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Kevin Bachmann, Christian Keil, George C. Craig, Martin Weissmann, and Christian A. Welzbacher

1. Introduction Convection-permitting numerical weather prediction (NWP) models underpin a step change for operational forecasting centers in their struggle to predict thunderstorms and convective precipitation ( Clark et al. 2016 ) as they allow some key issues to be addressed. First, the intrinsically limited predictability of the small scales, including convection, necessitates the use of ensembles to generate probabilistic forecasts and assess their confidence ( Lorenz 1969 ; Slingo and

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Michael Maier-Gerber, Michael Riemer, Andreas H. Fink, Peter Knippertz, Enrico Di Muzio, and Ron McTaggart-Cowan

were associated with the TT of Chris, before the results in terms of predictability are presented in section 4 . The findings and conclusions from this study are discussed in section 5 . 2. Data and methods a. Data The present case study is based on gridded, 6-hourly operational analysis and ensemble forecast data from the ECMWF. To assess the evolution of predictability, consecutive ensemble forecasts initialized at 0000 UTC between 10 June and 19 June 2012—equivalent to 9.5 (7) days prior to

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Marlene Baumgart, Paolo Ghinassi, Volkmar Wirth, Tobias Selz, George C. Craig, and Michael Riemer

1. Introduction Weather prediction has improved significantly in the past decades ( Bauer et al. 2015 ). Forecast dropouts, however, do still occur in operational numerical weather prediction models ( Rodwell et al. 2013 , 2018 ). Because of the multiscale nature of atmospheric dynamics, there may always be an intrinsic limit of predictability even if model errors and initial-condition errors occur only on the smallest resolved scale ( Lorenz 1969 ). Small-scale errors associated with moist

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Stephan Rasp and Sebastian Lerch

1. Introduction Numerical weather prediction based on physical models of the atmosphere has improved continuously since its inception more than four decades ago ( Bauer et al. 2015 ). In particular, the emergence of ensemble forecasts—simulations with varying initial conditions and/or model physics—added another dimension by quantifying the flow-dependent uncertainty. Yet despite these advances the raw forecasts continue to exhibit systematic errors that need to be corrected using statistical

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Marlene Baumgart, Michael Riemer, Volkmar Wirth, Franziska Teubler, and Simon T. K. Lang

. Res. , 101 , 1435 – 1456 , . 10.1029/95JD02674 Bauer , P. , A. Thorpe , and G. Brunet , 2015 : The quiet revolution of numerical weather prediction . Nature , 525 , 47 – 55 , . 10.1038/nature14956 Boer , G. J. , 1984 : A spectral analysis of predictability and error in an operational forecast system . Mon. Wea. Rev. , 112 , 1183 – 1197 ,<1183:ASAOPA>2.0.CO;2 . 10

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Mirjam Hirt, Stephan Rasp, Ulrich Blahak, and George C. Craig

, we retune the perturbation amplitude α tuning to 1.5 to match the precipitation amplitude of the original PSP scheme. For operational use, this choice would have to be revisited to produce the best overall precipitation forecast over a long test period. Although a clear overall improvement in forecast skill scores was not demonstrated in the preliminary evaluation here, the specific impacts of the changes to the scheme were as expected. In particular, PSP2 maintains the desired effect of the

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Stephan Rasp, Tobias Selz, and George C. Craig

( section 6 ). We conclude with a summary and discussion of our results in section 7 . 2. Methods To investigate the mesoscale structure of parcel ascent, numerical simulations were conducted with the nonhydrostatic, limited-area weather forecasting model,Consortium for Small-Scale Modeling (COSMO; Baldauf et al. 2011 ), which, following the COSMO-DE operational setup, has a horizontal grid spacing of 2.8 km and 50 terrain-following levels in the vertical. The vertical grid spacing decreases from

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Christian Euler, Michael Riemer, Tobias Kremer, and Elmar Schömer

. During the simulation, Karl moves northeast and farther away from the boundary. As boundary conditions, as well as initial conditions, we use archived operational analysis data from the European Centre for Medium-Range Weather Forecasts. A comparison of the model track and intensity with the best track analysis by the National Hurricane Center (NHC; Pasch and Zelinsky 2016 ) shows that shortly after recurvature, between 1200 UTC 24 September and 0000 UTC 25 September, Karl in the COSMO simulation

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Paolo Ghinassi, Georgios Fragkoulidis, and Volkmar Wirth

bust” for the majority of the operational forecast models, showing a huge drop in the medium-range forecast skill over Europe ( Rodwell et al. 2013 ). The authors associated this poor performance to the misrepresentation of moist convective processes over North America a few days earlier, and this error was subsequently communicated downstream embedded in a RWP. Data are retrieved from the ERA-Interim reanalyses ( Dee et al. 2011 ) with a horizontal resolution of 2° × 2° on 20 pressure levels

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Gabriel Wolf and Volkmar Wirth

wave breaking toward the end of the life cycle resulted in the formation of a cutoff cyclone over Europe, which led to the heavy precipitation event. The rain was poorly forecast by the operational centers even on the relatively short time scale of a few days ( Grazzini and van der Grijn 2002 ). Assuming that large-scale and long-lived dynamical features should generally be predictable on a time scale longer than just a few days, this suggest that there may be room for improvements concerning the

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