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Analisi modellistica di un evento estremo: 3-4 Novembre 1966

Analisi modellistica di un evento estremo: 3-4 Novembre 1966. Risultati preliminari dal progetto congiunto Flood 66 tra: ECMWF ( R. Buizza, S. Uppala, E. Klinker), ISAC-CNR (A. Buzzi, P.Malguzzi), Università di Brescia, Dip. Ing. Civile (G. Grossi, R. Ranzi, B. Bacchi). FLOOD 66.

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Analisi modellistica di un evento estremo: 3-4 Novembre 1966

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  1. Analisi modellistica di un evento estremo: 3-4 Novembre 1966 Risultati preliminari dal progetto congiunto Flood 66 tra: ECMWF (R. Buizza, S. Uppala, E. Klinker), ISAC-CNR (A. Buzzi, P.Malguzzi), Università di Brescia, Dip. Ing. Civile (G. Grossi, R. Ranzi, B. Bacchi)

  2. FLOOD 66 Grosseto Major widespread hystoricalstorm and flood event, which caused disasters mainly in Tuscany (Florence, Grosseto and other towns) and in other parts of central and north-eastern Italy, such as Venice (highest tide on record), Trento and in many valleys situated in Veneto and Friuli, in Eastern Alps, Emilia etc. in the period 3-5 November. Venezia Firenze Dolomiti bellunesi

  3. Objectives: • Use the ERA database to analayze the extreme event and to assess the value of the ERA-40 for a-posteriori studies of the ECMWF forecasting system value for weather risk assessment. • Examine the accuracy of deterministic and probabilistic forecasts during the period of the 1966 flood in Florence and in the Eastern Alps • Investigatethe possibility of using forecasts to drive river-basin discharge hydrological models using direct model output from a meteorological model chain, including hydrostatic and non-hydrostatic, cloud-resolving models.

  4. Tuscany (Arno and Ombrone River basins) 200 • extreme event for precipitation intensity, extension and continuity – most of the rain fell on 4 November 200 200 400 300

  5. The Eastern Alps (Adige and other river basins) 250 Most of precip. fell 3-4 November) 500 400 700 250 500 400

  6. Z500 TL511L60 analysis: 12 UTC of 1-4 November This figure shows the TL511L60 analyses at 12UTC of 1-4 November. Contour interval is 4dam.

  7. ERA40 and TL511L60 analyses: 12 UTC of 1-2 November The ERA-40 (TL159L60, left) and the TL511L60 (right) analyses at 12UTC of 1 and 2 November are very similar (ci is 2dam for full fields and 1dam for difference).

  8. MSLP, 4 Nov. 1966, 00 and 12 UTC. ECMWF ERA-40 special high-resolution (TL511L60), interpolated on the BOLAM grid

  9. 950 hPa wind, 4 Nov. 1966, 00 and 12 UTC. ECMWF ERA-40 special high-resolution (TL511L60), interpolated on the BOLAM grid

  10. 500 hPa wind, 4 Nov. 1966, 00 and 12 UTC. ECMWF ERA-40 special high-resolution (TL511L60), interpolated on the BOLAM grid

  11. 24h TP: ECMWF TL511L60 deterministic forecasts for 3-4 Nov (168h, 120h, 72h) t+96-120h t+144-168h This figure shows TL511L60 forecasts of 24h-accumulated precipitation started at 12UTC of the 27 (144-168h) and 29 (96-120h) October, and 1 November (48-72h) and valid for 3-4 November. The right-bottom panel shows a proxi for verification defined by the TL511L60 24h forecast started at 12UTC of 3 November. Contour isolines are 2-25-50-75-100-150-300 mm for precipitation. 3-4 Nov t+48-72h

  12. 24h TP: EPS fc from 30 Oct for 3-4 Nov (96-120h) P(TP>50mm) P(TP>25mm) This figure shows three EPS (51*TL255L40) probabilistic forecasts started on 30 October (96-120h) and valid for 3-4 November, for 24-h accumulated precipitation in excess of 25, 50 and 75 mm. The right-bottom panel shows a proxi for verification given by the TL511L40 24h forecast started on 3 November. Contour isolines are 2-10-20-40-60-100% for probabilities and 2-25-50-75-100-150-300 mm for precipitation. P(TP>75mm) 3-4 Nov Good EPS t+96-120h fc over Friuli for all thresholds, and some signals that 75mm could hit also Tuscany …

  13. 24h TP: EPS fc from 31 Oct for 3-4 Nov (72-96h) P(TP>25mm) P(TP>50mm) This figure shows three EPS (51*TL255L40) probabilistic forecasts started on 31 October (72-96h) and valid for 3-4 November, for 24-h accumulated precipitation in excess of 25, 50 and 75 mm. The right-bottom panel shows a proxi for verification given by the TL511L40 24h forecast started on 3 November. Contour isolines are 2-10-20-40-60-100% for probabilities and 2-25-50-75-100-150-300 mm for precipitation. 3-4 Nov P(TP>75mm) EPS t+72-96h fc does not propagate quickly enough, but there is a stronger signal that 75mm could hit also Tuscany … Compared to previous fc, consistent but delayed signal, with more localized probability values ..

  14. P(TP>25mm) P(TP>50mm) 24h TP: EPS fc from 1 Nov for 3-4 Nov (48-72h) This figure shows three EPS (51*TL255L40) probabilistic forecasts started on 30 October (96-120h) and valid for 3-4 November, for 24-h accumulated precipitation in excess of 25, 50 and 75 mm. The right-bottom panel shows a proxi for verification given by the TL511L40 24h forecast started on 3 November. Contour isolines are 2-10-20-40-60-100% for probabilities and 2-25-50-75-100-150-300 mm for precipitation. P(TP>75mm) 3-4 Nov Good EPS t+48-72h fc for all thresholds …Compared to previous fc, consistent but with higher and correctly localized probability values ..

  15. Rianalisi ECMWF (60 km) Rianalisi ECMWF (60 km) BOLAM 18 km BOLAM 18 km 2 nov 2 nov 3 nov 3 nov 4 nov 4 nov 5 nov 5 nov 12 UTC 1 Nov 66 12 UTC 1 Nov 66 06 UTC 5 Nov 06 UTC 5 Nov BOLAM 6 km BOLAM 6 km 00 UTC 2 Nov 00 UTC 2 Nov MOLOCH 2 km MOLOCH 2 km 00 UTC 3 Nov 00 UTC 3 Nov Accumulated precipitation period Accumulated precipitation period 06 UTC 3 Nov 06 UTC 3 Nov Rianalisi ECMWF (T511, 45 km) BOLAM 18 4 nov 3 nov 5 nov 2 nov 12 UTC 1 Nov 66 06 UTC 5 Nov BOLAM 6 km 00 UTC 2 Nov MOLOCH 2 km 00 UTC 3 Nov Accumulated precipitation period 06 UTC 3 Nov

  16. The BOLAM 6km precipitation forecast

  17. The MOLOCH 2 km precipitation forecast

  18. The MOLOCH 2 km precipitation forecast

  19. The MOLOCH 2 km precipitation forecast but starting with the NCEP reanalysis (300 km!)

  20. ECMWF NCEP Short digression about ECMWF vs NCEP reanalyses …

  21. ECMWF NCEP

  22. ECMWF NCEP

  23. ECMWF NCEP

  24. Case with flattened orography : stronger cyclone, slightly weaker LLJ and much weaker precipitation (a 24 hour FC) Some sensitivity experiments: role of orography and sea surface fluxes…

  25. Some sensitivity experiments: role of orography and sea surface fluxes… Reference case: a 24 hour FC

  26. Accumulated precipitation with different sea surface fluxes … Case with different surface fluxes No sens. lat. heat fluxes Reference SST + 3 K

  27. Simulazioni idrologiche Isarco a Chiusa A=3059 km² Adige a Bronzolo A=6926 km² Avisio a Lavis A=934 km² Adige a Trento A=9763 km² Noce a S.Giustina A=1050 km²

  28. Esempio di risultato della modellistica idrologica (Univ. di Brescia)

  29. Conclusioni • L’evento viene ‘ricostruito’ in maniera realistica, nonostante le incertezze nelle analisi e le notevoli differenze tra l’analisi NCEP e quella ECMWF, probabilmente associate alle incertezze sull’Atlantico. • Sorprende la possibilità di ricostruire campi di precipitazione dettagliati a partire dalle analisi NCEP, persino meglio che con le analisi ECMWF. • L’origine appare nelle scale grandi (crescita di un’onda baroclina, associata a jet meridionale e intensa frontogenesi) • Nonostante questo, la predicibilità appare bassa prima di 3 giorni: la natura ‘estrema’ dell’evento non appare ad un orizzonte > 2-3 gg. • Precipitazione orografica sulle Alpi, apparentemente convettiva sull’Italia centrale, quest’ultima predicibile solo con il modello non idrostatico. • L’orografia determina totalmente la distribuzione della precipitazione ‘orografica’ e la ciclogenesi; i flussi superficiali sono relativamente poco importanti.

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