Summer is a time when many look forward to enjoying the great outdoors, but all too often the British weather can, quite literally, dampen our spirits. The Met Office has just released its contingency planners’ outlook covering the period for June, July and August. So what can we say based on this early look at what might be in store for the summer?
Currently, the chances of what type of weather we will experience appear fairly balanced. While the outlook suggests a moderate increase in the chances of higher-than-average temperatures, that can’t be taken as indicating a strong likelihood of a hot summer. Indeed, the perception of good weather often relates to the seasonal rainfall. 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. Looking forward to this summer, the chances of below- or above-average rainfall appear to be very similar.
It is worth remembering that the 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 how the chances of different types of UK weather will be modified in the coming months. This summer, the outlook suggests that the likelihood of these weather types, and the chance of the weather having a serious impact on us, is close to what we normally expect. It is not saying there is no risk, but it indicates there are currently no reasons to think the usual level of risk is either increased or diminished.
Outlooks for last winter and spring contained significant increases in the chances of particular types of weather compared to normal. Specifically, they pointed to an increased tendency of mild, wet and windy weather in early winter followed by a transition to colder conditions in the late winter and spring. This was indeed the pattern of weather in this period: December turned out to be exceptionally mild and wet for the UK, whilst March and April were colder than the long-term average. So why were there signals favouring particular weather last winter and spring but not now as we approach summer?
The answer lies in influences from other parts of the global climate system. We know that weather in the UK can be modified by effects from far across the globe, and generally a number of these factors combine to produce a shift in the chances of getting particular weather. In winter and spring there were effects like the strong El Niño in the tropical Pacific Ocean, and the state of the stratosphere, both of which have reasonably clear-cut effects on weather in those seasons. Since then, however, we have seen El Niño decline, and whilst there is a growing likelihood that its counterpart La Niña will develop over the summer, it has only a weak link to the UK at this time of year. In fact, the various global phenomena that are now present or are expected to develop all appear to have relatively weak effects on UK weather at this time of year.
So will we get heatwaves or downpours? There is always a chance of either – or both – happening at times in summer, but this summer the chances of experiencing them are currently similar to normal. 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.