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UK Weather In May

June 5, 2012

By Paul Homewood




Although most of the month was cool and damp, the heatwave in the final week lifted temperatures back just above average. Mean temperatures averaging 10.5C made May an unremarkable 36th warmest since 1910 and compared with the 1971-2000 average of 10.1C.

As for rainfall, totals of 66.8mm, against an average of 66.2mm, and a ranking of 50th wettest since 1910 made the month as typical as they come.






So how does this leave the Met Office forecast made at the end of March for April/May/June? Let us remember what they predicted then.


The UK-average temperature forecast for spring (April-May-June) shows a range of possible outcomes that are warmer than the range observed between 1971 and 2000 (our standard climatological reference period), but quite similar to the last decade. For April the forecast also favours temperatures being warmer than the 1971-2000 reference period; however the chances of a repeat of last April, which was the warmest in over 100 years, look very low. The probability that mean UK temperature for April-May-June will fall into the coldest of our five categories is less than 5%, whilst the probability that it will fall into the warmest of our five categories is 55-60% (the 1971-2000 climatological probability for each of these categories is 20%).

……..Indeed the forecast curve lies about 1° Celsius above the climatological curve (black). In a 3-month mean this constitutes a substantial change.

So far, mean temperatures for April/May average out at 8.4C this year, compared to the 1971-2000 baseline of 8.6C. Unless we get a flaming June, which there is no sign of at the moment, it looks like another monumental Met Office fail.

What about rain? The Met hedged their bets a bit more on this one.

The forecast for average UK rainfall slightly favours drier than average conditions for April/May/June as a whole, and also slightly favours April being the driest of the 3 months. With this forecast, the water resources situation in southern, eastern and central England is likely to deteriorate further during the April/May/June period. The probability that UK precipitation for April/May/June will fall into the driest of our five categories is 20-25% whilst the probability that it will fall into the wettest of our five categories is 10-15% (the 1971/2000 climatological probability for each of these categories is 20%).

Actual rainfall in the last 2 months has been 193.3mm, well above the average of 135.8mm. Given that the 1971-2000 average for all 3 months is only 208.4mm, there is absolutely no chance the 3 month totals will come out drier than normal. The Met Office will no doubt claim they did forecast a possibility of this, but of what possible use are such “heads I win, tails you lose” forecasts?

Perhaps chairman Robert Napier (ex WWF) should take the useless Julia Slingo with him, when he does the honourable thing.


The full 3 monthly outlooks are here and here.



According to the Met Office Science Strategy 2010-2015, written by Slingo,  one of four major challenges is “Monthly to Decadal Prediction in a changing climate”. The strategy goes on to comment:-

Monthly to decadal prediction is still in its infancy and the potential predictability in the climate system for these timescales is largely unknown and probably underestimated because of model shortcomings.

While it’s nice to hear her admit the monthly forecasts are a waste of time, I don’t recall Slingo or her colleagues warning us all to take their century long forecasts with a pinch of salt.

  1. June 5, 2012 7:09 pm

    I’ve asked the Met when they are going to change the standard climatological reference period from 1970 – 2000 to 1980-2010. The answer is fuzzy. It couldn’t be because starting in 1980 would take out the colder temperatures of the 1970’s, resulting in a higher reference point and therefore making temperature drops over the last 3 or 4 years more noticeable, could it?


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