A very short range forecasting system has been developed which integrates nowcasting techniques with Numerical Weather Prediction (NWP) model products to provide forecasts over the UK and surrounding waters up to six hours ahead. There are three main components, producing analyses and forecasts of precipitation, cloud and visibility, respectively. The precipitation rate analysis uses processed radar and satellite data, together with surface reports and NWP fields. The forecast is based on an object advection technique, modified for growth and decay using model products. Related variables, such as precipitation type, are also diagnosed using the NWP fields. The cloud analysis is based largely on satellite imagery and surface reports, the forecast being carried out in a similar way to precipitation rate. The visibility analysis combines surface reports with NWP model fields and satellite imagery: Meteosat during the day and NOAA-AVHRR at night. The forecast is an extrapolation using trends from the NWP model, and relaxing towards the model values themselves. Results show a substantial improvement over both persistence and raw NWP model products.

Smoke pollution from controlled burning of forested areas can be a major problem for populated areas, even those at some distance from the site of the burning. In particular, Perth, the largest city in Western Australia, is affected by smoke from controlled forest burns to the south of the city when meteorological conditions advect smoke over the city. Such controlled burns are extensively carried out on an annual basis in spring, early summer and late autumn by the Western Australian Department of Conservation and Land Management (CALM) in the southwest forests, in order to reduce flammable fuels and mitigate the undesirable social, economic, environmental and human problems caused by destructive wildfires. In this article, results are presented from a mesoscale model prediction of smoke trajectories from a controlled burn event that took place in November, 1995. In this example, two meteorological factors, a strong sea-breeze front and a mesoscale low pressure system, unexpectedly turned the smoke back from its initial trajectory over the ocean to directly over Perth itself. The result was very high smoke concentration levels over the city and associated health concerns to residents as well as disruption to transport including the closing of Perth airport. The mesoscale guidance was very accurate and can provide valuable guidance when run routinely.

Meteorological aspects of a fatal aircraft accident which resulted from collision with a fog-shrouded 132 Kv suspension transmission tower (an electricity pylon) on approach to Coventry Airport are discussed.

Synoptic surface pressure analyses for the Southern Ocean have been raised to a new level of realism by satellite imagery and NWP models, but the rare ship observations remain important analysis ingredients. This is illustrated here with observed and analysis pressures for an icebreaker journey from Hobart (Tasmania) to Dumont d'Urville and McMurdo (Antarctica).

This paper addresses the long-standing problem of plotting atmospheric fronts objectively. A thermodynamic definition of a front is proposed. Time-independent diagnostic quantities are then devised according to this definition. These can be computed from any gridded dataset. Fronts are then plotted, without human intervention, by utilising standard graphics package facilities, such as contouring, to represent the diagnostics. The methodology includes applying threshold criteria to erase automatically fronts which are thermally weak. By tuning these criteria a good match with subjective fronts is obtained. In addition, the objective surface fronts very often coincide with troughs in surface pressure, implying that a thermodynamic definition is sufficient. The objective front-plotting is further developed to recognise split fronts, and ana- and kata-front characteristics. Many examples are presented; these illustrate how objective fronts are potentially a very powerful tool for both forecasting and research. At the Joint Centre for Mesoscale Meteorology plots and animations showing objective fronts have been produced on a daily basis for many months now.

Colocated UHF and VHF wind profiler radars have been operated during the passage of a sharp cold front. The results demonstrate the utility of the profilers, in conjunction with a conceptual model, for identifying and quantifying many of the features commonly associated with such fronts: low-level and upper-level jets, and rearward-sloping warm-conveyor-belt flow with underlying rear-inflow. The UHF radar detected much of the transverse circulation and also the vertical distribution of precipitation, including a possible region of evaporation associated with the dry rear-inflow jet. The VHF radar, in addition to extending the velocity measurements above the level of the precipitation, mapped the tropopause and, in particular, identified a tropopause fold, the position of which corresponded to the origin of the rear-inflow jet detected by both profilers.

Time series of daily precipitation, at Valentia, Ireland, are examined using conditioned chain-dependent processes. The conditioning is carried out using two different indices of large-scale atmospheric circulation. The first conditioning index relates to mean monthly sea level pressure (SLP), conditioned as either above or below the historic monthly mean. The second conditioning index is based on the geostrophic wind direction (GWD), conditioned as being inside or outside the historic storm quadrant for the month. For each conditioning index, there are two conditioned daily models and they differ in the parameters that relate to both occurrence and intensity and therefore to changes in the distribution of monthly total precipitation. The results of conditioning the daily precipitation on SLP are compared with conditioning on GWD. The GWD conditioned model gave similar results to the SLP conditioned model for the wetter months, but performed poorly for the summer season. Combining the two SLP conditioned daily models into an induced model, which is a mixture of the two chain dependent processes, produces a variance for monthly total precipitation that is closer to the observed value than the unconditioned chain-dependent model.

Meteorology education and training Web site

The NWS Training Center (NWSTC) in Kansas City, the Operational Support Facility (OSF) in Norman, and the COMET Program in Boulder, USA, have established meteorology a new education and training Web site:

http://meted.ucar.edu