Monthly or annual 5 km × 5 km gridded datasets covering the UK are generated for the 1961-2000 period, for 36 climatic parameters. As well as the usual elements of temperature, rainfall, sunshine, cloud, wind speed, and pressure, derived temperature variables (such as growing-season length, heating degree days, and heat and cold wave durations) and further precipitation variables (such as rainfall intensity, maximum consecutive dry days, and days of snow, hail and thunder) are analysed.The analysis process uses geographical information system capabilities to combine multiple regression with inversedistance-weighted interpolation. Geographic and topographic factors, such as easting and northing, terrain height and shape, and urban and coastal effects, are incorporated either through normalization with regard to the 1961-90 average climate, or as independent variables in the regression. Local variations are then incorporated through the spatial interpolation of regression residuals.For each of the climatic parameters, the choice of model is based on verification statistics produced by excluding a random set of stations from the analysis for a selection of months, and comparing the observed values with the estimated values at each point. This gives some insight into the significance, direction, and seasonality of factors affecting different climate elements. It also gives a measure of the accuracy of the method at predicting values between station locations.The datasets are being used for the verification of climate modelling scenarios and are available via the Internet.  Crown

Monthly and annual long-term average datasets of 13 climate variables are generated for the periods 1961-90 and 1971-2000 using a consistent analysis method. Values are produced for each station in the Met Office's observing network and for a rectangular grid of points covering the UK at a horizontal spacing of 1 km. The variables covered are mean, maximum, minimum, grass minimum and soil temperature, days of air and ground frost, precipitation, days with rain exceeding 0.2 and 1 mm, sunshine, and days with thunder and snow cover.Gaps in the monthly station data are filled with estimates obtained via regression relationships with a number of well-correlated neighbours, and long-term averages are then calculated for each site. Gridded datasets are created by inverse-distance-weighted interpolation of regression residuals obtained from the station averages. This method does not work well for days of frost, thunder and snow, so an alternative approach is used. This involves first producing a grid of values for each month from the available station data. The gridded long-term average datasets are then obtained by averaging the monthly grids.The errors associated with each stage in the process are assessed, including verification of the gridding stage by leaving out a set of stations. The estimation of missing values allows a dense network of stations to be used, and this, along with the range of independent variables used in the regression, allows detailed and accurate climate datasets and maps to be produced. The datasets have a range of applications, and the maps are freely available through the Met Office Website.  Crown

In order to test the current recommendation for reservoir safety that a snowmelt of 42 mm/day can be used throughout the UK, calculations of hourly snowmelt rates were made for hourly weather reporting stations in the UK. These data were analysed to give annual maximum melt totals for periods of 3, 6, 9, 12, 18, 24, 48, 72, 120 and 168 hours. Supplementary data from high altitude climate stations allowed further 24‐hour melts to be calculated. The annual maxima were entered into an extreme value type one (Gumbel) analysis and estimates of the melt with return periods of 5, 20 and 50 years were made for the durations of 3, 6, etc. hours. An estimate of the return period of a 24‐hour melt of 42 mm was made for the sites. These return periods were below 10 years in some high altitude Pennine and Scottish sites, but in excess of 1000 years at low altitude in England. The 24‐hour melt with 5 year return period at the sites was related to altitude, northing, mean January temperature and windspeed in linear regressions which permit a calculation of snowmelt at any point in the UK. Copyright © 1998 Royal Meteorological Society