May was wetter than average across much of the UK, and very wet in some regions, which has had a significant bearing on the June outlook. May river flows were normal to above average in most catchments, with the exception of north-east Scotland where flows were below average. The outlook for June suggests that this pattern is likely to persist; flows in southern and central England are likely to remain above average for the time of year, whilst below average flows in north-east Scotland are likely to continue into June. For the summer as a whole, flows are likely to be in the normal range across much of Great Britain, but with a higher likelihood of above normal flows in southern and eastern England, The groundwater situation is unlikely to change substantially through the summer, with above normal levels persisting in the Chalk of central southern England and the Permo-Triassic sandstones of western England and southern Scotland and normal levels elsewhere.
Latest predictions for UK precipitation favour near- or above-average precipitation for June; the forecast for June-July-August as a whole is close to climatology. The probability that UK precipitation for June-July-August will fall into the driest of five categories is close to 15% and the probability that it will fall into the wettest of five categories is around 20% (the 1981-2010 probability for each of these categories is 20%).
River flow patterns in May were generally in the normal range or above (notably so in parts of north-east England and in central southern England), with the exception of north-east Scotland, where flows were below average for the third consecutive month. The one-month outlook is indicative of broadly similar patterns: flows across England and Wales are likely to be normal or above normal, with above normal flows most likely in central, southern and eastern England. Flows are likely to be normal in Wales, northern England and across much of Scotland; although below-normal flows are likely to persist in the north-east of Scotland. The three-month outlook suggests flows are likely to be normal across much of Great Britain, although there is still a high likelihood of above normal flows in southern and eastern England (particularly in groundwater-fed catchments in central southern England); in northern and western areas, flows are likely to be normal to below, with below normal flows most likely in eastern Scotland.
The groundwater level situation in May was similar to patterns observed in April. Levels were above normal in much of the southern Chalk, notably so in some boreholes, and in the Permo-Triassic sandstones of western England and southern Scotland. Elsewhere, levels were generally normal, with the exception of the Chalk of east Yorkshire where levels were below normal (but only marginally so). The outlook for June is for similar patterns to continue, with levels in most aquifers staying within their current ranges. The broad spatial pattern of the three-month outlook is also similar. This continuity reflects the fact that at this time of year, significant groundwater recharge is unlikely and groundwater levels are not strongly influenced by variations in rainfall; levels are therefore likely to fall through the summer months. However, some exceptionally high levels are likely to decrease towards the normal range, and in east Yorkshire currently low levels are likely to tend towards normal following the rainfall in May.