Cast ne'er a clout till May's out

I mentioned some time ago that Piers Corbyn had been up to his old tricks with an apocalyptic prediction of doom for the coldest May ever in the UK, right in time for our recent trip there.

May is long since out, and it's time to get clouting. May turned out to be slightly warmer than average. I wonder who actually pays for his "forecasts"?

Barbecue summer - the sequel!

Oh, I suppose I shouldn't poke fun. Having got their fingers burnt last year - or perhaps I should say, having had their parade thoroughly rained on - the UK Met Office is declining to offer public forecasts, but is still doing "experimental" research on seasonal prediction and has obviously given a nod and a wink to the author of this Times article.

Of course we all know how the last "barbecue summer" turned out:

“Well, let’s put it this way. I’ve put my barbecue in the shed,” Dave says. “I don’t want it to get any rustier.”

I'm going to be in the UK for a chunk of the summer, so I hope they have got it right this time.

I am reminded that earlier this year, the BBC put out its weather contract to tender. Rumour has it that the esteemed Piers Corbyn, in a change of focus from his current work in volcano and earthquake prediction (no I'm not joking on that bit), is putting in a strong bid.

By popular demand...

My reader seems to think it's time I said something about our friend Piers:

(pic from my hit counter).

The context is obviously the embarassing bust of the UKMO forecast for a hot summer. My sympathy for them is in rather short supply, given the ridiculous way in which they have over-hyped the "danger" posed by the possibility of some tolerably pleasant weather over recent years. As I said at the time, even if it did turn out warm, the impact on human health was hardly going to come close to their hyperbolic suggestions (yeah yeah, you can try to pretend it's all the fault of the press if you like, but I don't see anyone trying to correct them).

I can't blame Corbyn for crowing about it, not that I actually think his opinion is worth anything. However, it does highlight the difficulty that numerical models have with handling the subtle shifts in weather patterns that can have a strong influence on the UK's climate. Coming hot on the heels of some thoughtful (and thoughtless :-) ) criticism of the recent UKCP predictions I suspect there may be some rather long faces in Exeter...

Corbynwatch 2008: The Verdict

I seem to have missed out several months of Corbynwatch. In fact my last post appears to have been early Sept, concerning his August forecast. To be honest I was getting a bit bored by then, and was also suspicious of his methodology of only sending out his forecasts a few days into the month, and sometimes not at all.

But he did send out the October forecast, and turned out to get it right overall (amusingly, he predicted a cold first half and milder second half, whereas reality produced the exact opposite - nevertheless, on the monthly figures his overall estimate of -0.2 to -1.2C captured reality's -0.6C, and the very average rainfall was also in the middle of his range). So that got his score up to a reasonable 10 out of 16. November, on the other hand, was a complete bust. His forecast was for very cold (at least -1C compared to the long-term mean) and wet (130-200% of normal) month, but it turned out slightly mild (+0.1C) and slightly dry (90%).

I never saw a December forecast, so his final score for the year score sticks on 10 out of 18. (with only 9 forecasts available). If his accuracy really was the claimed 80%, such a poor result would have a less than 2% probability of occurring.

While he didn't issue a public prediction about the December mean temperature, he did say:

Piers and colleagues have placed bets of about £1,000 with William Hill and Coral for snow at various locations on Christmas Day and stand to win many thousands if they are correct.

Piers whose record of weather bets is second to none* said: "We have just made a breakthrough in our 'Solar Weather technique of long range forecasting - called SWT25 - and are 75% sure there will be snow in many but not all locations offered by boookies this Xmas, and we have a fair idea of where the best bets are likely to be".

This £1,000 was of course lost.

He has also predicted that 2009 will be outside the top 5 years, in contradiction of the UKMO prediction. I don't have any plans to follow his forecasts in detail though - especially as there is no sign of the January prediction.

Corbyn again

The August data are in, and once again it is 2 out of 2 for Piers! The daily max temperature was 1.2C below average, covered by his range of 0.3 - 1.3C colder than average, and rainfall at 165% was also inside his range of 125%-175%.

So he's up to 8 out of 14, which means the p-value is still below 5%, but it is heading in the right direction. There is no sign of the September forecast yet. The August one only appeared on the 8th, by which time it was already well set to be very a wet month with cold days, but of course he claims that this forecast was really made some time previously...

Another good month for Corbyn

July was a good month for Corbyn's monthly forecast - the rainfall of 167% was in his predicted range of 160-250%, and the mean daily max (anomaly) of -0.8C was also in his range of -1 to -0.2 (data here). The various specifics were largely wrong but I can't go cherry-picking what to evaluate after the event. [I did initially say I would use mean, not max, temp but that was before being pointed to the max data on Philip Eden's broken site.]

So now he is up to 6 correct forecasts out of 12 so far this year (temp and precip for 6 months, June being curiously absent). That still represents a p-value of less than 2% based on his claimed 80% accuracy. That is, if his forecasts really had a long-run probability of 80% of validating, then the probability of getting 6 or fewer correct out of 12 is under 2%. On the other hand, it is better than chance, given that his ranges generally cover less than 50% of a reasonable climatological range. (That doesn't mean much, given that he only publishes the forecast a day or two into the month. The very heavy rain at the start of July was easily predicted by everyone at that point. Also, there is the question as to why June's forecast was not released...but there is little point in speculating on that point.)

Corbyn on July

For some reason I never saw a copy of Piers Corbyn's June forecast, so I can't evaluate that. He did breathlessly announce on the 26th (Thursday): Our long range forecast for deluges and floods between 29th June and 2nd July still stands - so Glastonbury and Wimbledon watch out! However the only report I saw about Glastonbury at that time said it was pretty dry, even sunny by Sunday, and the drizzle at Wimbledon on the 2nd certainly wasn't enough to save Andy Murray. With typical chutzpah, he is still claiming he got this right - can anyone point to any "exceptional torrential downpours" in this interval? (I'm aware of some fairly heavy rain on the 27th, I even got to enjoy it as I was in Sheffield at the time.)

Anyway, on with July. It's going to be extremely wet ("probably one of the three wettest Julys on record") with a rainfall of 160-250% of the average over England and Wales. Just to be difficult, his temperature prediction is for the daily max rather than mean as previously. This is predicted to be 0.2-1C below mean, and he also says that the mins will probably not be below normal. I reckon I can therefore reasonably assign a range of about -0.5C to +0.2C for the means (for comparison with data). If the mean is outside this range, then it is hard to see the max being in Corbyn's prediction. I think this is probably generous to him, but will be happy to hear alternative suggestions.

As well as the UK weather, he has thrown in some typhoon predictions for free. Apparently there's a 60% chance of Japan taking a hit in the first half of the month or so. No sign of them so far and it has been particularly cold here this year, although I don't know what the sea surface temperature is looking like in the formation zone.

I've been away, BTW, for those who were wondering if I'd given up entirely.

Corbyn's May forecast

After last month's success, I'm relieved to say that things are back to normal for May, so my hat is safe from the frying pan. Remember, Corbyn forecast a cool month (0.5 to 1C below normal) with average rainfall (90-115%). Well, it turned out rather warm at 13.6C (here and here), which is more than 2C above the normal for May (about 2 standard deviations), and the rain was also clearly above his range (currently 128% at Philip Eden's site, although there is one more day to update there, which cannot bring it into the forecast range now updated to 124% for the full month). The temperature looks like it should be among the 10 warmest on record (and it could possibly be the warmest May for 160 years), although we will have to wait for the official figures to be sure.

So now Corbyn is down to a 40% success rate for the year so far (4 hits from 10 forecasts). Even if he gets every remaining month for the rest of the year perfect for temperature and rainfall, he cannot climb back up to his claimed 80% success rate.

Woohoo! Corbyn nails it!

Well, he got it right one month in a row. Honestly, I'm impressed. I'll be even more impressed if he gets it right for the next few months, though. For the record, April was close to average temperature and just above average rainfall, both comfortably within his predicted ranges. So now his score is up to 4 out of 8 for the year, which is still not close to his claimed 80% success rate, but slightly better than it was last month. Since it is late on a Friday night, I'll leave the binomial probability thing as an exercise for my readers :-)

Corbyn thinks that May should be about average for rain (90-115% of normal) but rather chilly, at 0.5 - 1C below average for the month. There aren't any exciting weather events forecast (you can't go far wrong with "variable: some showers" in May).

Corbyn's April forecast

Looks like the fun is set to continue for a little while longer, cos I've got Corbyn's April forecast. He thinks that April will be cool and rainy. This month he has unhelpfully split the Central England Temperature region into no fewer than three sections, so I'll make an estimate of the average: the SE chunk is predicted to be from -0.5 to +0.5C, the western chunk is -1 to 0C and a northern wedge is -0.8 to 0.2C - all values compared to the 1961-90 mean which is 7.89C for the CET series. So I'll take the overall average of that to be -0.75 to +0.25C and anything in that range (7.14 - 8.14C) will be a win for him. Rainfall is a little simpler, his forecast is 110-140% for the west and 95-130% for the east and north, so I'll allow 100-135% to count as a win.

As for notable events, the Grand National (5th) will be warm and dry, and the London Marathon (13th) will be positively warm or even hot. The Met Office disagrees on both counts (well they suggest the LM may be OK-ish), but what do they know?

March Corbynwatch

A quick update on the March results: Corbyn gets a fail on the temperature (he predicted colder than normal, it was warmer according to here and here - note that "normal" in his terms is the 1961-90 mean, which was 5.67C) but a success on the rain - he said upwards of 130% of normal, and Philip Eden says we had 135% (I'm simplifying Corbyn's forecast here a bit, since I don't have precise regional data). As before, I'm ignoring the sunshine on the basis that this is essentially the converse of the rainfall forecast: for the record, he was actually wrong.

So a second successive 50% result means that the scores on the doors have "improved" to 2 out of 6 for the first 3 months of the year. However, despite the higher overall success rate, the failure of his method is actually marginally more clear-cut now, since the gap between the actual success rate and the claimed 80% forecast accuracy is more apparent:

Successes (out of 6)	6 or 5	4 or 3	2 or less
Probability	66%	33%	2%

(Yes there's a rounding error there, all three values are actually a little lower than quoted.)

I hope someone will supply April's forecast. If he gets the next 7 months spot-on (temp and precip) he'll be up to the 80% rate that he claims, and I will eat my hat, video the event and post it on Youtube.

Corbyn on March

I've got hold of Piers Corbyn's forecast for March. He predicts that it will be cold, very wet and slightly cloudier than average. According to Philip Eden, he's wrong on all counts at the moment.

The (in?)famous Wheeler paper specifically focussed on gales, and there was of course a severe storm a few days ago across much of the UK. So it's interesting to see what Piers predicted for that interval:

Cold with fog and frost. Some wintry showers. Wind: light/mod.

The Calcutta Cup match was supposed to be "Prob dry. 10% risk of shower."

Oh well, there's always next week to look forward to, for which he forecasts.

18-21 Mar (85%) Very wet & windy, thunder and local floods. Gales.