Insured weather losses in the US reached record highs in the early 1990s, leading to major concerns in the insurance industry about the causes, including the possibility of climate change due to global warming. Several studies addressing the interpretation of the record high losses used historical insurance data sets, those for crop-hail losses and others based on the catastrophic events to the property insurance industry, both covering the 1949–1995 period. The past loss values were adjusted by insurance experts for shifting coverage, inflation, and evolving construction practices. The resulting adjusted values of crop loss and costly catastrophes to property both showed similar distributions for 1949–1995, with losses being high in the 1950s and again in the early 1990s. This distribution was found to have a weak relationship with extra-tropical cyclone activity in the US, but most of the recent increase in weather losses to insured property was found to be related to shifting societal factors that have put ever more property at risk in storm-prone areas, including coastal areas and large metropolitan areas. The low property and crop storm losses of the 1966–1985 period had created an incorrect perception of the weather risk in the insurance industry, which did not understand nor appreciate the existence of the decadal-scale fluctuations that exist in climate conditions.

A diagnostic study of two cases of severe thunderstorms in Catalonia (the north-eastern region of Spain) is presented. The first occurred on 24 August 1993. A squall line, with bow echo configuration in the radar images, crossed Catalonia from west to east. Strong winds, large hail up to 7 cm in diameter, and heavy rain producing floods were observed. The meteorological situation was characterized by an upper-level trough approaching Spain from the north-west. This upper trough developed a low, which displaced the warm, dry air located over the Iberian Peninsula towards the east and north-east. The warm, dry air overran the cold, humid Mediterranean air producing a strong inversion (LID) capped by an elevated mixed layer over the western Mediterranean and also over the Ebro valley. Hand-drawn analyses permitted the identification of a secondary trough; a combination of this trough and a jet streak located over Spain was responsible for the mesoscale lifting mechanism that was able to break the LID and maintain the deep convection. The second case occurred on 31 August 1994. A tornado developed over south Catalonia and large hail, up to 5 cm in diameter, also fell. The meteorological situation was also characterised by an upper-level trough advancing from the west towards Spain. Accurate hand-drawn analyses identified a small thermal low over Catalonia leading to strong convergence at low levels. Over the same area, two jet streaks overlapped their left exit and right entrance zones, producing an enhancement of the ascending motion forced by the low-level convergence. However, the typical environment for supercell development was not present over Catalonia. The tornado was probably produced by a non-supercell thunderstorm.

Accurate prediction of thunderstorms during the pre-monsoon season (April-June) in India is essential for human activities such as construction, aviation and agriculture. Two objective forecasting methods are developed using data from May and June for 1985–89. The developed methods are tested with independent data sets of the recent years, namely May and June for the years 1994 and 1995. The first method is based on a graphical technique. Fifteen different types of stability index are used in combinations of different pairs. It is found that Showalter index versus Totals total index and Jefferson's modified index versus George index can cluster cases of occurrence of thunderstorms mixed with a few cases of non-occurrence along a zone. The zones are demarcated and further sub-zones are created for clarity. The probability of occurrence/non-occurrence of thunderstorms in each sub-zone is then calculated. The second approach uses a multiple regression method to predict the occurrence/non-occurrence of thunderstorms. A total of 274 potential predictors are subjected to stepwise screening and nine significant predictors are selected to formulate a multiple regression equation that gives the forecast in probabilistic terms. Out of the two methods tested, it is found that the multiple regression method gives consistently better results with developmental as well as independent data sets; it is a potential method for operational use.

A theoretical model of flow over a change in surface roughness shows that given an average geostrophic wind of between 8 and 13 m s−1 and near-neutral conditions the difference in equilibrium wind speed at 50 m height over roughness of 0.1 m and over the sea surface is about 20% or 2 m s−1. However, in non-neutral conditions the difference between on- and off-shore wind speeds is affected by changes in stability conditions. Using data from an off-shore monitoring project it is shown that flow over sea is typically associated with smaller stability corrections to the logarithmic wind speed profile owing to an increase in the number of near-neutral and unstable observations compared to flow over land. The presence of land is still detectable after flow of 1–2 km off-shore but its effect on stability and therefore the wind speed profile is reduced. The differences between stability climates on- and off-shore are not simple to elucidate since a number of factors such as the orientation of the coastline with regard to the prevailing wind direction, water depth and latitude are probably also important.

Precipitation forecasting experiments have been carried out with HIRLAM, a numerical weather prediction model. The model has been run with three different horizontal gridlengths: 22, 11 and 5.5 km. An attempt has been made to estimate the appropriate magnitude of the horizontal diffusion, which is used to control small-scale noise in the model, by looking at kinetic energy spectra. It is shown that, for the higher resolutions, smoothing the orography gives smoother precipitation patterns. The small-scale precipitation resulting from runs with the original orography has negligible extra skill compared to the smoothed orography runs. The results show that the model is able to forecast good precipitation amounts, even with 22 km gridlengths. No significant improvements occur when the higher horizontal resolutions are used. Experiments have been performed using the tendencies of the physical parameterisations computed on a coarser grid than that of the dynamics. The resulting precipitation patterns are very similar and this indicates a more economical way of integrating the model.

This paper undertakes a preliminary study into the temporal recording of road accidents in adverse weather. Monthly police accident data, by county, have been utilised for England and Wales, and weather-related road accident findings compared with the general weather patterns experienced over the British Isles. The results show that seasonal patterns to weather-related road accidents match the occurrence of hazardous conditions, with regional variations to weather patterns identifiable within the accident data.

‘Koshava’ is a gusty wind of moderate to strong intensity, blowing from a south-easterly direction, over Serbia, Romania and Bulgaria. It is caused by the interaction between the synoptic circulation and the orography of the Carpathian and the Balkan mountains. This paper analyses wind data from an area where the influence the ‘Koshava’ wind is high during periods of maximum duration of ‘Koshava’. The focus of the paper is the examination of urban and suburban effects on ‘Koshava’ and the correlation between the instantaneous maximum wind speed and the hourly mean values. Various empirical distributions are fitted to the daily maximum wind speed and the best fit for each season and site is proposed. The vertical structure of the lower troposphere above a suburban site during the longest period of consecutive days of ‘Koshava’, which occurred in January and February 1972, is considered.

The existing models for predicting road surface temperature are often based on surface energy balance which includes contributions from sensible and latent heat exchanges between the atmosphere and road surface. The similarity theory is usually applied to compute the atmospheric turbulent heat fluxes. However, the theory only applies in horizontally homogeneous situations, which is certainly not the case for road conditions. An investigation is carried out to see how much measured profiles of mean wind and temperature from a road meteorological station deviate from the profiles given by similarity theory. The difference between the data and the theory is revealed by comparing the observed gradients with the theoretical ones. The sign of the vertical gradients of all data and the relationships between two vertical gradients at different levels under near-neutral conditions are examined. It is found that the measured profiles are all systematically different from the theoretical ones. The deviation is discussed within the context of the possible existence of an internal boundary layer. Moreover, detailed temperature profiles were measured to study the development of temperatures in the first 2.5 m. The results show that the sign of the temperature gradient reverses in a layer between 0.8 and 1.4 m and that a large change in temperature occurs in this layer; these effects were probably caused by local advection.