Fig P3. *1mm/day = 31mm accumulation in May = 92mm accumulation in May Jul

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1 Met Office 3 month Outlook Period: May July 2014 Issue date: Fig P1 3 month UK outlook for precipitation in the context of the observed annual cycle The forecast presented here is for May and the average of the May June July period for the United Kingdom as a whole. The forecast for May will be superseded by the long range information on the public weather forecast web page ( starting from 2. This forecast is based on information from observations, several numerical models and expert judgement. SUMMARY PRECIPITATION: Latest predictions for UK precipitation are largely indistinguishable from climatology for both May and May June July as a whole. The probability that UK precipitation for May June July will fall into the driest of our five categories is between 20% and 25% and the probability that it will fall into the wettest category is close to 25% (the probability for each of these categories is 20%). CONTEXT: Climatologically late spring and early summer are the driest May June July 2012 are considered low (note how very few of 200 parts of the year, as shown in Figure P1. the blue crosses on the right hand panel of Figure P2 are as As discussed in the temperature section, no single forcing high as the grey cross labelled 2012). However, late spring factor appears dominant and at the same time computer and summer rainfall is often showery in nature so significant model signals are weak. regional variability is often likely. 100 Given this lack of signal for any particular atmospheric circulation type, specific regional variation in forecast rainfall relative to average cannot be predicted. Over the 3 month period, May June July, the precipitation probabilities are largely indistinguishable from climatology, as indicated by the right hand side graph in Figure P2. This means that the probability of the exceptionally wet conditions of Precipitation 3 month UK average accumulation (mm) FMA MAM AMJ MJJ Observations JJA JAS ASO SON OND NDJ DJF JFM FMA MAM AMJ MJJ 3 month periods Average Observation outlook: 3-MONTH OUTLOOK May Jul Fig P2 Precipitation monthly UK average accumulation (mm) 1 month and 3 month UK outlook for precipitation in the context of obser ved climatology 140 May WETTER 400 May July WETTER Fig P Precipitation 3 month UK average accumulation (mm) 150 Average daily precipitation* (mm/day) month and 3 month UK outlook for precipitation in the context of recent climatology: year to year and within season variability 1-MONTH OUTLOOK 3-MONTH OUTLOOK DRIER 0 50 Observations Average 2014 outlook: May May Jul Observations DRIER *1mm/day = 31mm accumulation in May = 92mm accumulation in May Jul Observed averages: 2003 May Jul 2005 May 2007 Years Jun Jul outlook: May May Jul This Outlook provides an indication of possible temperature and rainfall conditions over the next 3 months. It is part of a suite of forecasts designed for contingency planners. The Outlook should not be used in isolation but should be used with shorter range and more detailed (30 day, 15 day and 1 to 5 day) forecasts and warnings available to the contingency planning community from the Met Office.

2 Met Office 3 month Outlook Period: May July 2014 Issue date: Fig T1 3 month UK outlook for temperature in the context of the observed annual cycle The forecast presented here is for May and the average of the May June July period for the United Kingdom as a whole. The forecast for May will be superseded by the long range information on the public weather forecast web page ( starting from 2. This forecast is based on information from observations, several numerical models and expert judgement SUMMARY TEMPERATURE: Latest predictions for UK mean temperature favour near or above average temperatures for May; the forecast for May June July as a whole is largely indistinguishable from climatology. Overall, the probability that the UK mean temperature for May June July will fall into the warmest of our five categories is around 25% and the probability of falling into the coldest of our five categories is close to 20% (the probability for each of these categories is 20%). CONTEXT: Although there are currently no significant sea surface temperature anomalies across the tropical Pacific, latest observations continue to support model predictions that a transition to El Niño conditions is more likely than not later this year. At this stage it is too early for El Niño to exert an influence on European weather for the rest of this spring and during early summer, but should El Niño conditions develop they will start to influence global weather patterns later this year. Factors that can influence the UK's weather during the late spring and early summer currently provide no clear indication of likely dominant weather types during this period. Likewise, computer model signals are indistinct regarding likely atmospheric circulation types affecting Britain during the coming months. Average UK temperature (Celsius) Overall the ensemble forecast shows a weak preference for slightly 6 higher than average frequency of blocked weather patterns over or near the UK for at least part of late spring and early summer. This lends some support to the increased likelihood of near or 3 above average temperatures in May, leaving most likely warmer than May 2013 (note how very few of the red crosses on the left hand panel of Figure T2 are as low as the grey cross labelled 2013). 0 FMA MAM AMJ MJJ JJA JAS ASO SON OND NDJ DJF JFM FMA MAM AMJ MJJ Taking the May June July period as a whole there is very little evidence to separate the forecast temperature distribution from the 3 month periods climatological distribution, as shown in Figure T2. Observations Average Observation outlook: MONTH OUTLOOK May Jul Fig T2 1 month and 3 month UK outlook for temperature in the context of observed climatology Fig T3 1 month and 3 month UK outlook for temperature in the context Average UK temperature (Celsius) May May July Average UK temperature (Celsius) Average UK temperature (Celsius) of recent climatology: year to year and within season variability 1-MONTH OUTLOOK 3-MONTH OUTLOOK 8 7 COOLER Observations Average Observations Years 2014 outlook: May May Jul Observed averages: May Jul May Jun Jul 2014 outlook: May May Jul This Outlook provides an indication of possible temperature and rainfall conditions over the next 3 months. It is part of a suite of forecasts designed for contingency planners. The Outlook should not be used in isolation but should be used with shorter range and more detailed (30 day, 15 day and 1 to 5 day) forecasts and warnings available to the contingency planning community from the Met Office.

3 Outlook based on hydrological persistence and analogy Period: July 2014 Overview SUMMARY The outlook for May and for May to July are for above normal flows in most of the slowly responding Chalk catchments in southeast England. Flows elsewhere are largely expected to be normal to below normal. Few forecasts are available for the northwest for the three-month outlook. RIVER FLOW ANALOGY 1-month flow outlook Outlooks from hydrological analogues are based on a comparison of river flow during recent months with flows during the same months in previous years at a set of approximately 90 sites from across the UK. These sites are depicted on the two maps. Years with observed flows that most closely resemble current conditions are identified as the best analogues and the outlook is based on extrapolating from current conditions based on these analogues. It is, however, often the case that a simpler forecast based on the persistence of river flow provides a better forecast than provided by analogy. This is particularly true for slowly responding catchments associated with aquifer outcrops. Both methods are considered at each site and the forecast from the method with the higher confidence is presented. A simple classification of flows is used (high, medium and low) as indicated by the colours of the dots, with the confidence 3-month flow outlook of the forecast being represented by the size of the dot. A tag on the dot indicates which method has been used in each instance.

4 These figures provide insight into the hydrological analogue methodology for a set of sites from across the UK. Outlook based on hydrological persistence and analogy Period: In each of the time series graphs the bold black line represents the observed flow during the past nine months. The grey band indicates the normal flow range (the normal band includes 44% of observed flows in each month). The selected analogues are shown as thin lines and the trajectories that flows took in the following month are also shown. The forecast is shown as the dashed red line, and in each plot it states whether this has come from the analogues or has been generated on the basis of persistence. Site-based: 1 month outlook RIVER FLOW ANALOGY

5 These figures provide insight into the hydrological analogue methodology for a set of sites from across the UK. In each of the time series graphs the bold black line represents the observed flow during the past nine months. The grey band indicates the normal flow range (the normal band includes 44% Outlook based on hydrological persistence and analogy Period: July 2014 of observed flows in each month). The selected analogues are shown as thin lines and the trajectories that flows took in the following three months are also shown. The forecast is shown as the dashed red line, and in each plot it states whether this has come from the analogues or has been generated on the basis of persistence. Site-based: 3 month outlook RIVER FLOW ANALOGY

6 Avon Wye Severn Outlook based on modelled flow from historical climate Period: August 2014 April 2015 Overview Issued on using data to the 30th April SUMMARY In the East, conditions over the next year are close to those expected. The situation is similar for some catchments in the west, but notable exceptions including medium responding catchments (e.g. Avon) and larger catchments show higher flows than usual expected to continue over at least the next 9 months. Lune FLOW FROM HISTORICAL CLIMATE Ure Trent This outlook is based on monthly ensembles of historical sequences of observed climate (rainfall and potential evapotranspiration) that form input to hydrological models. The outputs are probabilistic simulations of the average river flow over the forecast horizon (3 to 12 months ahead), at each location. The graphs show variation over time of the number of simulated river flow, in each monthly ensemble, that fall within each the seven categories: exceptionally low, notably low, below normal, normal, above normal, notably high and exceptionally high. The monthly variations can be compared to the long-term average distribution of river flow, which are shown as columns on the left and right of each graph. This outlook is based entirely on historical sequences and therefore, this is not a forecast. It does not contain any knowledge of the state of the atmosphere and ocean. It is hence possible that some of the historical sequences used might be inconsistent with current large-scale atmospheric conditions and would therefore be unlikely to occur in the next few months.

7 Outlook based on Modelled Flow from Rainfall Forecasts The regional maps illustrating the regional river flows for five members of the Met Office ensemble of rainfall forecasts give some indication of the range of possible river flows in the coming months. As noted previously, the actual flows could be more extreme than the flows generated by either the lowest or highest members of the rainfall ensemble. The bar charts (below) give further insight into the range of river flow forecasts by considering all members of the forecast rainfall ensemble. The regional bar charts show the percentage of ensemble forecasts falling in each of the flow categories as generated by the monthly-resolution water-balance model. As before results are averaged by region then ranked in terms of 49 years of historical regional flow estimates ( ). SUMMARY Following typically variable April rainfall, mean April flows across Britain have tended towards normal levels. In May, forecasts suggest a >60% chance for England and Wales river flows to be in the normal range or above (except Anglia, 50% chance), while in Scotland flows are more variable and there is a greater chance they will be normal or lower. In some parts of the UK (Tweed, Northumbria, Wessex and Thames) there is a 25% chance that flows will be notably high or exceptional. Over the next 3 months it is likely ( 50% chance) that river flows will be normal or below normal. There is a 10% chance that flows in Southern, Thames and Wessex regions will be exceptionally high. Conversely, there is a >20% chance of exceptionally low flows in Northwest and Highlands. Period: From Issue date: month 3-month 1- and 3-month variability SCOTLAND HR Highlands Region NER North East Region TR Tay Region FR Forth Region CR Clyde Region TWR Tweed Region SR Solway Region ENGLAND N Northumbria NW North West Y Yorkshire ST Severn Trent A Anglian T Thames S Southern W Wessex SW South West WALES WEL Welsh NORTHERN IRELAND This method cannot currently be used in Northern Ireland RIVER FLOW FROM RAINFALL FORECASTS example The Hydrological Outlook UK provides an outlook for the water situation for the UK over the next three months and beyond. For guidance on how to interpret the outlook, a wider range of information, and a full

8 Outlook based on modelled groundwater level & climate forecast Period: July 2014 SUMMARY Groundwater levels should generally continue to recess over the next 1 to 3 months and climatic influences on groundwater levels should weaken. Areas with current high groundwater levels, such as in the Chalk of southern England and the Permo-Triassic sandstone basins of the English and Scottish Borders will remain high while most levels will start to return to normal. Groundwater levels in the Chalk of Lincolnshire and Yorkshire will be slightly below average. Lowest rainfall forecast 1 st quartile Median 3 rd quartile Highest rainfall forecast Overview These forecasts are produced by running five members of the Met Office ensemble climate forecast through groundwater models of observation borehole hydrographs at 25 sites across the country. The sites are distributed across the principal aquifers. Based on the distribution of observed historical groundwater levels in a given month, seven categories have been derived for each site: very low, low, below normal, normal, above normal, high, and very high. The forecast groundwater level is assigned to one of these seven categories depending on where it falls within the distribution of the historically observed values. Key Percentile range of historic observed values for relevant month Exceptionally high levels > 95 Notably high levels Above normal Normal Below normal Notably low levels 5-13 Exceptionally low levels < 5 GROUNDWATER FROM CLIMATE FORECASTS 1-month outlook Lowest rainfall forecast 1 st quartile Median 3 rd quartile Highest rainfall forecast 3-month outlook

9 Rockley (SU17/57) Heathlanes (SJ62/112) Skirwith (NY63/2) Outlook based on modelled groundwater from historical climate Period: April 2015 SUMMARY Over the summer groundwater levels in the Chalk are expected to remain relatively high and not return to normal levels until early Groundwater levels in the Permo-Triassic sandstone are expected to stay at or above normal range at least until Spring 2015 due to the high cumulative rainfall over the last 18 months. Dalton Holme (SE94/5) Washpit Farm (TF81/2A) GROUNDWATER FROM HISTORICAL CLIMATE This outlook is based on monthly ensembles of historical sequences of observed climate (rainfall and potential evapotranspiration) that form input to hydrological models. The outputs are probabilistic simulations of the average groundwater level over the forecast horizon (3 to 12 months ahead), at each location. that fall within each the seven categories: exceptionally low, notably low, below normal, normal, above normal, notably high and exceptionally high. The monthly variations can be compared to the long-term average distribution of levels, which are shown as columns on the left and right of each graph. Little Bucket Farm (TR14/9) knowledge of the state of the atmosphere and ocean. It is hence possible that some of the historical sequences used might be inconsistent with current large-scale atmospheric conditions and would therefore be unlikely to occur in the next few months. The graphs show variation over time of the number of simulated groundwater levels in each monthly ensemble, This outlook is based entirely on historical sequences and therefore, this is not a forecast. It does not contain any The Hydrological Outlook UK provides an outlook for the water situation for the UK over the next three months and beyond. For guidance on how to interpret the outlook, a wider range of information, and a full