The added value of convection‐permitting ensemble forecasts of sea breeze compared to a Bayesian forecast driven by the global ensemble

Abstract

Dynamical downscaling of ensemble forecasts to convection‐permitting resolutions aims to improve forecast skill by explicitly resolving mesoscale dynamical features. The success of this approach is dependent on the ability of the model to spin up smaller features embedded in the larger‐scale flow and provide more local information than could be inferred from knowledge of the climatological response to the large‐scale flow alone. Here we test whether such additional information is obtained from the Met Office Global and Regional Ensemble Prediction Systems (MOGREPS) for the sea‐breeze phenomenon which is resolved properly only at convection‐permitting resolutions but is driven by large‐sale conditions that are well represented in the global driving model. The sea breeze is detected using a new automatic tracking algorithm suitable for use in convective‐scale forecast data. The skill of probabilistic forecasts of sea‐breeze occurrence from the high‐resolution ensemble is compared to that of a Bayesian forecast trained on paired high/low‐resolution ensemble members. This creates a statistical forecast of the high‐resolution ensemble member given knowledge of the global forecast ensemble alone. The aim of this paper is twofold: firstly to assess whether the information about sea‐breeze occurrence is encoded in a few large‐scale parameters and can be forecast by a statistical method, and secondly to estimate what information is gained by running the high‐resolution forecast beyond that which is contained in these large‐scale flow parameters. Comparison of the two forecasting methods using a variety of verification methods all lead to the same conclusion: although both the Bayesian forecast and convection‐permitting ensemble provide information about sea‐breeze occurrence, the convection‐permitting ensemble is significantly more able to discriminate between sea‐breeze events and non‐events for all lead times.

Optimal configuration and resolution for the first convection‐permitting ensemble of climate projections over the United Kingdom

“…Although CPMs do not fully resolve convection (especially smaller showers and convective plumes), they can represent ("permit") larger storms and mesoscale organization of convection explicitly on the model grid much better than the parameterizations of convection. CPMs also have a more detailed representation of topography giving more realistic local winds and convergence lines, for example, sea breezes (Cafaro et al, 2019). The ability of CPMs to give much improved hourly statistics for the right reasons gives us confidence that these models can provide a more reliable insight into future changes in precipitation extremes of short duration that are likely to significantly impact on society.…”

Domino: A new framework for the automated identification of weather event precursors, demonstrated for European extreme rainfall

“…Despite these advantages and the demonstrated value of local flow features in models to predict mesoscale events (Cafaro et al, 2019;Ferrett et al, 2023), there has been relatively little operational use of large-scale flow precursors thus far to improve operational forecasts. One notable exception is the use of regime approaches (Ferranti et al, 2015), which have been shown to boost precipitation forecast skill (Mastrantonas et al, 2021).…”

Classification of synoptic and local-scale wind patterns using k-means clustering in a Tyrrhenian coastal area (Italy)

“…Although the SBR has been widely studied in recent years from both the experimental (Cenedese et al 2000;Puygrenier et al 2005) and the numerical (Fu et al 2021;Di Bernardino et al 2021b) point of view, its identification only relies on subjective and site-specific criteria, impairing the objective separation of the pure sea-breeze contribution to the local circulation from the concurrent synoptic influence, which can disturb, limit or exacerbate the inland penetration of the breeze (Azorin-Molina et al 2011). Only recently, researchers have attempted to isolate the pure sea breeze component by analysing high-resolution models and observations and developing less site-specific criteria and no-threshold methods (Cafaro et al 2019).…”