Deutscher Wetterdienst Preliminary evaluation and verification of the pre-operational COSMO-DE Ensemble Prediction System Susanne Theis Christoph Gebhardt, Zied Ben Bouallègue, Carlos Peralta, Michael Buchhold

EMS – September 2011 Presentation Overview  Setup of COSMO-DE-EPS  First results of pre-operational phase  Objective verification  Forecasters‘ feedback; evaluation of case studies

Deutscher Wetterdienst Setup of COSMO-DE-EPS

EMS – September 2011 COSMO-DE-EPS status  pre-operational phase has started: Dec 9 th, 2010  pre-operational setup:  20 members (upgrade to 40 member in 2012)  grid size: 2.8 km convection-permitting  lead time: 0-21 hours, 8 starts per day (00, 03, 06,... UTC)  variations in physics, initial conditions, lateral boundaries model domain

EMS – September 2011 Generation of Ensemble Members “multi-configuration” different configurations of COSMO-DE model Variations in Forecast System for the Representation of Forecast Uncertainty Initial Conditions BoundariesModel Physics “multi-model” driven by different global models “multi-model” COSMO-DE initial conditions modified by different global models

EMS – September 2011 Generation of Ensemble Members COSMO-DE-EPS 2.8km COSMO 7km plus variations of initial conditions model physics BC-EPS GME, IFS, GFS, GSM Ensemble Chain

Deutscher Wetterdienst First Results of Pre-operational Phase - Objective verification - Forecasters‘ feedback; Evaluation of case studies

EMS – September 2011 Focus on precipitation  Ensemble Members  Probabilities of Precipitation SYNOP RADAR Verification

EMS – September 2011 PREC 1h accumulation Do the ensemble members have different long-term statistics? (multi-model / multi- configuration) Are there many cases with the same „best member“ or „wettest member“? Only small differences in long-term statistics  Members may be treated as equally probable Only small differences in long-term statistics  Members may be treated as equally probable DETERMINISTIC SCORES for Individual Members } 20 members Forecast Time [h] IFS GME GFS GSM Equitable Threat Score JUNE 2011 FBI threshold 1 mm threshold 0.1 mm

EMS – September 2011 PREC 1h accumulation How well does the ensemble spread of the forecast represent the true variability of the observation? RANK HISTOGRAM a) Underdispersiveness relatively small b) Four groups  Many cases with large influence by global models a) Underdispersiveness relatively small b) Four groups  Many cases with large influence by global models Frequency JANUARY 2011 Rank JUNE 2011 Rank Frequency

EMS – September 2011 PREC 1h accumulation How good are the probabilities derived from the ensemble? compared to the deterministic COSMO-DE (always forecasting 0% or 100%) Look at Brier Skill Score (no skill: zero) - for different precipitation thresholds (colors) (probabilites of exceeding a certain threshold) - for different forecast lead times (x-axis) BRIER SKILL SCORE Always positive!  Ensemble provides additional value to COSMO-DE Additional value grows with lead time (less deterministic predictability) Always positive!  Ensemble provides additional value to COSMO-DE Additional value grows with lead time (less deterministic predictability) JANUARY Forecast Time [h] > 0.1 mm > 1 mm > 2 mm

EMS – September 2011 PREC 1h accumulation How good are the probabilities derived from the ensemble? compared to the deterministic COSMO-DE (always forecasting 0% or 100%) Look at Brier Skill Score (no skill: zero) - for different precipitation thresholds (colors) (probabilites of exceeding a certain threshold) - for different forecast lead times (x-axis) BRIER SKILL SCORE Always positive!  Ensemble provides additional value to COSMO-DE Additional value grows with lead time (less deterministic predictability) Always positive!  Ensemble provides additional value to COSMO-DE Additional value grows with lead time (less deterministic predictability) JUNE Forecast Time [h] > 0.1 mm > 1 mm > 2 mm

EMS – September 2011 PREC 1h accumulation How good are the probabilities derived from the ensemble? compared to the deterministic COSMO-DE (always forecasting 0% or 100%) Look at Brier Skill Score (no skill: zero) - for different precipitation thresholds (x-axis) (probabilites of exceeding a certain threshold) - for all foreast lead times BRIER SKILL SCORE For larger precipitation amounts (summer): even more additional value For larger precipitation amounts (summer): even more additional value MAY - JULY Threshold [mm/h]

EMS – September 2011 PREC 1h accumulation RELIABILITY DIAGRAM Reliability diagram shows some bias and underdispersiveness Lines are sloped  additional calibration has good potential Reliability diagram shows some bias and underdispersiveness Lines are sloped  additional calibration has good potential log (# fcst) > 0.1 mm > 1 mm > 2 mm JUNE 2011 Are the probabilities already well calibrated? (without extra calibration) If we isolate all cases with a forecast probability of -say % … did the event occur in 80% of these cases? diagonal line: optimal - for different prec thresholds (colors) (probs of exceeding a threshold)

EMS – September 2011  Ensemble provides additional value to COSMO-DE (for all accumulations, lead times, precipitation thresholds,…)  Ensemble underdispersiveness is relatively small  Ensemble members may be treated as equally probable  Additional calibration has good potential Pre-operational COSMO-DE ensemble prediction system already meets fundamental quality requirements for precipitation Pre-operational COSMO-DE ensemble prediction system already meets fundamental quality requirements for precipitation Summary of Verification (Precipitation)

EMS – September 2011 Other Variables  T_2M and VMAX have been verified  ensemble spread is far too small COSMO-DE ensemble prediction system has been developed with focus on precipitation COSMO-DE ensemble prediction system has been developed with focus on precipitation Upgrade to 40 members will also look at other variables V_MAX 10m Jan./Feb./ Mar.  nevertheless, ensemble provides additional value to COSMO-DE

First Results of Pre-operational Phase - verification - forecasters‘ feedback; evaluation of case studies

Observation: 12h-precip, 18 UTC, Synop and Radar Severe weather Rostock

EMS – September Rostock (2) COSMO-DE: 12h-precip Synop: 18 UTC, 12h precip COSMO-DE 00 UTC + 18 h Synop: 18 UTC, 12h precip COSMO-DE 06 UTC + 12 h

EMS – September UTC-run (previous day) +21h 00 UTC-run UTC-run +15 COSMO-DE-EPS: Prob > 25 mm, 12h-RR UTC Good consistency of successive model runs Rostock (3)

EMS – September UTC-Lauf (Vortag) +21h 00 UTC-Lauf UTC-Lauf +15 COSMO-DE-EPS: Prob > 40 mm, 12h-RR UTC Probabilities provide good information on location and intensity of the event Rostock (4)

EMS – September h-prec, SRNWP PEPS 00+18h 12h-prec, COSMO-DE-EPS 00+18h Rostock (2) Prob > 40 mm, 12h-prec UTC COSMO-DE-EPS is able to capture heavy convective precip events provides optimal guidance for forecasters (in this case) COSMO-DE-EPS is able to capture heavy convective precip events provides optimal guidance for forecasters (in this case)

EMS – September , 06 UTC 1h precip [mm/h] Synop Radar : Severe storm Bremen , 06 UTC 1h precip [mm/h] Synop COSMO-DE deterministic 21 UTC + 09 h Forecaster: Where to expect the main shower activity and what will be maximum intensity?

EMS – September 2011 Synop 06 UTC, 1h precip C-EPS upscaled prob >15mm 18 UTC + 12 h Synop 06 UTC, 1h precip C-EPS Max of all members 18 UTC + 12 h Probability defines area of occurrence Maxmem (or 90% quantile) provides estimation of possible intensities : Bremen (2)

EMS – September : cold front NRW Radar and Synop: 19 UTC, 1h precip COSMO-DE deterministic 12 UTC + 07 h Large location error in C-DE, horizontal extent of severe precip. too small

EMS – September : cold front NRW (2) Radar, Synop: 19 UTC, 1h precip C-DE-EPS upscaled Prob >15mm/h 12 UTC + 7 h Radar, Synop: 19 UTC, 1h precip C-DE-EPS Perc90% 12 UTC + 7 h C-DE-EPS: better localization and intensity estimation But: BC-EPS does not adequately capture uncertainty on synoptic scale C-DE-EPS: better localization and intensity estimation But: BC-EPS does not adequately capture uncertainty on synoptic scale

EMS – September : severe storm Frankfurt Radar 19 UTC, 1h precip Synop 19 UTC, max wind (1h) COSMO-DE max wind (1h), 09 UTC + 08 h Synop 19 UTC, max wind (1h) C-DE determ. run: no indication of gale-force winds (fx>29 m/s)

EMS – September : Frankfurt (2) C-EPS 90%quant max wind (1h), 06 UTC + 11 h Synop 19 UTC, max wind (1h) C-EPS maxwind prob > 29m/s 06 UTC + 11 h Synop 19 UTC, max wind (1h) C-DE -EPS: clear signals for gale-force winds above 29 m/s. Useful guidance for forecasters despite of timing error

EMS – September 2011 Forecasters‘ Feedback  what they prefer to use:  90%-quantile or maximum of all members of precipitation  precipitation probabilities for an area (10x10 grid points)  what they appreciate:  early signals for heavy precipitation  indication that deterministic run may be wrong  what they criticize:  jumpiness between subsequent runs  lack of spread in T_2M and VMAX  what they are learning:  dealing with low probabilities (10% probability for extreme weather  issue a warning?)

EMS – September 2011

Generation of Ensemble Members Perturbation Methods Peralta, C., Ben Bouallègue, Z., Theis, S.E., Gebhardt, C. and M. Buchhold, 2011: Accounting for initial condition uncertainties in COSMO-DE-EPS. Submitted to Journal of Geophysical Research. Peralta, C. and M. Buchhold, 2011: Initial condition perturbations for the COSMO-DE-EPS, COSMO Newsletter 11, 115–123. Gebhardt, C., Theis, S.E., Paulat, M. and Z. Ben Bouallègue, 2011: Uncertainties in COSMO-DE precipitation forecasts introduced by model perturbations and variation of lateral boundaries. Atmospheric Research 100, (contains status of 2009)

EMS – September : Thunderstorm München C-EPS upscal prob > 10mm, 00 UTC + 21 h Synop 21 UTC, 1h precip C-DE -EPS: 21 and 12h probability forecasts provide useful information on the storm C-EPS upscal prob > 10mm, 00 UTC + 12 h

EMS – September 2011 C-EPS upscal prob > 10mm, 12 UTC + 09 h Synop 21 UTC, 1h precip C-EPS upscal prob > 10mm, 15 UTC + 06 h C-DE -EPS: Event lost in forecast 12 UTC+9h. Jumpiness of successive runs is a problem! C-DE -EPS: Event lost in forecast 12 UTC+9h. Jumpiness of successive runs is a problem!

EMS – September 2011 COSMO-DE-EPS plans ( )  upgrade to 40 members, redesign  statistical postprocessing  initial conditions by LETKF  lateral boundary conditions by ICON EPS reach operational status 2013