Will summer be a washout or a scorcher?

The Met Office has recently released its contingency planners’ outlook covering the period for June, July and August, with some sources suggesting this is predicting a summer heatwave.

But what does this early look at what might be in store for the summer actually say?

This summer, long-range weather systems show a slight increase in the chance of high pressure patterns across the UK and with this we see an increase in the chance of above-average temperatures. The point about the seasonal outlook, however, is that it gives us the more likely trends within the coming season.  As a result, below-average temperatures, although less likely, remain a realistic possibility.  A summer in which temperatures are more frequently slightly above average is the most likely scenario at this stage, but the fact that warmer and cooler outcomes than this are possible is a feature of the kind of information we are dealing with in long-range forecasting .

The outlook also gives an increase in the likelihood of drier-than-average conditions.  The summer period is one of the driest times of year across the UK; with rainfall coming in short, occasionally intense, showery rain affecting some places but leaving nearby locations dry. On balance, below-average rainfall is more likely than above-average rainfall.

Jeff Knight, manager of modelling of climate variability at the Met Office, said: “Our long term outlook for the summer suggests a greater chance that temperatures will be above average, than below average. However, our outlook certainly doesn’t imply a 3-month heatwave. As always with our climate there are likely to be large day-to-day and week-to-week variations the period. This is an outlook for the general themes over the summer and does not give detailed guidance on events like heatwaves.”

Perception of good weather is often more dependent on rainfall amounts than temperature. For example, even though the UK had a run of ‘poor’ summers between 2007 and 2012, half of these summers had temperatures above the long-term average. The long-range outlook is primarily aimed at giving government departments and agencies a forward view of potential weather hazards in the months ahead. As such, it is a risk assessment rather than a more traditional type of forecast of what the weather is going to be. Using evidence from global weather observations and computer forecast systems, we can estimate the chances of different types of UK weather and how they could be modified in the coming months.

When you look back at the average mean temperature for the UK  both 2017 and 2016 saw temperatures above the 13 C long-term average, with 14.5 C and 13.9 C respectively, and for summer as a whole the mean temperature was 14.7 C in 2017 and 14.9 C in 2016, both also above the long-term summer average of 14.4 C

You can find the current forecast on our website or mobile App or follow us on Twitter or Facebook, and as always our forecasts from one day to one month ahead can be relied upon to provide the best guidance on what to expect whatever weather patterns emerge.

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2 Responses to Will summer be a washout or a scorcher?

  1. xmetman says:

    The one thing that your forecast for summer 2018 doesn’t mention is the all important element of sunshine. The summer index [SI] uses sunshine, temperature and rainfall for each of the summer months. The summer index for 2017 was -6. To give you an idea of the scale summer 1976 scored a maximum 48, and the disastrous summer of 1954 scored a -48. The last good summer if you are guided by the SI was that of 2013.

    2017 -6
    2016 +10
    2015 -8
    2014 +24
    2013 +32
    2012 -31
    2011 -24
    2010 +4
    2009 +7
    2008 -9
    2007 -10

    It might be a good if the Met Office good somehow use the various quintiles and terciles for temperature, rainfall and sunshine to forecast what the SI for summer 2018 would be.

    • Hi Bruce

      An interesting thought. If you were to go down a subjective ‘summer index’ route the question becomes how do you weigh the benefit of an extra 1 degree C versus 20 hours of sunshine? Our three month outlook for contingency planners is designed to highlight the risks they may expect to face during the period. Temperature and rainfall are associated with hazards but sunshine isn’t. I’m sure many of us would love to develop the holy grail of an accurate 3-month deterministic weather forecast. But as we keep pointing out, at the moment seasonal forecasts can’t tell you what the weather is going to be. Rather, they are useful for highlighting when impactful heat/cold/flood/drought/wind are more likely than usual.


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