resolution forecast model is used in weather prediction much of the seabreeze air current is
not detectable as the forecast points are too far apart.
To compensate for this, calculations are made to try and guess what the wind would be at the waters
edge. This is often done for users like kite surfers who want to know wind speeds where they surf.
To understand this better, think back to earlier when we described how forecasts are made, now imagine we
are using the common GFS forecast model with 27km resolution that has a grid point approx. 13km out to
sea and another 13km inland.
While the model calculates wind speed at these forecast points with some accuracy, since they are far
away from the coast they do not pick up all of the cyclic air flows occurring above the waters edge.
Some sites therefor apply a calculation which attempts to predict what wind strength
would be at that point. Sites that do this typically have few locations registered as they each require
a specific set of calculations exactly tuned to a point spot on the coast.
Overall, this process is a method of interpolating a forecast where forecast grid points straddle a land
/ water boundary.
Seabreeze compensation calculations are largely unnecessary these days as high resolution forecast models
accurately calculate seabreezes natively because grid points are much closer together.
It’s only sites that use low resolution forecast models who continue to use this method. What’s more,
compensation calculations that calculate seabreezes are only intended for a particular spot and away
from that spot they are not valid.
Who produces the best forecast data for Australia?
The Australian Bureau of Meteorology (BoM) produce the best forecast data for Australia. This is what
they are there to do and they have a team of meteorologists that do just that.
Overseas agencies like the NOAA (USA) and ECMWF (Europe) produce global forecast models which cover
Australia but they are not the most accurate for Australia.
The Australian government does not spend tens of millions a year funding BoM when there is better
forecast data available for free on the internet.
Due to being poorly informed, many people in Australia still use weather sites and apps that use
Busting the Myths
Myth – Overseas agencies produce forecast data for Australia as well as the BoM.
Verdict - True. There are essentially 3 agencies that produce forecast data that covers Australia. These
Bureau of Meteorology (BoM) in Australia
National Oceanic & Atmospheric Administration (NOAA) in USA
European Center for Medium Range Weather Forecasts (ECMWF) in UK.
While there are some other agencies that produce data that covers Australia it is generally not
accessible and not commonly used by weather sites.
Myth – All weather sites get their data from BoM.
Verdict - False. BoM forecast data is relatively expensive so most sites don't use it. While all weather
sites use BoM’s network of weather stations to get current conditions they do not all get their forecast
data from BoM. In fact, most weather sites do
not use BoM forecast data at all, instead they use forecast data from the NOAA in America. The NOAA
produce a global forecast model called GFS which is available on the internet.
This data is free and provides global coverage hence it offers an attractive data source to weather
sites since they can operate a single forecast model at low cost and service the entire globe which
broadens their market. This comes at the expense of the end user who is not getting the best forecast
data for their region.
Many sites and apps like to display a banner stating they ‘Use BoM Data’ to gain credibility but in
reality, they are only using BoM observational data from weather stations and not their forecast data.
They don’t want you to know that though.
Myth – Weather sites take data from BoM then improve it with algorithms and
formulas. That’s why some have better forecasts than others.
Verdict - False. It is not possible to improve a weather forecast by simply applying an equation,
algorithm or formula. If it was then that equation would have been applied at the time the model was
Models are nothing more than the output of a series of complex calculations so adding another
calculation at the end to ‘make it more accurate’ would be easy to do if it was possible.
Although there are different forecast models available, each have a slightly different purpose, are open
source, and have been optimised by meteorologists over many years.
Differences observed in weather site forecasts are because different sites use different forecast models
as inputs, they display data differently or, most commonly, because the forecast is not at the same
point as the location shown.
This can be because the site utilises a ‘nearest neighbour’ selection method to select a forecast from a
grid or a pre-defined list rather than having an independent forecast at every location.
This essentially means when people are comparing forecasts on different sites they are not really
comparing the same location, hence there can be large differences.
BoM’s MetEye tool for example picks the closest point from a 6km grid. Some other sites that use the
GFS27 model pick the closest point a 27km grid, so the actual forecast provided by websites is often not
where users think it is. This has most impact along the coast where wind speed drops off significantly
over land. Fish Ranger uses a high resolution grid
and interpolates forecasts from surrounding grid points to prevent this problem occurring.
Myth – Global forecast models are better because they take the whole world
Verdict – False. Global forecast models are only produced to provide a starting point to run regional
forecast models and to fill gaps between continents. Each of the countries that produce global models do
not use them for weather forecasting in their own
country! Did you get that? I’ll repeat it because it’s important each of the countries that produce
global models do not use them for weather forecasting in their own country.
They instead use higher resolution regional models which are derived from the global. NOAA who produce
the global GFS model at 13km then refine it to get the NAM (North American Mesoscale) model which covers
just north America at 4km resolution. This is what the USA use for weather forecasting in their own
country. Similarly, BoM produce a global model
called ACCESS-G at 25km then refine it to get the ADFD which only covers Australia but has a resolution
of 3km or 6km (state dependent) and is much more accurate than ACC
Global forecast models are simply a by-product. They should not be used for weather prediction.
Myth –BoM website must be the most accurate because they make the data
Verdict – False. As a government agency all data produced by BoM is available to registered users; they
do not keep the best for themselves. For a fee users can access the data and use it any way required. In
actual fact, users of Fish Ranger in Victoria and Tasmania get better forecast data than BoM provide on
their own site. This is because Fish Ranger
uses individual state grid files rather than the national grid which is used to drive MetEye.
The state files for VIC and TAS have 3km resolution whereas the national file has a uniform 6km across
all states. Fish Ranger’s VIC and TAS users will therefor get more detailed forecasts than by using
MetEye (In other states the data sets are equal). Th
e difference between a 3km grid and 6km grid is a 4 fold increase in data due to their being 4 x as many
grid points covering the same area. To see the forecast as the meteorologist who created it intended,
you need to be using Fish Ranger and not MetEye.
At Fish Ranger’s insistence, at Jan 2017, BoM updated documentation to confirm this fact since it was
previously only known to some behind the scenes people and therefor doubted by the public. You can
confirm this here:
Myth – BoM forecast the wind at 3 hourly intervals, weather sites then take
that data and try to forecast the hours in between.
Verdict - False. The BoM’s ADFD dataset provides hourly wind data out to 7 days. BoM’s MetEye tool which
displays ADFD data only shows forecasts at 3 hour time steps despite the underlying data containing 1
hour time steps. Fish Ranger shows every hour as the model predicts allowing users to better see
Myth - All weather sites get their data from BoM so you are better off
going to BoM.
Verdict - False. Although BoM produce the best forecast data for Australia their website does not display
it precisely nor do they don’t show all variables users want to see such as forecast air pressure. BoM
can not be in direct competition with its customers (the sites that buy their data) so they have a
general purpose website and leave niche markets to
3rd parties. Fishermen can get the best forecast by using a site specifically designed for them like
Fish Ranger which takes BoM’s best data, consolidates the things they want to see, displays forecast
data with high precision and provides features and tools they
Myth – Averaging out all the weather sites will give me a better idea what
the weather will be than just sticking to one.
Verdict - False. Averaging weather sites that use low quality data just results in a lower confidence
forecast. More weight should be given to sites that use better forecast models. Imagine you wanted to
know how to catch a swordfish and so wanted some adv
ice on doing so. Now imagine you bumped into a group of 5 people at the pub one of who happens to be a
champion game boat skipper and the other 4 weekend warriors on the snapper. Would you take advice from
all 5 people and average it out or would you listen to the game
boat skipper and weight his advice above others? You would listen to the game boat skipper as he is the
best source of information. It’s a similar situation with weather sites.
Myth – Weather forecasts are only made where there is a weather
Verdict – False. While observations can only be made where there is a weather station forecasts can be
made anywhere. Forecast grids cover the entire country and a set distance out to sea. By looking at data
from the 4 surrounding grid points forecasts can be made for any location required, on land or sea.
Myth – If a weather site gets the weather wrong it can’t be accurate and
you should use another moving forward.
Verdict - False. Every weather model is going to get the weather wrong it’s a question of how much and
how often, you need to pick the one that’s right more often and stick to it. Think of this like an
amateur poker player coming up against a professional
poker player. Over the course of a couple of hands the amateur player may get lucky and come out on top.
If however they play for many hours the professional player will end up winning because they are a
better player. Similarly, the best forecast models will get it
wrong occasionally but they will get it right more often than poorer performing models so back the
better model and stick to it.
Myth – Satellites forecast the weather
Verdict - False. Satellites are used to measure current conditions such as sea surface temperature but
they are not used to forecast the weather. The temperatures measured by satellite are fed into forecast
models as initial conditions but they play no
What Forecast Models Cover Australia?
There are 6 commonly used forecast models that cover Australia. Four of these are for general weather and
two are for wave and swell.
Produced by BoM
ADFD stands for ‘Australian Digital Forecast Database’ and is BoM’s official and best forecast
data for Australia. It provides forecasts for weather, wave and swell. The ADFD has a resolution of 3km
in VIC and TAS and 6km in other states making i
t the highest resolution forecast data available for Australia anywhere in the world. ADFD is quality
controlled which means meteorologists in each state review the computer output and make manual
adjustments based on experience with their local weather systems. The wave
and swell forecasts are provided out to 60nm (approx 110km) from shore. ADFD is the BEST forecast data
This is a general weather model that provides wind, temperature, rain etc data. It has a
resolution of 12km out to 3 days then 25km out to 10 days. It also provides coverage in capital cities
to 4km. It is not edited by meteorologists before being released.
There are three common global models that cover Australia, these are GFS, IFS and Wavewatch III.
Global Forecast System (GFS) is a forecast model produced by the National Oceanic and Atmospheric
Administration (NOAA) of America. It is a global model which covers every part of the Earth and is the
most commonly used weather model by weather sit
es all over the world. It is available for free on the internet and is not edited by meteorologists
before being released. As computing power has increased, upgrades have enabled NOAA to increase
resolution of the GFS model. There are currently two versions in operation with resolutions of 27km and
The 13km version is better than the 27km version but many weather
sites still use the 27km version simply because they have not upgraded their systems yet.
The Integrated Forecast System (IFS) is a global model produced by the European Center for
Medium-Range Weather Forecasting (ECMWF) in England. IFS is not quality controlled and exists in 3
versions, a 55km, 18km version and a 9km version. Some
variables from the data set are free and others need to be paid for hence it is not used as much as the
The below diagram shows forecast models that cover Australia, the agencies that produce them and the
sources of data that various weather sites use for wind, wave and swell forecasts. As can be seen, many
weather sites use the NOAA GFS data model (for weather) and Wavewatch III (for wave and swell). These
are global models produced in the USA, are not the
best data for Australia and are free to access and download. Users can verify these sources for
themselves, often the ‘Help’ or ‘Terms and Conditions’ sections of the
websites, or the description page on the app store often confirm what models are used.
Fish Ranger is the only site that exclusively uses all of BoM’s forecast models and takes variables from
each to give Australian users the most accurate and comprehensive forecast possible. None of the tools
on BoM’s own site can do this.
See Appendix A confirming data sources for these sites
Notes on Diagram
BOM Interactive Weather and Wave Maps and BOM Marine Wind page do not use BOM’s best data
and instead use ACCESS, AUSWAVE and IFS data. These pages exists because BOM have a responsibility to
provide forecasts for the broader Australasian region including the high seas. Given their best wind and
wave data (ADFD) only extends 60nm out from the
coast, these pages are partially obsolete and really only exist to service areas beyond 60nm or users
needing high altitude forecasts like pilots.
Two additional sites were looked at as part of this comparison – Swellnet and Wind Junky, however they do
not clearly reveal their data sources so they have not been included in the diagram.
- Swellnet does have a WAMS page that shows weather maps. Prior to AUSWAVE coming online in
2010, BOM had a wave model called WAM (Australian Wave Model). Based on the name, Swellnet may or may
not be continuing that same model for its wind,
wave and swell forecasts. You can see BOM’s historical forecasts for WAM here: http://www.bom.gov.au/climate/how/newproducts/IDCdwamgrids.shtml
- Wind Junky says its data is from BOM but it does not say what model nor does it display the required
attributions which are a requirement of using BOM data. Also, it doesn’t actually show where the
forecast is being taken, on water or on land.
Willyweather use the ADFD data set however its unknown if they use the national or state files.
Importantly, their forecasts including wind are land based (apart from a few exceptions) so do not
represent conditions on the water. They also do not provide marine text forecasts and they do not use
BoM’s ADFD-Marine data for swell forecasts, instead opting for the
free American alternative, Wavewatch III.
Observations are measurements of weather taken by weather stations. There are 870+ weather stations
throughout Australia and they are operated by the Bureau of Meteorology. Forecasts are predictions of
weather in future made by computers that run mathematical models. The Bureau of Meteorology produce the
best forecast data for Australia but most weather sites
do not use it. Instead they use the GFS forecast model produced by NOAA in America which covers the
entire world and is freely available on the internet.
Weather sites use GFS data as it enables them to operate a single forecast model at low cost and service
the entire globe which broadens their market. This comes at the expense of the end user who is not
getting the best data for their region. BOM’s best data for Australia is called the Australian Digital
Forecast Database (ADFD) which has a resolution of
3km in VIC and TAS and 6km in other states. It is manually adjusted by meteorologists with knowledge of
local weather systems before being released. Due to technical limitations with BOM’s own site, MetEye
does not show ADFD data in its full detail. Fish Ranger reveals
full details of the ADFD data set making Fish Ranger forecasts more precise than those from MetEye.
Along the way we busted many weather site myths and discovered:
Many weather sites do not get their forecast data from BOM
Weather forecasts can not be made more accurate by applying an equation or algorithm over the top of forecast model data.
Averaging multiple weather sites that use low quality data just results in a lower confidence forecast.
Applying calculations to determine seabreeze at the waters edge are not required when modern high resolution forecast models are used.
Weather forecasts can be made anywhere, not just where there is a weather station
Satellites do not forecast the weather
BOM’s ADFD data forecasts wind at hourly intervals however MetEye only shows every third hour limiting users’ ability to see approaching changes.
MetEye does not use BOM’s best forecast data in VIC and TAS. In other states it does.
So What Does All This Mean?
Although weather forecasting is not a precise science and forecasts are often wrong, users can be assured
that by using Fish Ranger they are getting the best forecasts they can possibly get. Fish Ranger takes
BoM’s best data from a range of products and consolidates things fishermen want to see thereby taking
the guess work and hard work out of it. Forecasts
are taken where people actually fish including over open water where wind is often stronger than land.
Easy to read charts reveal every aspect of detail as the meteorologist that created the data intended.
Real Time overlays make it easy to see how weather is tracking
compared to forecast. Fish Ranger is the go to weather site for anyone planning a trip on the water.
Appendix A – Links to weather sites confirming their data sources
Fish Ranger exclusively use BOM’s forecast data to provide forecasts.
Although ADFD is the most precise model it doesn’t include all variables of interest
to fishermen so some variables like air pressure are taken from ACCESS and Total Wave period
taken from AUSWAVE.
Buoyweather use GFS and Wavewatch models for Australian weather forecasts. They
use the NAM model (North American Mesoscale) for USA but the rest of the world get GFS.
The NAM model has higher resolution than GFS so Buoyw
eather are providing good forecasts to the USA and average to everyone else. When they say
they are providing the highest resolution forecast, they should clarify that is only the USA
that get that ☺
Seabreeze use GFS data to create their wind and wave charts. They credit NOAA
in their attributions and their charts are updated 4 times per day. BoM don’t produce
any 7 day forecasts which are updated 4 times per day.
The BOM Marine Wind Page uses ACCESS and ECMWF IFS forecasts.
This is not their best data. The bottom of the ‘About Forecast Wind Page’ confirms this
and advises users to use MetEye. This page really only exists to service areas
beyond 60nm from shore.