The one-month and three-month outlooks for parts of south-east England are for below normal groundwater levels and normal to below normal river flows. Elsewhere in the UK, river flows and groundwater levels are most likely to be within the normal range in January and normal to above normal for the January to March period. Whilst below normal river flows are likely in some localised areas, the rainfall over the last fortnight coupled with a forecast for above-average rainfall ensures that, in general for the UK, above normal flows are more likely than below normal flows.
Whilst the UK registered near average rainfall overall in December, there were substantial regional differences. Rainfall in most of Scotland, Northern Ireland and northern England was below average. Further south, much of Wales and central, southern and eastern England was wetter than average.
The Met Office 3-month Outlook issued on 15th December indicated that for January, and January-February-March as a whole, above-average precipitation is more likely than below-average precipitation. The likelihood of impacts from heavy rainfall and high winds is greater than usual. The probability that UK-average precipitation for January-February-March will fall into the driest of five equal categories is 15% and the probability that it will fall into the wettest of five equal categories is 30% (the 1981-2010 probability for each of these categories is 20%).
River flows for December were within the normal range across most of the UK. Above normal flows were registered in parts of northern Scotland and below normal flows characterised parts of eastern Scotland and central southern England.
River flows are likely to be below normal for both January and the January-March period in parts of south-east England and where groundwater is influential on river flows, including streams draining the Chilterns and the headwaters of the Thames. Elsewhere, normal flows are most likely in January and the three-month outlook is for normal to above normal flows. However, there is likely to be considerable localised variations within this general pattern with both above or below normal flows resulting from catchment characteristics, such as the contribution of groundwater to river flows, and recent rainfall variability.
Although groundwater levels increased following wet weather, December levels remained below normal across most of the Chalk aquifer away from the south coast. Elsewhere, levels were mostly in the normal range but notably high in parts of the Limestone towards the headwaters of the Thames.
For the Chalk of the North Downs and through the Chilterns across to Suffolk, below normal levels are likely to persist through January and over the January to March period for all but the wettest of the rainfall forecasts. North of London, notably low levels are very likely in January and more likely than not over the three-month timeframe. Away from this area, levels are most likely to be normal in January and normal to above normal for the January to March period.