1. Proposed Predictability, Dynamics & Ensemble Forecasting Expert Team Richard Swinbank, with Heini Wernli, Masayuki Kyouda and Istvan Szunyogh, and thanks to other WG members Joint THORPEX-ICSC & WWRP-JSC meetings, Geneva, July 2013

2. Contents  Current scope of GIFS-TIGGE and PDP working groups  Proposed new expert team / working group  Scientific linkages between dynamical processes, predictability and ensemble forecasting.  The group’s role within new WWRP structure

3. TIGGE – Research focus The TIGGE project (& GIFS-TIGGE working group) was originally focused on the technical work enabling the establishment of the TIGGE archive dataset. The main scientific aspects of THORPEX were covered by Predictability & Dynamical Processes WG, and also Data Assimilation & Observing Systems WG(s). Following the successful establishment of the TIGGE dataset, the focus of the GIFS-TIGGE working group has shifted towards research on ensemble forecasting. Particular topics of interest include:  a posteriori calibration of ensemble forecasts;  combination of ensembles produced by multiple models;  research on and development of probabilistic forecast products. More recently, we have broadened our range of interest to cover improvement of EPSs, including:  representing uncertainties in initial conditions  stochastic physics & other techniques to account for model error

4. PDP group - scope  Since its inception, the PDP working group has covered many aspects of predictability and dynamical processes,  … including the theoretical basis of ensemble forecasting.  The group brings together experts from both academia and operational NWP centres, to accelerate the transfer of cutting-edge science to operational weather forecasting.  It encourages the research community to carry out studies to improve the understanding of the relationship between particular dynamical processes and weather forecast accuracy.

5. Virtuous Circle Develop, Improve Evaluate, Diagnose Ensemble Forecasts To improve EPSs we need to develop a virtuous circle – best with a single group with focus on ensemble prediction

6. Looking forward - A proposed new working group  The logical evolution of the THORPEX working groups would be the creation of a Predictability Dynamics & Ensemble Forecasting working group, combining elements of the current GIFS-TIGGE and PDP groups.  This new group would provide a centre of scientific expertise on dynamics, predictability and ensemble forecasting that is currently lacking in the core WWRP programme.

7. Triangular relationship Dynamical Processes Predictability Ensemble Forecasting There are strong links between the three elements of the proposed group

8. Typhoon Malakas case study  The connections between predictability, dynamics and ensemble forecasting is illustrated by “Predictability of the Tropical Cyclone–Extratropical Flow Interaction Associated with Typhoon Malakas (2010) and Resulting High-Impact Weather Downstream” by Archambault et al (DACA-13) Typhoon outflow ET transition at 0 UTC 25 th Sept

9. GFS ensemble forecast of Rossby wave train Ensemble members Ensemble mean Analysis 0000 UTC 20 Sep initialization 340-K isentrope on the dynamic tropopause (2-PVU surface) Verifying 0000 UTC 25 Sep 120-h forecast T+0 h With thanks to Heather Archambault

10. GFS ensemble forecast of Rossby wave train Ensemble members Ensemble mean Analysis 0000 UTC 20 Sep initialization 340-K isentrope on the dynamic tropopause (2-PVU surface) Verifying 0000 UTC 27 Sep 168-h forecast T+48 h With thanks to Heather Archambault

11. GFS ensemble forecast of TC–extratropical flow interaction (T+0 h) Ensemble members Ensemble mean Analysis MSLP of 945 hPa 0000 UTC 20 Sep initialization Verifying 0000 UTC 25 Sep 340-K isentrope on the dynamic tropopause (2-PVU surface) With thanks to Heather Archambault

12. GFS ensemble forecast of TC–extratropical flow interaction (T+0 h) Ensemble members Ensemble mean Analysis 1000-hPa MSLP contours TC is too weak and too far east in forecasts 0000 UTC 20 Sep initialization Verifying 0000 UTC 25 Sep 340-K isentrope on the dynamic tropopause (2-PVU surface) MSLP of 945 hPa With thanks to Heather Archambault

13. Ensemble members Ensemble mean Analysis 0000 UTC 20 Sep initialization 340-K isentrope on the dynamic tropopause (2-PVU surface) Verifying 0000 UTC 25 Sep ECMWF ensemble forecast of Rossby wave train 120-h forecast T+0 h With thanks to Heather Archambault

14. Ensemble members Ensemble mean Analysis 0000 UTC 20 Sep initialization 340-K isentrope on the dynamic tropopause (2-PVU surface) Verifying 0000 UTC 27 Sep ECMWF ensemble forecast of Rossby wave train 168-h forecast T+48 h With thanks to Heather Archambault

15. 15 WWRP structure and links to WCRP 15

16. Scope of new Projects focused on key “hot spots” Time scale Space scale S2S HIW PPP WWRP domain …while expert teams should cover the entire domain

17. Role  Foster scientific research on dynamics, predictability and ensemble forecasting  Support for WWRP projects PPP, S2S, HIW, FDPs, RDPs  Bridge between academic & operational communities  Steering development of ensemble prediction databases (TIGGE and TIGGE-LAM) to support scientific research  Promote use of EPS datasets by the research community

18. Scientific Scope  Centre of expertise on dynamical processes, predictability and ensemble forecasting.  Understanding & improving probabilistic predictive skill, and its links with dynamical phenomena  Scientific issues include  Growth & evolution of errors  Stochastic representation of unresolved processes  Covering short- to medium-range forecast timescales (potentially longer)

19. Relationship with other teams / groups  There are clear linkages with WGNE and other WWRP expert teams.  Numerical modelling,  Ensembles,  Data assimilation,  Stochastic parameterization and  Evaluation …are all closely linked on both weather and climate timescales.  Too big for a single expert team or working group – we need a set of more specialised teams…  providing expert support to WWRP projects (S2S, PPP, HIW, RDPs & FDPs)

20. Other issues Current GIFS-TIGGE roles  Development of severe weather products  Would fit well into scope of proposed HIW project.  Technical management of data archives:  On-going maintenance should be continued through liaison between archive centres & data providers via email;  Management should be overseen by PDEF team. Representative of archive centre on ET. Current PDP roles  Treatment of systematic model errors  Would be subsumed in WGNE.

21. Next Steps  Provided that this meeting agrees that the proposed expert team (/working group) is the best way forward…  Approval will be required by CAS (Nov 2013) & WMO- EC (Spring 2014).  Transition arrangements  Arrange joint PDP/GIFS-TIGGE meeting in early 2014, to agree detailed scope & responsibilities of the expert team.  Work towards merger of GIFS-TIGGE and PDP groups at end of 2014  New members of both groups chosen for role in new team.