Piers Corbyn WeatherAction accuracy and analysis

I carried out a 6-month analysis of the weather forecasts of Piers Corbyn, a London-based long-range weather forecaster. I don't believe anyone has done this before.

My conclusion is that there is definitely something to his ability to make weather forecasts weeks ahead that beat anything standard meteorologists can do.

For the periods analysed I would say that he was typically around 70% accurate, but what was particularly impressive was his ability to forecast 2 storms over the UK in September and November 2012 with perfect accuracy from over a month ahead.

It would be beyond all reasonable probability that this could be attributed to chance.

His predictions of the general movement of the Jet Stream and air pressure patterns were in the region of 75%. Sometimes this general weather scenario failed to translate into an accurate weather forecast for specific areas, because his forecasts for the position of areas of high and low pressure were slightly different from his forecasts resulting in weather that was markedly different.

Nevertheless, his forecasts are frequently accurate, sometimes impressively so. Piers Corbyn himself claims an accuracy of "6 out of 8" for the 8 or so periods he splits each month into. For the months analysed I believe he was close to this figure.

I think that with the aid of a super-computer and co-operation from the established meteorological community his methods of forecasting could lead to a major advance in medium and long-range forecasting.

His climate change scepticism means scientists will not go near him right now but given his forecasting success he deserves to be taken seriously.

In the 6-month period I believe my analysis largely vindicates his own claims about his weather forecasting success, with some reservations.

Irrespective of the overall success rate there have been occasions when the forecasts have been remarkably successful in predicting unusual weather patterns. This demonstrates that there is a significant solar/lunar weather influence that is not yet understood.

6-Month Analysis of Weatheraction forecasts

May-October 2012

I have undertaken a six-month long analysis of the accuracy of the weather forecasts issued by Piers Corbyn though his company Weatheraction.

General Conclusion:

On the basis of the 6-months subject to analysis I conclude a forecast accuracy of approximately 70% (if the criteria outlined below are accepted), with a slightly higher success rate of approximately 75% in forecasting the general air pressure scenario.

Sometimes the general pressure forecast is not necessarily translated into an accurate weather forecast. This mismatch is usually due to the pressure scenarios that occur being slightly different from forecast, resulting in the weather being markedly different from forecast. On some occasions he got the pressure scenario correct but still forecast the wrong weather, which may suggest a lack of meteorological expertise which could be rectified by working with professionals in the field.

Looking at certain elements of Corbyn’s predictions, such as the storms around the 23rd/24th September and again around 22nd/24th November which were forecast in detail very successfully, it is evident that there is a forecasting ability significantly greater than by chance. It would be difficult to attribute two highly accurate storm forecasts to the day from 30 days ahead to mere chance or luck. The odds of forecasting these two events by chance are extremely slim indeed, not to mention forecasting the nature of the pressure events that led to them being very accurate as well.

This conclusion is a general observation I picked up later on about the Weatheraction forecasting effectiveness that was not drawn from the spreadsheet analysis specifically (which only goes up to October) which focussed on actual weather with only occasional comments about the wider pressure scenarios.

Summary points:

1) Piers Corbyn’s “SLAT” technique achieves significant success at making general pressure forecasts and movements in the jet stream.

2) His success at detailed weather forecasting is in the region of 70-75% though this is a highly subjective figure based on what constitutes a success. I have worked on the basis that my blue and green ratings are classed as successes. Analysis could be much stricter or more lenient but given the statements by Corbyn that his forecasting is only a guide to the most likely outcome I have chosen a level of success based on his forecasts being approximate guides to likely weather.

3) There is a mismatch between his often successful pressure forecasts and his less successful detailed weather forecasts. This is usually because the pressure and jet stream forecasts are slightly incorrect which in turn means the weather is significantly different than forecast. For example, the southerly shift of the jet stream around the 21st August was forecast correctly but this change in the jet stream didn’t produce the change in weather predicted for the British Isles. Likewise, a forecast for the final period of October predicted that an area of low pressure in the North Sea would bring a northerly wind across Britain, and hence cold weather; the area of low pressure materialised as predicted but it was a couple of hundred miles to the west and, as a result, brought a southerly wind instead and milder weather.

4) It is possible that this mismatch could, at times, be due to a lack of expertise in meteorology which means that his pressure forecasts are not translated into weather forecasts correctly. Working with the Met Office or other professional meteorologists might improve this.

5) Sometimes elements of weather emerge a couple of days either side of the forecasts, though Corbyn acknowledges this.

Monthly Summary


Corbyn predicted it would be the ‘Coldest May for 100 Years’. Taken literally this claim was wrong, but it would be fair to say it was 75% correct, because the first 3 weeks of May were much colder than average. The last week had sunny and warmer weather which Corbyn later admitted had no precedent in his historical solar/weather pattern records.


Corbyn’s prediction of a very wet month turned out to be spot on. Some detail was off, but a very impressive monthly forecast overall.


July was predicted to be similar to July. It was a good monthly prediction although one period turned out much drier and sunnier than forecast.


The general prediction was of a similar 20 days to the previous 2 months, and that summer would begin around the 20th due to the Jet Stream moving very far south. The jet stream did move south when predicted, but not quite as far as Corbyn expected and the weather continued to be wet and overcast. The Jet Stream forecast deserves, say, an 8 out of 10, but his actual forecast 0 out of 10!


A couple of periods were forecasted incorrectly, although the intense low pressure area that caused stormy weather across the British Isles on the 22nd/23rd September was predicted brilliantly. Corbyn’s description that the low pressure area would “torpedo” in from the South West was very accurate. It formed in the middle of the Atlantic and remained a concentrated area of Low Pressure as it moved towards the British Isles.

March 2014 edit: This type of low pressure event has only happened once in the 3 years I have now been following the weather closely so this is near certain proof of Corbyn's SLAT method - unless one is prepared to accept it as a lucky guess of lottery winning proportion.


The month began according to Corbyn’s predictions. There was a prediction of “Indian Summer” weather around the 21st-25th, following by a cold snap around the 29th. This period is very revealing about my overall conclusions. The ‘Indian Summer’ weather did not materialise and the week was dreary and overcast everywhere. However, the pressure situation predicted for this period was correct and it is possible that Corbyn, at this instance, lacked the metrological expertise to translate his pressure forecast into an accurate weather forecast. The Met Office might have been able to take the general pressure forecast and conclude, “this will lead to overcast, not sunny, weather”.

The elements of the weather in the last three periods were all present, though not at the times predicted. The cold spell happened a couple of days earlier than forecast, as did a “sausage high” pressure area that was predicted. I have stated on the spreadsheet that the yellow ratings for these periods could be viewed as being too harsh given that Corbyn himself states that the weather may occur within a day or two of the scenarios forecasts.

As mentioned above, in the final period Corbyn predicted that an area of low pressure in the North Sea would bring a northerly wind across Britain. The area of low pressure materialised as predicted but it was a couple of hundred miles to the west and, as a result, brought a southerly wind instead with milder weather.

This is a good example of my conclusion that Corbyn is good at predicting general pressure and jet stream scenarios but does not always forecast this accurately enough to translate into an accurate weather forecast for regions of the British Isles. Perhaps it may not be possible to predict the weather to a high degree of accuracy over such as small an area as the British Isles, but with the computing power and knowledge of the Met Office, perhaps significant improvements could be made.

Later months:

November – the storm forecast for the 22nd-24th was very accurate

January 2013 – the general pattern of snowfall and temperature was accurate

Feb-June 2013 – based on the same criteria an approximate accuracy of 3/4 was observed

Personal Opinions
The Met Office should be prepared to work with him, and not regard his climate change views as a barrier to this. Simply ignoring Corbyn because of his radical views on the traditional theory of global warming is wrong. His success in forecasting pressure areas and the jet stream would suggest he is correct that the sun plays a more significant part in climate and weather patterns than hitherto believed. Whilst Corbyn may or may not be wrong about CO2, it is possible that the influence of CO2 is less than previous thought simply because the impact of the sun is far greater than thought. Given Corbyn’s greater-than-chance success in the 6-month period, and his highly impressive specific forecasts (such as the storm, 22nd Sep), his theories and methods deserve attention from the scientific community.

Corbyn should be allowed to debate his ideas on the impact of CO2 in a public forum with climate change scientists in order to ‘clear the air’ and remove the scepticism that many in the business have with Corbyn. If he is wrong then it ought to be easy to demonstrate by climate change experts.

He should then present his ideas to professional meteorologists and work with them to aid their medium and long-range forecasting.

Corbyn should publish his theories and submit them to peer review. Further research, possibly taking years, could then be undertaken, and he could be involved with it.

To those who believe Piers Corbyn should simply be dismissed or ignored, I wish to point out that he has the ear of many in the current government, including Boris Johnson, who may be a future Tory leader and even Prime Minister. If the PM was taking advice from an astrologer then this would be taken very seriously. Simply telling Boris Johnson that Piers is wrong is clearly not enough and I would urge the scientific community to critically analyse Corbyn’s work, as I have done, in order to (as they believe they would) discredit him.

Alternatively, they may conclude that there really is a genuine long-range weather forecasting ability and that the methods employed by Piers Corbyn demand further attention.

Questions about the SLAT technique

To what extent are his forecasting inaccuracies due to the sun not acting as predicted (which, for example, may have led to the ‘sausage high’ being a few days earlier)?
How accurately can the sun be predicted?

Or is it that Corbyn’s sun-to-weather calculations lack the expertise of a professional meteorologist, and, with help, could be more accurate?

In other words: if the forecast for solar activity is correct, does this always produce an accurate weather forecast? Or are the inaccuracies due to a failure to translate the solar pattern into the weather pattern?

Does Corbyn understand how the sun affects the weather, or has he simply identified that it does from historical records?

Could an archivist or statistician with access to Corbyn’s data use the SLAT technique, or does it require an actual knowledge of physics?

Could it one day work without reference to the historical record by identifying precisely how the sun and weather interact?

How long and what type of research would be needed to achieve this?
With the multi-million pound resources of the Met Office how accurate could SLAT become?