On 24 May 1993, part of the Iberian Peninsula was affected by convective activity concentrated on the eastern side of a low-level thermal boundary which was orientated north–south. A series of storms evolved into a squall line striking at the province of Guadalajara (Central Spain). The southernmost cell of this mesoscale convective system generated a tornado that hit the city of Sigüenza between 1930 and 1940 UTC. This paper has two objectives. The first aim is to investigate the ingredients (buoyancy, wind shear, vertical distribution of moisture content, and synoptic and mesoscale lifting mechanisms) and the atmospheric agents (mid-upper level trough, low level-boundary, convergence zones, etc.) which favour the production of severe storms. The second one is to analyse information provided by operational remote-sensing systems (satellite, radar and lightning) in order to test and evaluate some conceptual models of severe storms in an operational environment. For the first objective, the ingredient-based methodology will be shown to be a valuable operational approach allowing forecasters to focus on the possibility of a severe event using the appropriate diagnostic or prognosis tools. For the second objective, special attention is given to the suitability of conceptual models associated with convective phenomena and the potential value of such models (lightning charge related to wind shear and radar-based multicell conceptual models) for understanding the observed processes. From an operational viewpoint some problems may arise because of the technical characteristics of the equipment, particularly related to radars (e.g. scanning strategy, distance between radar and targets, and radar signal processing and displaying). Possible guidelines for using volumetric radar data (non Doppler) for deep convection monitoring are suggested for rugged and complex topographical regions.

Surface observations, satellite and radar imagery and cloud-to-ground lightning data are used in an observational study of two cases that produced severe weather in Catalonia (Spain). The first one occurred on 24 August 1993; a squall line crossed Catalonia from west to east producing heavy rain with rates of up to 100 mm h−1 and hail of 7 cm diameter. The observational information provided is a good tool for monitoring the event and issuing a reasonable nowcast. The second case, which occurred on 31 August 1994, was associated with the development of a tornado (F1 in the Fujita scale) as well as hail of up to 5 cm diameter. In this case the convection was almost stationary and no clear signatures of severe weather can be identified from available satellite and radar imagery.

In an attempt to improve short-range weather predictions in Central Europe, a research project was carried out in Austria which involves adapting the WELS weather prediction system to the Central European environment. This PC-based system is currently in operational use in parts of the United States, chiefly in support of winter highway maintenance operations. The system rests upon the concept of hybrid modelling: an independent, grid-based mesoscale forecast model, integrating the full set of prognostic equations, delivers a prediction which can, in combination with topographic properties, be visualised by a Graphical User Interface (GUI). This post-processing tool seems to have a promising future, especially because it includes the opportunity of adjusting the output of the prediction model; also, locally generated observations can be incorporated into the forecasting process. The use of the forecast-manipulation facilities is appropriate if the prediction seems to be off-track; the time-consuming rerun of the entire forecast model in the case of derailing predictions can be avoided.

A poor forecast of an ex-tropical depression over the UK is examined. The water vapour imagery presented strongly implied an evolution diverging from the operational NWP forecast; it is suggested that such image sequences can be used to monitor upper level flow evolution for early warning of trough disruption.

A short review paper is presented for the subject area of air quality modelling. The paper is geared towards equipping new researchers and workers with a basic appreciation for the technical aspects of their field, providing a staging point for further investigation, and highlighting useful source materials. The paper is introduced through a discussion of the philosophical and practical implications regarding mathematical air quality modelling. A critique of relevant mathematical modelling techniques is presented and includes a treatment of Box, Gaussian, Eulerian, Lagrangian and Particle modelling approaches. Conclusions on the future of mathematical air quality modelling are drawn.

There have been significant reforms in New Zealand of government management in general and of the science and transport sectors in particular. The impact of the reforms on the provision of meteorological services is discussed as an example of the application of the general reform thrust to a specialist technical area. The eventual outcome was the establishment of Meteorological Service of New Zealand Ltd (MetService) as a commercial company, trading in the weather forecasting market but remaining under Crown ownership. At the same time the National Institute of Water and Atmosphere (NIWA) was established. It includes the climatic responsibilities and much of the scientific research component of the former NZMS. It too operates commercially and is Crown owned. Unlike MetService, NIWA is not required to return a dividend to its owners. The procedures leading to the establishment of these new organisations, their mode of operation and their initial successful performance are described.

Weather radar images were used in an investigation of the rainfall events which gave rise to various damaging UK floods in the 1990s. Radar data of sufficient quality were available for seven events from an initial list of 26. The relative temporal and spatial rainfall profiles of each event are displayed and summarised, along with the antecedent catchment wetnesses. Catchment rainfall totals were obtained from daily raingauges. These characteristics are compared with their equivalents in a standard method of flood estimation, the design event method of the Flood Studies Report. The results highlight the complexity of rainfall fields. The wide variety of event characteristics includes some large deviations from their counterparts in the design event. Six of the catchments were modelled with the design event method in order to assess the significance of the deviations in terms of the estimated flood peaks. The rainfall depth and duration and the antecedent catchment wetness were found to have a significant influence within the design event method. The temporal profile was of lesser importance, for most of the events studied.

Surface precipitation-rate estimates derived from radar data are potentially of considerable value to high-resolution Numerical Weather Prediction (NWP) models. This paper describes a scheme developed to assimilate precipitation rates derived from the UK weather radar network into the UK Met. Office Mesoscale Model, with the aim of improving the analysis and forecast of precipitation. It is based on 'latent heat nudging', in which the model profiles of latent heating are scaled by the ratio of observed and model precipitation rates. This causes the model to adjust so that the diagnosed precipitation rate agrees more closely with observations.

The assimilation algorithm is outlined, and the results of a trial of the scheme are described. The scheme brings an increase in forecast skill for precipitation distribution in the first six to nine hours of the forecast, a conclusion supported both by objective verification against radar data and subjective assessment of 14 forecasts. The main benefit was found to occur in frontal cases. The scheme was implemented operationally on 16 April 1996.

Experimental model forecasts conditions every 10 kilometres

The National Weather Service (NWS) in the USA has begun testing a new experimental computer model that will assist forecasters to predict weather conditions across the western United States with more detail than ever before. The model, known as the Eta-10, allows forecasters to monitor the development of weather systems down to a 10-km grid.