Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Progress in Switzerland Paolo Ambrosetti, MeteoSwiss EMMA Expert Meeting, Helsinki 18 June 2007

2 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (1) Colour assignment criteria within the Meteoalarm intranet will be actualised and fully completed by all individual participants (countries). When a certain colour is missing in the assignment, for one or more of the countries parameters, an explication on the “why” will be added. Main parameters: Wind/Rain/Snow O.K. Thunderstorm: Only yellow level. Forest Fire/Low Temperature/High temperature/Fog will be implemented in Spring 2008 with a new warning software.

3 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (2) The units used within the criteria will be unified on km/hr for wind, cm’s for snow, mm’s for rain. Accumulating time periods within criteria will, if possible, be calculated towards 3, 6 and 24 hrs durations. Units: O.K. Accumulation time periods 3/6/12 hrs added in Intranet.

4 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (3) We should try to harmonise our mean wind and wind gust assignments towards a max windgust criterion in km/hr with only one common defined sample duration factor as a reference (WMO 3sec gust) At MeteoSwiss max wind gust in km/h uses a sample duration factor of 1 second. Experimental studies showed no significant difference with the WMO standard of 3 seconds. Variability among the instruments depends mostly on anemometer inertia.

5 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (4) Area sizes within criteria should be harmonised as much as possible towards 5000km km2 area size makes no sense in a complex orography like Switzerland. For that reason we use 2000 km2 in the northern lowlands and 500 km2 in the Alpine region and on the southern side. Hydrological studies showed a “conversion factor” of about 0.92 in the lowland for an accumulation periods of 24 hours (2000-> 5000 km2), 0.7 in the Alps (500-> 5000 km2). For the southern side it is impossible to calculate a reasonable factor, due to the small size and the very large gradient, particularly in precipitation. (see below)

6 EMMA Helsinki Meeting, P.Ambrosetti Reduction factor for rain accumulation

7 EMMA Helsinki Meeting, P.Ambrosetti Reduction factor for rain accumulation Formula Coefficients are regional dependent

8 EMMA Helsinki Meeting, P.Ambrosetti Reduction factor for rain accumulation

9 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (5) Important: Action will be taken to convert all actual criteria for all the different parameters and colours towards the climatological percentile value (in order to derive the return period). This analysis for each country will be used during our Helsinki meeting !! MeteoSwiss thresholds are essentially based on return period or climatological percentiles with some small smoothing. Only thunderstorm thresholds are based on damage estimates.

10 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (6) Each country will search and communicate examples for special situations on which a combination of factors or derivation of original factors did trigger the damage/impact of the event (for instance freezing rain + windstorm following: Trees are weakened and much more vulnerable). We certainly will learn from these gathered examples. MeteoSwiss currently use some “worsening condition” rules by combination of factors. Examples: Rain + high wind at Geneva lake Rain over saturated or snow covered soil Rain with embedded heavy thurderstorms Snow and high wind in the mountains

11 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (7) To encourage the more frequent use of the Meteoalarm Intranet Forum between operational forecasters, especially during the onset and right after cross boarder severe weather events. By severe weather events operational forecasters are already under great stress and the Meteoalarm Forum is put at lower priority. The participation to the Meteorisk Forum already showed this problem. Nevertheless we will encourage the forecasters at least to look to the Forum in order to motivate them to participate in the future.

12 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (8) Try to involve Civil security within your country to improve colour assignment strategies In 2004 we had a working group on that topic with forecaster, hydrologists, engineers, civil security, insurance specialists. The results were used in the colour assignments and description of possible damages and recommendations to the population

13 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (9) In general: After this return period analysis among all countries has been made for actual criteria (action 3 above) we should aim to relate certain climatological percentiles to a certain colour (for instance red for 0.1% + area 5000km2 and orange 1% + area 5000 km2) At MeteoSwiss some difference to that criteria. See above.

14 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (10) The occurrence of initial severe weather events should preferably be forecasted also in a probabilistic way using probability as a second parameter. This in order for future developments towards a more sophisticated strategy in which risk percentages on threshold exceeding are taken into account to assign the awareness colours. At MeteoSwiss it will be introduced in short time for rain events, wind will come later. Probability values are generated by the LEPS and can be edited by the forecaster. LEPS: ensemble of local model COSMO

15 EMMA Helsinki Meeting, P.Ambrosetti Harmonization issues (10) Probability Medium High Low

16 EMMA Helsinki Meeting, P.Ambrosetti Heat Wave Warning: The warning procedure at MeteoSwiss: - Every day the Heat Index (HI) is computed with the model hourly values of Temperature and RH. The results can be edited by the forecaster. - When the max HI > 90 for 3 consecutive days then a Heat warning is given. - When a warning is active, it will be continued until HI < 90. -We only have a yellow level, because from the climatological records in Switzerland the HI never reach very high values. Reference: