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Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Extended range forecasts at MeteoSwiss: User experience and probabilistic verification ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel, Mark Liniger, Paul Della-Marta, Christof Appenzeller Slide 2 2 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Overview Monthly forecasts WWW: Seasonal forecasts Verification: The RPSS D Comparison: ECMWF vs. other prediction strategies Slide 3 3 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Overview Monthly forecasts WWW: Seasonal forecasts Verification: The RPSS D Comparison: ECMWF vs. other prediction strategies Slide 4 4 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Monthly forecasts 100 % 0 Probability of T 2m to be in lowest tercile Forecast of week 1 Start: 20-04-2006 Slide 5 5 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Monthly forecasts 100 % 0 Probability of T 2m to be in lowest tercile Forecast of week 1 Start: 04-05-2006 Slide 6 6 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Monthly forecasts Probability of T 2m to be in lowest tercile 100 % 0 Forecast of week 1 Start: 11-05-2006 Slide 7 7 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Monthly forecasts Observed anomalies for May What is wrong? Problems to deal with enhanced snow cover?... Slide 8 8 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Overview Monthly forecasts WWW: Seasonal forecasts Verification: The RPSS D Comparison: ECMWF vs. other prediction strategies Slide 9 9 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel WWW: Seasonal forecasts Since winter 2005/06 MeteoSwiss issues an internet bulletin (Climate Outlook) on the upcoming season for Switzerland. Designed to... provide seasonal forecast give background information on methodology point out uncertainties provide climatologic background information Provide common reference for public and media, and avoid dissemination of semi-true information Use seasonal forecasts to promote public interest in other aspects of climate analysis Slide 10 10 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Facts and figures on the summer in Switzerland What do the records show? WWW: Seasonal forecasts Slide 11 11 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Maximum temperature in C Precipitation in mm Average sun shine duration in % WWW: Seasonal forecasts Slide 12 12 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Seasonal forecast current model run. WWW: Seasonal forecasts Slide 13 13 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel WWW: Seasonal forecasts Terciles from station data Slide 14 14 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel What is a seasonal forecast? Methodology WWW: Seasonal forecasts Slide 15 15 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Past seasonal forecasts for Switzerland Verification WWW: Seasonal forecasts Slide 16 16 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel WWW: Seasonal forecasts observation Slide 17 17 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Overview Monthly forecasts WWW: Seasonal forecasts Verification: The RPSS D Comparison: ECMWF vs. other prediction strategies Slide 18 18 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Verification of probabilistic forecasts Real-valued observations Probabilistic forecasts Common approach: Convert observation into probability distribution Ranked Probability Score (RPS) Slide 19 19 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Verification of probabilistic forecasts Real-valued observations Probabilistic forecasts Ensemble predictions But: Ensemble predictions are not truly probabilistic !! Ranked Probability Score (RPS) Slide 20 20 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel 0 100% CDF C N W Example: Three equiprobable categories (e.g. cold, normal, warm) Let the verifying observation fall into the second category Convert real-valued observation into CDF The Ranked Probability Score (RPS) Slide 21 21 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel C N W d 1,EPS d 2,EPS Ensemble prediction system: RPS = d 2 1,EPS + d 2 2,EPS Example: Three equiprobable categories (e.g. cold, normal, warm) Let the verifying observation fall into the second category Compare with CDF of ensemble forecast The Ranked Probability Score (RPS) Slide 22 22 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel C N W 1/3 2/3 1 d 1,Cl d 2,Cl Ensemble prediction system: RPS = d 2 1,EPS + d 2 2,EPS Climatologic forecast: RPS Cl = d 2 1,Cl + d 2 2,Cl Example: Three equiprobable categories (e.g. cold, normal, warm) Let the verifying observation fall into the second category... or with CDF of climatologic forecast The Ranked Probability Score (RPS) Slide 23 23 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel The Ranked Probability Skill Score (RPSS) is defined by relating the RPS of a forecast system with the corresponding RPS of the climatologic reference: The RPSS is negatively biased for small ensemble size ! The RPSS Slide 24 24 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Synthetic random white noise forecasts, verified against random white noise observations. Skill of this forecast system should be zero by definition ! Three equiprobable categories The RPSS Slide 25 25 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Negative bias consequence of inconsistent definition of climatologic reference forecast. Mller et al. 2005, J.Clim. Weigel et al. 2006, Mon. Wea. Rev. The RPSS 1/3 Slide 26 26 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Solution K:Number of forecast categories p i :Prob. of i-th forecast category M:Ensemble size General case Weigel et al. 2006, Mon. Wea. Rev. The RPSS D Slide 27 27 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Special case 1: K equiprobable forecast categories M: Ensemble size Solution The RPSS D Weigel et al. 2006, Mon. Wea. Rev. Slide 28 28 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel Special case 2: Brier score, i.e. two categories with prob p and (1-p) M: Ensemble size Solution Weigel et al. 2006, Mon. Wea. Rev. The RPSS D Slide 29 29 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Forecast Products User Meeting, ECMWF, Reading, UK, 14-16 June 2006 Andreas Weigel The RPSS D Synthetic random white noise forecasts, verified against random white noise observations. Skill of this forecast system should be zero by definition ! Three equiprobable categories Slide 30 30 Extended range forecasts at MeteoSwiss user experience and probabilistic verification ECMWF Fore

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