Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Probabilities from COSMO-2 derived with the neighborhood method COSMO General Meeting 18 – 21 September 2007 Athens, Greece Pirmin Kaufmann, MeteoSwiss

2 COSMO General Meeting 2007, Athens, Greece (presented by Neighborhood method Probabilistic forecast from deterministic model Represents probability related to local-scale spatial and temporal model uncertainty and predictability Important especially on small scales (e.g. thunderstorms) Method does not represent uncertainty in synoptic forcing (complement to, not substitute for EPS)

3 COSMO General Meeting 2007, Athens, Greece (presented by Original shape of the neighborhood Ellipsoidal Original shape of Theis et al. (2005) Spatial radius decreases with increasing distance in time: Space-time dependency x y t

4 COSMO General Meeting 2007, Athens, Greece (presented by Shape of the neighborhood Cylindrical Assuming spatial and temporal uncertainty are independent True in weak ambient winds, not true for strong ambient winds Equal weights for all grid poins x y t

5 COSMO General Meeting 2007, Athens, Greece (presented by Linearly fading weights Problem: Circles around singular high model values Idea: Smooth edges Introduce linear fading of weights (similar to relaxation) Adds sponge layer around cylindrical neighborhood Large, medium, small neighborhood

Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Cases from „Windbank“ Simulations 1995 – 1999 Threshold 35 mm / 12 h

7 COSMO General Meeting 2007, Athens, Greece (presented by (Case A) Temporal radius r t =6r t =3 r t =1obs

8 COSMO General Meeting 2007, Athens, Greece (presented by (Case A) Spatial radius r xy =15r xy =10 r xy =5obs

9 COSMO General Meeting 2007, Athens, Greece (presented by (Case E) Temporal radius r t =6r t =3 r t =1obs

10 COSMO General Meeting 2007, Athens, Greece (presented by (Case E) Spatial radius r xy =15r xy =10 r xy =5obs

11 COSMO General Meeting 2007, Athens, Greece (presented by (Case L) Temporal radius r t =3 obsr t =1 r t =6

12 COSMO General Meeting 2007, Athens, Greece (presented by (Case L) Spatial radius obsr xy =5 r xy =15r xy =10

13 COSMO General Meeting 2007, Athens, Greece (presented by Recent case: 8/9 August 2007 Flood

14 COSMO General Meeting 2007, Athens, Greece (presented by Objective probabilistic verification Verification needs to be done, but can it be done? High density rain gauge network: Only 24 h resolution Network with 10 min rainfall data: Only coarse spatial resolution Optimal radius: Quality measure (e.g. BSS) increases with increasing radius, „an optimal neighborhood size cannot be found at all“ (experience of S. Theis; Theis 2005) Result for 7 km COSMO resolution -> still valid at 2 km ? Sparseness of data: Extreme precipitation occurs only in few cases is often limited in spatial extent

15 COSMO General Meeting 2007, Athens, Greece (presented by Neighborhood method Main influence is spatial radius r xy and fading zone r f. Only minor changes with temporal radius r t. Consequence of accumulated precipitation values Should we treat the time dimension differently altogether? -> Maximum over time Current settings at MeteoSwiss (precipitation): COSMO-2: r xy =15, r f =15, r t =3 COSMO-7: r xy = 5, r f = 5, r t =3 Need of high resolution data for verification: Resolution of rain gauges insufficient, either spatial or temporal THE END