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Weather Forecasters

Yesterday, the ABC News website weather report was showing a 70% chance for between 0 and 3 mm of rain in Mt Sheridan.

When our scientifically calibrated Peters Ice Cream bucket was full with some 125mm of rain, I placed another plastic pot on the path to the pool last night, and I measured some 150mm init before I emptied both of them this afternoon.

So a mere 225mm in 24 hours, or what the locals call a light shower.

However, there is now a dire warning on the ABC News website regarding the latest forecast from BOM.

So between the ABC News website and the BOM, we have gone from 0 to 3mm yesterday to 'The Great Deluge" after the event.

My sister says that weather forecasters were only ever created to try to make financial forecasters look good.


Your sister needs to review the improvements in accuracy of the forecasts over the past decades. Sometimes the forecast is right on, just a 100km or so offset as wind patterns change rapidly or the models are off a bit.

The recent forecasts round Melbourne have been very good, including precipitation. Climate models are even better.

Somewhat of a layman’s tutorial…

Disclaimer: Spent a while in the business.


As I said to my sister, and many other people, weather forecasting must be the only official job where you can get it wrong everyday and never get fired.

Fortune tellers, clairvoyants, charlatans, witch doctors, and snake oil sales people are not covered by such requirements and so are exempt.

When the forecast for my suburb shows 0 to 3mm yesterday morning and we get some 225mm in 24 hours?

And the BOM flood warning from Cooktown to Ingham.

Meanwhile, back on the ABC News website.

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But they don’t, most of the time in most places they are mostly right out to about three days. This may be inconvenient for your story but the only way to test your proposition is statistically which you do not do.

One reason that it is popular to bag weather forecasts is confirmation bias. People expect forecasts to fail so every time they do they remember it vividly and every time the forecaster succeeds they don’t notice. So their recollection is filled with failure; QED.

Weather is chaotic (in the mathematical sense), that is small variations produce unexpected outcomes which means that:

  • forecasting will never be 100% right,
  • the longer into the future you look the chance of making any sense declines.

Chaos: When the present determines the future, but the approximate present does not approximately determine the future.

Chaotic behavior exists in many natural systems, including fluid flow, heartbeat irregularities, weather and climate.


… it also seems consistent that ‘forecast deniers’ will deduce that anything less than 100% right, is simply wrong, not - for example - 98% right.


Another thing people fail to recognise is that although a forecast may be for your suburb, its actually for the area immediately around whichever station they use, too. In my case, thats Nobbys Signal Station and its some 15km away. The summer temps they advertise for my suburb are never accurate, because they are on the ocean, and I am here on the west side of a hill with no western sun protection. Likewise, the rain can be pelting down here, with none at Nobbys, or vice versa. This is why I have a Netatmo weather station, (the most basic version) and I also plan to get a barometer. Wish I had kept my Dad’s.


Doesn’t yours have a barometer?

I have been tempted to buy my own AWS but I am 2 blocks from a high school that has a Davis system online. The weather 2 blocks away is close enough for me :wink:

The BOM also has a facility that is not widely known, implemented here in conjunction with the UK Metoffice.


@Fred123, do you look at this beta facility at the BOM?


Nope, its pretty basic and has no forecasting capacity. The baaromeetric pressure here is just for “now”. Cant tell whats coming, really, unless you refresh every few minutes to see if it changes. Any forecast in the app is gleaned from elsewhere (usually the BOM and Nobbys)

Here’s a screenie. I kinda like the old style barometers though. Taptaptap on the glass to see which way the dial will move.

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Isn’t this your barometric pressure or does the software import that metric? Or is this not your own system?


The high school system software is Very Old. Davis wants more than $300 for an update. It runs on a Windows98 PC and apparently isn’t amenable to newer windows systems. Thus the comparative crudeness…

They do get the occasional spider web problems but it has generally been very reliable, save for our local power grid being dodgy.


I edited my previous post for clarity over that pressur reading. Its just a now thing.

The sea breeze effect is but one of many reasons that what you get in your back yard may not match the BOM predictions for a district. In some cases a few kilometres makes a noticeable difference.

Part of the problem is the level of details that can be calculated by the BOM is limited but also the level that there is time to report in the media. We all tend to suffer due to generalisations. For those who have reason to think their location is not typical of the report of the region there is a BOM product that may help you out called Meteye. It allows you to zoom in on your locality, using the Hunter as an example there is a huge difference between Newcastle CBD and Scone. We all knew that but not necessarily what you can do about it or what you can do if you are not in a named town that gets its own forecast.


Which is why we get our own weather stations. I would have got a Davis system if I could have afforded it. But they are very expensive. There are a few on ebay (not Davis) which are fairly well regarded, and of reasonable price. When the temp at Nobbys is 30ºC out here at my back door, it can be over 40, just because of my location and lack of protection from the sun on that side of the house, and itss exactly why I ended up going with Netatmo.

Isn’t the reliability of the weather dependant on who is presenting the nightly forecast?

I’m a firm believer in trusting the weather expert at the end of the nightly news. SBS in particular. That it can turn out different the next day. Well, that’s weather isn’t it! :wink:

Aside from looking out the window, the BOM radar resolves most needs. We can have 150mm rain recorded here by the BOM and the town 5km up or down the road 10-20mm. There is a wonderful network of rainfall and river height recording stations accessible on the BOM. Very useful if you are have webbed feet, or live in or near a flood zone.

There is also a BOM AWS less than 10km down the road that’s useful for more mundane stuff.


I am not aware of any of the personal weather stations that forecast. Forecasting is a pretty intensive process. For example the BOM has a state of the art Cray XC50 capable of 4 petaFLOPS upgrade being installed, if not already installed. Those ‘weather stations’ that ‘suggest’ rain is coming or whatever are only sledge hammer approaches based on barometric pressure, as simple as it gets.


Meteye can be frustrating to use and my semi-educated guess is the facility I posted for @Fred123 a few posts earlier is driven by meteye data. Far more user friendly and shows most of the detail, although not quite all.


Air pressure can provide some information on the likely weather in most areas.

A higher pressure (atmosphere is circulating downwards) indicates that a high is passing and these usually provide stable weather conditions and low likelihood of rain. Note: Coast areas can be different as moist onshore winds influenced by topography can trigger showers irrespective of air pressure.

A lower pressure usually means less stable atmospheric conditions (atmosphere is circulating upwards) as the air in the region is moving upwards and this can cause condensation and subsequent precipitation in the cooler upper atmosphere.

A rising pressure trend can mean moving towards stable weather conditions ahd a falling pressure trend potentially less stable conditions are possible.

There are many possibles and maybes, aa weather is a chaotic system with many variables and influences. …which makes accurate forecasting possible in a country like Australia very challenging. As a result forecasts are exactly that.

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Sounds like it is time to upgrade to free software, as the Weather Station software that comes with Davis stations is less than ideal. I’ve used Cumulus with mine for many years.
It does show a forecast, but while it may be of some use in northern Scotland (developer lives on Sanday in the Orkney Islands), it has very little in common with reality for inland NSW.


Noted by any who have been on the receiving end of storm events involving super cells.
The conditions leading up to them are known. But whether weather forecasts can predict if the final triggers will arise or more importantly to the nearest 500m when and where?

By the time the barometer has dropped that extra few pascals the sledge hammer rain on the roof sweeping in across the verandahs and horizontal bending of the paper barks is just as effective.

Should we be critical of our forecasts or …
The BOM for some time has been under funding pressure including Government driven efficiency dividends. Arguably it has also come under pressure from some for its role in advising on long term climate trends, seen to be supporting climate change science.


There is no argument. It happened.

edit: Getting a little off topic, but more substantiation to how scientists get crippled is when politics trumps science as well as national preparedness…