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Julian F. Quinting, Michael M. Bell, Patrick A. Harr, and Sarah C. Jones

) showed that operational global numerical models do not properly simulate these structural changes. However, the dynamical processes that are associated with these structural changes perturb the midlatitude flow. In idealized simulations Riemer et al. (2008) showed that these complex perturbations to the midlatitude flow may result in a baroclinic downstream development. Real case ensemble forecasts indicate that initially small perturbations may lead to plumes of forecast uncertainty in downstream

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Simon T. K. Lang, Sarah C. Jones, Martin Leutbecher, Melinda S. Peng, and Carolyn A. Reynolds

). For the EPS, SVs are calculated for the extratropics of the Northern and Southern Hemisphere. Extra sets of SVs are added for tropical cyclones (TCs) ( Puri et al. 2001 ). A further area where SV techniques are applied is for targeted observations ( Palmer et al. 1998 ; Leutbecher 2003 ). SV calculations are carried out usually at relatively low resolution [T42 (≈320 km) for the operational EPS] and therefore the forecast used to calculate the SVs is not able to represent a TC properly because of

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Andreas Schäfler, Andreas Dörnbrack, Christoph Kiemle, Stephan Rahm, and Martin Wirth

1. Introduction During the last few decades, forecasts of operational numerical weather prediction (NWP) models have continuously improved as a result of an enhanced spatial resolution and advanced parameterization schemes for the model physics. Furthermore, the global coverage of spaceborne remote sensing observations and their assimilation has rapidly improved the forecast skill ( Simmons and Hollingsworth 2002 ). However, the representation of cloud processes involving the condensation of

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Tobias Selz and George C. Craig

gravity waves radiating from convective regions in upscale growth or errors will be discussed. 2. Experimental design This study employs a nonhydrostatic limited-area atmospheric model provided by the Consortium for Small-Scale Modeling (COSMO) ( Baldauf et al. 2011 ). It has been applied for many years by the German Meteorological Service [Deutscher Wetterdienst (DWD)] for operational forecasting with a 7-km grid spacing (COSMO-EU) and a 2.8-km grid spacing (COSMO-DE). In the higher

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Julia H. Keller, Christian M. Grams, Michael Riemer, Heather M. Archambault, Lance Bosart, James D. Doyle, Jenni L. Evans, Thomas J. Galarneau Jr., Kyle Griffin, Patrick A. Harr, Naoko Kitabatake, Ron McTaggart-Cowan, Florian Pantillon, Julian F. Quinting, Carolyn A. Reynolds, Elizabeth A. Ritchie, Ryan D. Torn, and Fuqing Zhang

transport, which may impact both the occurrence frequency and predictability of subseasonal regimes on basin to hemispheric length scales. The Subseasonal to Seasonal Project database ( www.s2sprediction.net ; Vitart et al. 2017 ), which provides access to subseasonal to seasonal forecasts from 11 operational centers, could be a valuable resource for such investigations. On still longer time scales, the influence of a warming climate on the downstream impact of ET, in particular, is another aspect that

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Maxi Boettcher and Heini Wernli

Storms” in 1991 ( Cordeira and Bosart 2011 ). Investigation of different operational forecasts for one of these DRWs revealed that the low-level baroclinicity downstream and the moisture to the south of the system were found to be the most important factors leading to the DRW propagation ( Boettcher and Wernli 2011 ). Sensitivity experiments where the moist diabatic processes were turned off, led to much weaker systems and no subsequent explosive intensification ( Wernli et al. 2002 ; Moore et al

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Volkmar Wirth, Michael Riemer, Edmund K. M. Chang, and Olivia Martius

; moreover, the forecast became rather poor after a lead time of as little as 5 days. The latter result seems to be at odds with the commonly held view that large-scale phenomena such as RWPs should be predictable on a rather long time scale. However, this evaluation was for a single case only involving a single forecast model; further systematic studies are required to possibly generalize these results. Regarding the waveguide, several operational forecast models are fraught with a spurious decrease of

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Julian F. Quinting and Sarah C. Jones

. Meteor. Soc. , 128 , 93 – 117 , doi: 10.1256/00359000260498806 . Evans , J. L. , and R. E. Hart , 2003 : Objective indicators of the life cycle evolution of extratropical transition for Atlantic tropical cyclones . Mon. Wea. Rev. , 131 , 909 – 925 , doi: 10.1175/1520-0493(2003)131<0909:OIOTLC>2.0.CO;2 . Evans , J. L. , J. M. Arnott , and F. Chiaromonte , 2006 : Evaluation of operational model cyclone structure forecasts during extratropical transition . Mon. Wea. Rev. , 134

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Franziska Teubler and Michael Riemer

, such a pattern can be expected to yield ridge amplification and a hindrance and deformation of the upstream trough. d. Direct diabatic modification Diabatic processes have a direct impact on the PV distribution by modifying θ gradients—a mechanism that is represented by diabatic terms in the PV-tendency equation. Different contributions to the diabatic generation of PV anomalies in an operational forecast model have been investigated in detail by Chagnon et al. (2013) and Chagnon and Gray

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Christian M. Grams and Heather M. Archambault

national weather services in Europe ( http://cosmo-model.org/ ) and which is comparable to the Weather Research and Forecasting (WRF) Model. Most physical processes (e.g., subgrid-scale turbulence, radiation) are parameterized following the operational setup. In adaptation to the investigation of ET on large domains we use a Kain–Fritsch scheme ( Kain and Fritsch 1993 ) for the representation of moist convection and a Kessler-type bulk microphysics scheme ( Kessler 1969 ) with six categories of water

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