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Forecast Range (forecast + range)
Selected AbstractsDetecting and nowcasting cloudiness using near-surface temperatures on winter nightsMETEOROLOGICAL APPLICATIONS, Issue 2 2006Tobias Grimbacher Abstract A model to deduce cloudiness from automatic measurements of synoptic and road weather stations during winter nights is introduced. The (height-adjusted) cloud amount of each station can be determined from near-surface temperature measurements and precipitation information only. By using the difference between the air temperature at surface level and the air temperature 2 m above ground, a correlation coefficient is achieved of up to 0.91 between the calculated cloud amount and observations. The model is applied to a dense network in central Switzerland in order to obtain a two-dimensional cloud map by interpolation. With the help of a tracking algorithm, the displacement of cloud patterns is nowcasted. The procedure was tested using data from winter 2003,4. It works successfully with a forecast range up to about 90 minutes. The results are used to predict a change in surface temperature (in cases with changing cloudiness), and thus allow nowcasting of slippery roads or ground frost. Copyright © 2006 Royal Meteorological Society. [source] Reanalysis and reforecast of three major European storms of the twentieth century using the ECMWF forecasting system.METEOROLOGICAL APPLICATIONS, Issue 2 2005Part II: Ensemble forecasts In Part II of this study the ECMWF Ensemble Prediction System (EPS) is used to study the probabilistic predictability of three major European storms of the twentieth century. The storms considered are the Dutch storm of 1 February 1953, the Hamburg storm of 17 February 1962, and the British/French storm of October 1987 (Great October storm). Common to all these storms is their severity that caused large loss of life and widespread damage. In Part I of this study it has been found that deterministic predictability of the Dutch and Hamburg storms amount to 48 and 84 hours, respectively. Here, it is shown that the ensemble forecasts supplement the deterministic forecasts. The large number of members in the 48 and 84 hour ensemble forecasts of the Dutch and Hamburg storms, respectively, suggest that at this forecast range and for these storms the sensitivity of the forecasts to analysis and model uncertainties is rather small. From these results, therefore, it is argued that reliable warnings (i.e. low probability for the occurrence of a forecast failure) for the Dutch and Hamburg storms could have been issued 48 and 84 hours, respectively, in advance, had the current ECMWF EPS been available. For the Great October storm it has been found in Part I of this study that short-range and medium-range forecasts of the intensity and track of the storm were very skilful with a high-resolution model of the ECWMF model. The actual timing of the storm, however, was difficult to predict. Here, it is shown that the EPS is capable of predicting large forecast uncertainties associated with the timing of the Great October storm up to 4 days in advance. It is argued that reliable warnings could have been issued at least 96 hours in advance had the ECMWF EPS been available. From the results presented in this study it is concluded that an Ensemble Prediction System is an important component of every early warning system for it allows an a priori quantification of the probability of the occurrence of severe wind storms. Copyright © 2005 Royal Meteorological Society [source] Horizontal resolution impact on short- and long-range forecast errorTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 649 2010Roberto Buizza Abstract The impact of horizontal resolution increases from spectral truncation T95 to T799 on the error growth of ECMWF forecasts is analysed. Attention is focused on instantaneous, synoptic-scale features represented by the 500 and 1000 hPa geopotential height and the 850 hPa temperature. Error growth is investigated by applying a three-parameter model, and improvements in forecast skill are assessed by computing the time limits when fractions of the forecast-error asymptotic value are reached. Forecasts are assessed both in a realistic framework against T799 analyses, and in a perfect-model framework against T799 forecasts. A strong sensitivity to model resolution of the skill of instantaneous forecasts has been found in the short forecast range (say up to about forecast day 3). But sensitivity has shown to become weaker in the medium range (say around forecast day 7) and undetectable in the long forecast range. Considering the predictability of ECMWF operational, high-resolution T799 forecasts of the 500 hPa geopotential height verified in the realistic framework over the Northern Hemisphere (NH), the long-range time limit ,(95%) is 15.2 days, a value that is one day shorter than the limit computed in the perfect-model framework. Considering the 850 hPa temperature verified in the realistic framework, the time limit ,(95%) is 16.6 days for forecasts verified in the realistic framework over the NH (cold season), 14.1 days over the SH (warm season) and 20.6 days over the Tropics. Although past resolution increases have been providing continuously better forecasts especially in the short forecast range, this investigation suggests that in the future, although further increases in resolution are expected to improve the forecast skill in the short and medium forecast range, simple resolution increases without model improvements would bring only very limited improvements in the long forecast range. Copyright © 2010 Royal Meteorological Society [source] Monitoring the observation impact on the short-range forecastTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 638 2009Carla Cardinali Abstract This paper describes the use of forecast sensitivity to observations as a diagnostic tool to monitor the observation impact on the 24-hour forecast range. In particular, the forecast error is provided by the control experiments (using all observations available) of two sets of observing system experiments performed at ECMWF, a month in summer 2006 and a month in winter 2007, respectively. In such a way, the observation data impact obtained with the forecast sensitivity is compared with the observing system experiment's data impact; differences and similarities are highlighted. Globally, the assimilated observations decrease the forecast error; locally, some poor performances are detected that are related either to the data quality or to the suboptimality of the data assimilation system. It is also found that the synoptic situation can affect the measurements or can produce areas of large field variability that the assimilation system cannot model correctly. Copyright © 2009 Royal Meteorological Society [source] Impact study of the 2003 North Atlantic THORPEX Regional CampaignTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 615 2006Nadia Fourrié Abstract An experiment took place during autumn 2003 with the aim of testing the feasibility of an operational targeting of observations over the North Atlantic Ocean in the context of the international programme THORPEX. The purpose of this paper is to evaluate the impact of these additional observations in the French operational model ARPEGE during the last three weeks of the campaign. Results are shown for large regions over and around the North Atlantic Ocean and for specific verification areas. Over Europe, the addition of observations is slightly beneficial for the forecast, mostly in the low troposphere over wide areas and above 100 hPa. However, the impact of extra data is more significant but also more mixed for the dedicated verification areas: they are case, forecast-range and level dependent. In addition, the information content is studied with the Degrees of Freedom for Signal (DFS) for the evaluation of the observation impact on the analysis of one case of December 2003. Firstly, the variations of the DFS have been illustrated in a simplified data assimilation system. It has been found for that case that satellite data have the most important global contribution to the overall analysis, especially the humidity sensitive infrared radiances. For the conventional data, the wind measurements of the aircraft and from the geostationary satellites are the most informative. For the targeted area, the data from aircraft and the dropsondes have the largest DFS. It has been noted that the DFS of the dropsondes located in the sensitivity maximum is larger than the other one even if there is no link between the DFS and the forecast. However, the impact of the dropsondes grows with respect to the forecast range and leads to an improvement of the forecast for this case. Copyright © 2006 Royal Meteorological Society [source] Comparing the scores of hydrological ensemble forecasts issued by two different hydrological modelsATMOSPHERIC SCIENCE LETTERS, Issue 2 2010A. Randrianasolo Abstract A comparative analysis is conducted to assess the quality of streamflow forecasts issued by two different modeling conceptualizations of catchment response, both driven by the same weather ensemble prediction system (PEARP Météo-France). The two hydrological modeling approaches are the physically based and distributed hydrometeorological model SIM (Météo-France) and the lumped soil-moisture-accounting type rainfall-runoff model GRP (Cemagref). Discharges are simulated at 211 catchments in France over 17 months. Skill scores are computed for the first 2 days of forecast range. The results suggest good performance of both hydrological models and illustrate the benefit of streamflow data assimilation for ensemble short-term forecasting. Copyright © 2010 Royal Meteorological Society [source] | ||||||||||