The Bureau of Meteorology installed a multi-gazillion dollar supercomputer a year or two back, with the aim of improving the accuracy of weather forecasts.
How accurate are they? Well over about a week, I compared forecasts (including up to a week ahead of the day) against the actual weather reported the next day. I was seeking to answer these key questions:
- Do they alter forecasts markedly as the day gets closer?
- Are the all-important forecasts the day before actually accurate, so you know if you can leave the house without taking a brolly?
- Is this kind of detail so deadly boring and sleep-inducing as I’m suddenly suspecting it might be?
|Day||Forecast days in advance||Actual weather|
|Mon 9th May||Mainly fine||Mainly fine||Mainly fine||Fog then fine, 18||Fog then fine, 18||Fog then fine, 18||Fog then fine, 18||Fine, 17.3|
|Tue 10th May||Mainly fine||Mainly fine||Mainly fine||Fine, 18||Fine, 18||Fine, 18||Fine, 18||Fine, 18.5|
|Wed 11th May||Mainly fine||Mainly fine||?||Shower or two, 17||Early shower, 17||Early shower, 17||Shower or two, 17||Fine, 19.1|
|Thu 12th May||Mainly fine||?||Mostly fine||Fine, 18||Fine, 18||Fine, 18||Fine, 18||Fine, 16.7|
|Fri 13th May||?||Mostly fine||Mostly fine||Mostly fine||Mostly fine||Mostly fine||Fine, 18||Fine, 18.3|
|Sat 14th May||Mostly fine||Mostly fine||Mostly fine||Mostly fine||Mostly fine||Fog then fine, 19||Fog then fine, 19||Fine, 21.8|
|Sun 15th May||Mostly fine||Mostly fine||Fine, cool||Mostly fine||Mostly fine, 17||Mostly fine, 17||Fine, 17||Fine, 19.3|
Notes: ? — oddly, on Saturday 7th of May, they weren’t brave enough to forecast more than 4 days ahead. And don’t ask me what the difference between “Mostly fine” and “Mainly fine” is.
If you’ve got nothing better to do: See all the figures (XLS, 19.5Kb)
In conclusion, it seems they’re pretty accurate, with temperatures usually within a couple of degrees of that forecast the previous day. Even the advance forecasts don’t change a great deal before the day. Mind you, we did have a run of fine autumn weather. But still, I’m suitably impressed.