Eidgenössisches Departement des Innern EDI Bundesamt für Meteorologie und Klimatologie MeteoSchweiz New automatic weather type classifications at MeteoSwiss Tanja Weusthoff EMS,

2 Weather type classifications | EMS, Tanja Weusthoff 1. Introduction: New Classifications  The existing manual weather type classifications have been replaced by n ew (automatic) weather type classifications in January OLD NEW Alpenwetterstatistik AWS Perret Zala-Klassifikation manual, until GWT & CAP/PCACA automated, since Januar 2011, recalculated from

3 Weather type classifications | EMS, Tanja Weusthoff 1. Introduction: Cost733 COST 733: “Harmonisation and Applications of Weather Type Classifications for European regions“ ( ) Provides:  Catalogues of classifications calculated for various European domains cost733cat-1 - original classification of the respective author cost733cat recalculated classifications using cost733class software  Software for individual calculations of weather type classifications cost733class Evaluation of catalogue costcat733-1 with regard to the variability of daily precipitation in the Alpine region (Schiemann and Frei, 2010) Selection of suitable weather types for operationalisation in a MeteoSwiss-wide „Beauty Contest“

4 Weather type classifications | EMS, Tanja Weusthoff differentiation convective / advective by means of wind in 500 hPa convective: surface pressure for classification into high, low and flat pressure advective: wind directions using GWT8_Z500 classification classification with predefined types correlation with „prototype“ patterns classification of each input field by means of the three correlation coefficients and their combination main wind directions, high and low pressure STEP 1: Weather types are derived by means of a principal component analysis and subsequent clustering based on ERA40 data. STEP 2: Actual days are assigned to the derived classes by simple distance measures. 1. Introduction: Methods  Overall 10 classifications are calculated each day, based on two different methods using the ECMWF 12 UTC analysis (and forecast) data. 1. CAP = Cluster Analysis of Principal Component 2. GWT = GrossWetterTypes 3. GWTWS = adapted GWT CAP9, CAP18 und CAP27 based on MSL GWT10, GWT18 und GWT26 based on (1) MSL and (2) Z500 GWTWS with 11 classes based on GWT8 for Z500, mean wind in 500 hPa and mean surface pressure

5 Weather type classifications | EMS, Tanja Weusthoff 1. Introduction: Data daily calculation (since ) using 12 UTC run of the operational ECMWF model IFS; analysis and forecasts up to 10 days are classified classifications recalculated using ECMWF reanalysis ERA ERA interim Domain: Alps 41N - 52N (12pts) 3E - 20E (18pts)

6 Weather type classifications | EMS, Tanja Weusthoff Brier Skill Score (BSS) How good can weather type classifications quantify surface climate variability in the Alps? use quantiles to define an event (for each grid box); y i = empirical frequency of the event occuring for weather type i; ō = climatological frequency of a event independant of weather type; perfect forecast: BS perf = 0; reference forecast: y i = ō;  simple form of Brier Skill Score:  consider WTC as a framework that yields a probabilistic forecast (Schiemann und Frei, 2010) 2. Evaluations: BSS BSS shows an increase with the number of classes  compare only weather type classifications with a similar number of classes

7 Weather type classifications | EMS, Tanja Weusthoff daily weather types from 10 automatic and two manual classifications (Schüepp, Perret) gridded daily precipitation data for the Alps, 25 km resolution, (Frei and Schär, 1998; Frei and Schmidli, 2006 ) gridded daily mean temperature, project ENSEMBLES (Haylock et al. 2008), 0.5° resolution, interpolated to the same 25 km grid 2. Evaluations: BSS (data basis)

8 Weather type classifications | EMS, Tanja Weusthoff CAP27 explains precipitation in the Alps best, considering only few classes  CAP9 best rather small differences between the individual classifications 2. Evaluations: BSS (precipitation in the Alps) 26 classes and more18 classes9-11 classesmanual

9 Weather type classifications | EMS, Tanja Weusthoff Clear differences between the classifications, e.g. : GWTxx_Z500 better south of the Alps, GWTxx_MSL better on the alpine ridge and in the north of the Alps, CAP27 best in the western part of the domain. 2. Evaluations: BSS (precipitation in the Alps)

10 Weather type classifications | EMS, Tanja Weusthoff larger differences between individual classifications CAP27 explains variability of temperature best when the whole year is considered considering only few classes  CAP9 best 2. Evaluations: BSS (temperature in the Alps) 26 classes and more18 classes9-11 classesmanual

11 Weather type classifications | EMS, Tanja Weusthoff … Schüepp better in individual seasons, especially in summer 26 classes and more18 classes9-11 classesmanual 2. Evaluations: BSS (temperature in the Alps)

12 Weather type classifications | EMS, Tanja Weusthoff clear differences between the classifications, e.g.: GWTxx_Z500 better on the Alpine ridge, GWTxx_MSL and CAP better in the north of the Alps, Schüepp clearly better in summer. 2. Evaluations: BSS (temperature in the Alps)

13 Weather type classifications | EMS, Tanja Weusthoff No influence on precipitation results. Large influence on temperature results. SP = mean sea level pressure Z5 = 500hPa geopotential height Y5 = 500hPa geopotential height K5 = thickness between 500 hPa and 850 hPa 26 classes and more 18 classes 9-11 classes manual 2 input parameters 3 and more input parameters precipitationtemperature 2. Evaluations: BSS (additional input parameters)  cost733cat-2.0

14 Weather type classifications | EMS, Tanja Weusthoff 3. Summary 10 new weather type classifications introduced at MeteoSwiss all weather types available from Description and a report available on MeteoSwiss Websites the best suited weather type classification depends on the respective application already in use for various applications (e.g. verification, climate analyses, …)

15 Weather type classifications | EMS, Tanja Weusthoff standard_produkte/wetterlagenklassifizierung.html Report Weusthoff, T., 2011: Weather Type Classification at MeteoSwiss – Introduction of new automatic classifications schemes, Arbeitsberichte der MeteoSchweiz, 235, 46 pp. Thank you for the attention...