The Role of Continental Mesoscale Convective Systems in Forecast Busts within Global Weather Prediction Systems

Abstract

Despite significant, steady improvements in the skill of medium-range weather predictionsystems over the past several decades, the accuracy of these forecasts are occasionally very poor.These forecast failures are referred to as “busts” or “dropouts”. The lack of a clear explanationfor bust events limits the development and implementation of strategies designed to reduce theiroccurrence. This study seeks to explore a flow regime where forecast busts occur over Europe inassociation with mesoscale convective systems over North America east of the Rocky Mountains.Our investigation focuses on error growth in the European Centre for Medium-Range WeatherForecasting’s (ECMWF’s) global model during the summer 2015 PECAN (Plains Elevated Convectionat Night) experiment. Observations suggest that a close, but varied interrelationship can occurbetween long-lived, propagating, mesoscale convection systems over the Great Plains and Rossbywave packets. Aloft, the initial error occurs in the ridge of the wave and then propagates downstreamas an amplifying Rossby wave packet producing poor forecasts in middle latitudes and, in somecases, the Arctic. Our results suggest the importance of improving the representation of organizeddeep convection in numerical models, particularly for long-lived mesoscale convective systems thatproduce severe weather and propagate near the jet stream.

A Modeling Study of an Atmospheric Bore Associated With a Nocturnal Convective System Over China

“…Given the role of MCS in generating forecast errors in global models (e.g., Lillo & Parsons, 2017;Parsons, Lillo, et al, 2019;Rodwell et al, 2013Rodwell et al, , 2018 capturing the mechanisms that determine the nature and maintenance of MCS in weather and climate models deserves significant attention. Nocturnal convection, in particular, has poor predictive skill (e.g., Geerts & co-authors, 2017).…”

Statistical characteristics of Arctic forecast busts and their relationship to Arctic weather patterns in summer

“…This study suggests that users should access the forecast uncertainty using ensemble forecasts and the differences in forecasts among the NWP centers when forecasts are initialized on the GB and AC patterns, especially on AC pattern in recent years. For the European forecast busts, moist processes associated with warm conveyor belt (Grams et al, 2018) and mesoscale convection over North America (Parsons et al, 2019) contribute to the large errors. In addition, Day et al (2019) showed that the deterioration of the Arctic forecast reduces midlatitudes forecast skill during Scandinavian blocking episodes.…”

Investigation of the trigger perturbation for a simulated case of arctic oscillation transition using initial‐condition perturbation denial experiments

“…(2013), Lillo and Parsons (2017), and Parsons et al . (2019) provide results variously implicating mesoscale convective complexes (MCCs), coastal cyclogenesis, and tropical cyclone extratropical transition events. Other examples include Magnusson (2017) and Grams et al .…”

“…Finally, some recent studies have implicated errors with respect to discrete, smaller-scale features as being the ultimate source of "busts" or "dropouts" in the large-scale forecast skill of state-of-the-art operational systems. For example, Rodwell et al (2013), Parsons (2017), andParsons et al (2019) provide results variously implicating mesoscale convective complexes (MCCs), coastal cyclogenesis, and tropical cyclone extratropical transition events. Other examples include Magnusson (2017) and Grams et al (2018), whose results point to individual synoptic features such as jet streaks, cyclogenesis events, and upper troughs.…”