The aim is to evaluate the use of infrared satellite precipitation estimates for nowcasting purposes in the context of a real-time flood-warning scheme. A radar-based calibration technique is described which is applied to the Negri–Adler–Wetzel scheme. This procedure employs radar data over a defined calibration area to estimate, for each satellite image, actual rain-rates to be used in the Negri–Adler–Wetzel scheme. Calibrated satellite estimates obtained from this procedure can be used to diagnose areas of precipitation beyond radar range, thus allowing an extension of precipitation nowcasting lead time. Calibrated estimates are compared with radar rainfall measurements and results are discussed for various sizes of integration area. Calibration reduces consistently both bias and variance of the error of the original Negri–Adler–Wetzel estimates, even for integration areas as small as 2000 km2. This indicates the capabilities of the new technique for nowcasting purposes over medium-sized river basins.

A method to predict extreme roof snow loads is described. The procedure utilizes a combination of recent climate data (antecedent snow water equivalent information), probabilistic precipitation amount forecasts and historical extreme snow water equivalent data. Use of the procedure is illustrated using precipitation amount probabilities derived directly from a statistical (MOS) guidance product and using conditional climatological probabilities, both with a lead time of 36 hours. The procedure is applied across a portion of the north-eastern United States where extreme snow loads during January 1996 resulted in widespread roof damage, injuries, and a death. Based on the 90th percentiles of the forecast precipitation amount distributions, the procedure accurately identified the areas in which greater than 100-year return interval snow loads were observed.

In this study an attempt is made to investigate the upper-tropospheric downstream development over north-west Europe, which leads to surface cyclogenesis in the central Mediterranean. A case study is analysed to demonstrate that the upper-tropospheric downstream development could be closely related to the upper-tropospheric frontogenesis that appears upon the north-eastern flank of a blocking high. The frontogenesis is characterised by a jet streak within a strongly baroclinic zone and a tropopause folding associated with cold stratospheric air intrusion into the troposphere. According to this interpretation, the eddy ageostrophic divergence of eddy geopotential fluxes (dispersion and spreading of eddy kinetic energy), other than friction dissipation and barotropic conversion to the mean flow, is mainly responsible for the loss of kinetic energy from a decaying depression of synoptic scale that has passed the mature stage. This dispersed eddy kinetic energy accumulates in the vicinity of the aforementioned jet streak where it is transferred downstream and further triggers the generation or rejuvenation of a new disturbance.

The increasing accuracy of data from meteorological satellites coupled with the scarcity of tropical raingauge data and the need for information regarding the fundamental tropical seasons (dry and wet), has led to the development of procedures for climatic analysis that incorporate satellite products. A previously designed procedure based on satellite outgoing longwave radiation and raingauge data is modified to characterise each calendar month of a neo-tropical region (Guri, 7.5° N, 62.5° W, 2.5° lat, 2.5° long, Jan 1974 – Dec 1996, Venezuela). The intensities (categories) of the two fundamental tropical seasons are explored by applying a further four-category procedure. Observed runs of categories lasting four, five and six years, not expected in the 23-year period (1974–1996), indicate that there is a degree of persistence. This persistence could provide industry with information that will allow improved annual planning.

The comparative performance of the WASP and MS-Micro/3 airflow models and of the DAMS scoring system in calculating the wind climate in complex forested terrain has been examined. An analysis was carried out of predicted and observed wind speeds collected over 18 months at six monitoring sites in mountainous country in the Cowal Peninsula, western Scotland. Both airflow models and the DAMS system produced variable results: the airflow models were most accurate on exposed hill tops whereas DAMS tended to be more accurate in valleys and lower slopes. Taken as a whole this study showed that the DAMS scoring system performed as well as the other airflow models considered.

Design floods for major dams throughout the world are based on the probable maximum flood (PMF) which results from the probable maximum precipitation (PMP). Estimates of PMP can be made using a number of methods, the most favoured being the hydrometeorological method involving maximisation and transposition of historic storms. In this paper the in situ maximisation and storm transposition approach has been used for estimating PMP for a one-day duration for different locations in India. Based on these PMP values a generalised map of one-day PMP was produced. It was found that one-day PMP over the Indian region varied from 70 cm to 170 cm, with high values in the mountainous areas of the Western Ghats and in some locations in the north-eastern parts. These results are considerably higher than those obtained using statistical analysis of daily rainfall records using Hershfield's method and they have serious implications for dam safety over much of India.

The difficulties of forecasting for flights of hot-air balloons and small airships are discussed, as well as methods which may be used to improve forecast accuracy. The low-wind-speed requirements and details of weather forecasts required for safe flight are near the limits of accuracy of the forecaster, even when aided by computer models. Preparations for the briefing of balloon pilots need to be carefully undertaken.

A small wave on the polar front crossed the Atlantic and experienced strong explosive cyclogenesis on 28 March 1997 when passing over the North Sea. It then progressed eastwards over northern Poland causing severe damage and the death of at least 11 people. A phenomenological study of the event is presented based on a potential vorticity (PV) approach supplemented by a synoptic analysis. Results confirm previous findings about the impact of a dry stratospheric intrusion on the process of explosive cyclogenesis and fit well with the conceptual model described by Browning (1997) concerning diffluent flow cyclogenesis. Also apparent is the role of potential vorticity advection, which is associated with the rapid change of flow pattern in the upper atmosphere. The careful analysis of potential vorticity fields every 100 m suggests that further research is required into fine mesh analysis and wind field retrieval.

A sub-synoptic vortex with characteristics of a tropical storm developed over the area between Italy and Greece, during the period 14–18 January 1995. Satellite imagery revealed that this vortex was associated with spirally distributed bands and a clearly defined ‘eye’. Ship reports and SSM/I retrieved winds show the existence of strong surface winds around the vortex. Simulation of the genesis and life-cycle of the vortex using the Regional Atmospheric Modelling System and the Eta model successfully reproduced the vortex formation, its strength and its path towards the northern African coast. The model results showed the importance of the surface fluxes (sensible and latent heat) in the development of the vortex on the rear side of a parent low-pressure system which was advected towards the east. During the mature stage of the vortex, latent-heat release within the convective motions was the dominant mechanism which sustained the vortex until its landfall.

The present study deals with the thermal mapping technique in a road climatological perspective. The temperature mapping technique is analysed in relation to instrument set-ups, data collecting and possible sources of errors in converting measured radiation to surface temperature values. Furthermore, analyses of thermal mapping recordings are discussed. Factors that give rise to a varying temperature pattern are presented (i.e. road-bed material, radiation and advection), and also how the thermal mapping technique can be used to determine the relative importance of these factors. The conclusion of the study is that the technique is very useful but it is very important to be aware of the limits and different source of errors involved.

Trends and periodicities of annual rainfall for 29 sub-divisions of India and all India (area-weighted average of the sub-divisions) are studied by using the rainfall series for a period of 124 years (1871–1994). The trends are evaluated by using a linear regression technique. To identify the climatic changes, the rainfall series are subjected to 11-year moving averages. These averages show some epochs. From this, it is found that in some sub-divisions the trend in one direction reverses its direction after some years. The years pertaining to these changes are identified and the trends are calculated for the segments of the series. The significance of the trend values are tested. Power spectra are obtained using the maximum-entropy method. The periods in the range 2.0–2.5 years are present in the rainfall series of the sub-divisions to the north of 20 °N, on the west coast, and in Tamilnadu and for all India. This periodicity may be attributed to the quasi-biennial oscillation. Rainfall series of the most of the sub-divisions and all India indicate a triennial cycle. Significant periods in the range from 3.0 to 8.0 years and 8.0 to 12.0 years are also identified.