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SEVERE WEATHER FORECASTS

SEVERE WEATHER FORECASTS. F. Grazzini, F. Lalaurette. - EFI definition and properties - Definition of extreme weather in the observations - EFI Verifications results - A case study - Two new products for severe weather forecasting. OUTLINE. EFI definition.

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SEVERE WEATHER FORECASTS

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  1. SEVERE WEATHER FORECASTS F. Grazzini, F. Lalaurette

  2. - EFI definition and properties - Definition of extreme weather in the observations - EFI Verifications results - A case study - Two new products for severe weather forecasting OUTLINE

  3. EFI definition It is a normalised distance of an ensemble forecast from a climate distribution • 0=forecast distribution identical to the climate one • 1= forecast distribution is a perfect outlier http://www.ecmwf.int/products/forecasts/efi_guide.pdf

  4. EFI: a measure of anomaly and spread Solid lines/current formulation, dashed lines pre 2003 formulation

  5. Climate Atlas of Europe (Météo-France) The atlas contains monthly normals of temperature, precipitation, wind and sunshine duration for ~ 700 selected European stations. In addition statistical information for these parameters and for the occurrence of phenomena such as fog, thunderstorm, hail and snow are reported. The computation period is 1971-2000. More information at http://www.eumetnet.eu.org/ECSN_home.htm EFI verification: the need of a local climatology

  6. Extreme event if 24h TP > Tsh Tsh=max(20,RRQ4/5) RRQ4 = Upper quintile of monthly precipitation (per station, per month) Using GTS synop 2622 “extreme” events were found during the period October 2003 – May 2005 Extreme event definition

  7. Extreme precipitation thresholds

  8. Frequency of extreme daily precipitation TP > Tsh

  9. EFI verification: 221156 total events, 2622 extreme events False Alarm Ratio FAR=F/(H+F) POFD=F/(Z+F)

  10. Verification of prob of TP > 20 mm/24h False Alarm Ratio

  11. Frequency of EFI > 0.6 Medium-Range

  12. Frequency of EFI > 0.45 Medium-Range

  13. Frequency of EFI > 0.6 Short-Range

  14. A case study: heavy precip between 1411 06UTC – 1511 06UTC D+5

  15. A case study D+4

  16. A case study D+3

  17. A case study D+2

  18. New global EFI multi-parameter map for anomalous weather - A simultaneous (synoptic) view of the flow pattern and associated weather parameters can provide a better understanding of possible scenarios. - EFI provides a concise and selective information about deviation of the forecast from the climate http://w3ec2.ecmwf.int/metops/efitest/

  19. Global EFI Map

  20. Global EFI Map D+5

  21. Global EFI Map D+4

  22. Global EFI Map D+3

  23. Global EFI Map D+2

  24. Global EFI Map

  25. Freak wave prediction • It is important to detect possible deviation from linear theory of wave interaction (Gaussian distribution of surface elevation) • In particular condition nonlinear interaction of waves became stronger (focussing). The distribution of surface elevation may deviate from the Normal with increase in probability of anomalous waves (compared to the median) • Additional wave parameters characterizing extreme events have been introduced in to the system in October 2003: BFI and the wave spectra kurtosis

  26. Freak wave prediction: kurtosis analysis

  27. Freak wave prediction: kurtosis analysis

  28. Freak wave prediction: kurtosis forecast T+36

  29. Summary • A step forward towards an EFI validation against observations • Verification could provide useful guidance for calibration • EFI verification for daily precipitation : mixed feelings, however it seem to provide better results than probabilities. • Global multi-parameter EFI maps may be useful to provide a synoptic view of weather anomalies to users • Progress in wind induced ocean freak waves

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