The Summer 2024 Met Office Convection Nowcasting Testbed

The testbed concept, where researchers, developers, and users work together intensively for several hours at a time on a series of forecasting and verification exercises, is a proven concept for accelerating the development of new tools and forecasting techniques. At the Met Office, testbeds are one of the recommended platforms by which to evaluate decision aids and models, forming a critical part of Science to Services processes, and they have been held annually since 2020.

In summer 2024, a testbed was held at the Met Office to showcase two new observations-based nowcasting tools: the PLUVIA mesoanalysis, which blends observations from a variety of sources and model data to produce gridded fields of near-surface variables, and the PLUVIA cell tracker, which uses volumetric radar data to identify and track individual convective cells. In addition to increasing Operational Meteorologist familiarity with these new tools, the testbed aimed to assess the extent to which these tools provided added value for the nowcasting of convection and associated hazards in the UK.

The testbed included two specific forecasting tasks. Firstly, identification of mesoscale regions within the UK deemed to be at heightened risk of a given convective hazard (usually, 1-hour rainfall totals exceeding a threshold), as identified by a Lead Operational Meteorologist at the start of each testbed day. Teams were asked to define and then refine their delineated risk areas at intervals specified by the Lead Operational Meteorologist. This task was run as a forecast denial experiment, in which access to the abovementioned nowcasting tools was restricted for some groups, and the results compared for groups with and without access to these tools. Secondly, teams were asked to select a location under threat from an existing convective cell, and to predict the 1-hour rainfall accumulation at their selected location, using all available information including that provided by the nowcasting tools.

In this presentation, we will give an overview of the experiments and outline the key results, including details of how the new nowcasting tools were found to add benefit. We will also offer some lessons learned following our experiences of running a testbed of this nature.