"Short-range regional model ensembles for quantitative precipitation forecasting": Jun Du, COMET Postdoctoral Fellow (Environmental Modeling Center)

Final Report

1. Project Objectives and Accomplishments

1.1 Introduction

This SREF project includes the following five objectives:

1. Develop and explore strategies for generating regional-model ensembles and for providing operationally relevant and useful ensemble based products (especially for quantitative precipitation)

2. Test and evaluate methodologies for perturbing initial conditions and models

3. Investigate options with regard to model configuration (e.g. resolution) and ensemble size

4. Develop appropriate tools and procedures for evaluation and validation of ensemble system and products

5. Demonstrate realization of the promise and potential of SREF to provide operationally useful information

The principle investigators of this project are Jun Du and Steve Tracton with invaluable assistance from Zoltan Toth, Henry Juang, Eric Rogers and Perry Shafran.

1.2 Accomplishments in Research and Development

(a) Pilot Study (October 1996 - March 1998)

Major tasks completed

• Introduced regional enhancement of global bred perturbations
• Developed interactive graphical display capability
• Developed basic set of output products
• Developed and applied basic validation tools
• Illustrated significance of uncertainties in SREF
• Demonstrated the potential of SREF to provide operationally useful information
• Provided basis for a prototype operational system

Key findings

• Enhanced diversity of solutions (spread) with
• Multi-model ensemble
• Higher resolution
• Global bred (vs. "random"/different analyses)
• Regional enhancement

(b) Participating in SAMEX (March 1998 - September 1998)

(SAMEX = Storm And Mesoscale Ensemble experiment, http://www.caps.ou.edu/CAPS/samex.html)

Major tasks completed

• Constructed a new prototype SREF system (10-member 32km ETA + RSM with enhanced bred mode)
• Ran and monitored real-time SREF forecasts daily (May 1 - 31)
• Modified and added some new features to the SREF display system and built an SREF web site
• Conducted off-line experiments (lateral boundary condition (LBC) effects and precipitation bombs)
• Developed new tools/procedures for verifying ensemble forecasts against hourly observed precipitation analysis and station sounding data
• Adopted methods for verifying probabilistic forecasts of both basic fields and quantitative precipitation
• Evaluated EMC SAMEX ensemble

Key findings

• Improved ensemble mean skill, spread and full probabilistic information (in terms of reliability and ranked probabilistic skill score, RPSS) with multi-model approach for both basic fields and precipitation.
• LBC plays a very important role for producing ensemble spread if model computation domain is not large enough.
• SAMEX results supported our basic strategy toward building an SREF system.

2. PRESENTATIONS AND PUBLICATIONS

Presentations

1. Evaluation of preliminary results of EMC/NCEP SREF system (the SREF'97 Workshop, Camp Springs, MD, June 1997)

2. Probabilistic forecast of precipitation based on EMC/NCEP SREF system (GCIP conference, Boulder, CO, August, 1997)

3. Applications of SREF to explosive cyclogenesis (the 10th Cyclone Workshop, Montreal, Canada, Sept. 1997)

4. SREF seminar at Atmospheric Environment Service (AES), Canada (Doval, Canada, Sept. 1997)

5. NWS/Office of Meteorology seminar on SREF (Silver Spring, MD, Nov. 1997)

6. EMC Special Seminar on SREF (Camp Springs, MD, Dec. 1997)

7. NCEP SREF system (ECMWF Workshop, the 6th Workshop on Meteorological Operational Systems, Reading, England, Nov. 1997)

8. Short-range ensemble forecasting (SREF) at NCEP/EMC (12th Conf. on Numerical Weather Prediction, Phoenix, AZ, Jan. 1998)

9. Short-range ensemble forecasting (SREF) at NCEP/EMC (XXIIV European Geophysical Society (EGS) General Assembly, Nice, France, April, 1998)

10. SREF seminar at Purdue University (March, 1998)

11. SREF project review seminar at NWS/Office of Meteorology (Silver Spring, MD, March, 1998)

12. SREF seminar at CAPS, University of Oklahoma (April, 1998)

13. SREF at NCEP (Real-time Regional NWP and Verification workshops, MMM/NCAR, Boulder, CO, June 17-19, 1998)

14. SREF at NCEP (MIT science seminar, Sept. 12, 1998)

15. SREF at NCEP (Annual meeting of the Chinese American Oceanographic and Atmospheric Association - COAA, University of Maryland at College Park, College Park, MD, Oct. 24, 1998)

16. SREF project review seminar at NWS/Office of Meteorology (Silver Spring, MD, Nov. 17, 1998)

17. SREF training for forecasters from SPC and other field offices (We provided some of materials and Eugenia Kalnay did the training at Norman, OK, April, 1998)

18. SREF training for forecasters at HPC and other field offices (Steve Tracton, Camp Springs, April 23, 1998)

19. About SREF project -- 6 briefings at NCEP/EMC/Mesoscale Branch (Camp Springs, MD)

Publications

1. Tracton and Du, 1997: SREF at NCEP. Proceedings of the 6th Workshop on Meteorological Operational Systems, Reading, England, Nov. 1997, pp 7)

2. Tracton, Du, Toth and Juang, 1998: Short-range ensemble forecasting (SREF) at NCEP/EMC. Preprints, 12th Conf. on Numerical Weather Prediction, Phoenix, AZ, AMS, 269-272.

3. Tracton and Du, 1998: Short-range ensemble forecasting (SREF) at NCEP/EMC. Research Activities in Atmospheric and Oceanic Modeling (edited by A. Staniforth), Report 27, CAS/JSC Working Group Numerical Experimentation (WGNE), WMO/TD-No. 865, 5.58-5.59.

4. Stensrud, Brooks, Du, Tracton and Rogers, 1998: Using ensembles for short-range forecasting (Mon. Wea. Rev., in press)

5. Du, Tracton, Toth and Juang, 1998: Short-range ensemble forecasting (SREF) at NCEP/EMC (abstract for XXIIV European Geophysical Society [EGS] General Assembly, Nice, France, April, 1998), Physics and Chemistry of the Earth

6. Mullen, Du and Sanders, 1998: The dependence of ensemble dispersion on analysis-forecast system: implication to short-range ensemble forecasting of precipitation (Mon. Wea. Rev., in press)

7. Tracton and Du, 1998: Short-range ensemble forecasting (SREF) at NCEP/EMC. Wea. and Forecasting (in revision)

8. Du, 1998: A review on ensemble forecasting (in Chinese, "Asian Monsoon and Heavy Rain Events in China", Science Press in Beijing, Sept. 1998)

9. Du and Tracton, 1998: Impact of lateral boundary conditions on short-range ensemble forecasting (draft)

10. Evaluation of NCEP/EMC SREF during SAMEX (in preparation)

3. SUMMARY OF BENEFITS

• Directing an operational implementation of an SREF system at NCEP/EMC (SREF I, around Jan. 2000 upon Class VIII computer)
• Providing basis/experience for further development following the SREF I as well as for others in scientific community in general
• Understanding predictability of atmospheric motion especially in mesoscale
• Providing products in ensemble forecasting practice
• Providing verification and validation tools for ensemble system and its products