Mesoscale Numerical Weather Prediction With the WRF Model Ying-Hwa Kuo, Joseph Klemp, and John Michalakes Mesoscale and Microscale Meteorology Division National Center for Atmospheric Research Boulder, Colorado, U.S.A.
3-D Trajectories Anthes’ hurricane simulation 30 x 30 x 3 mesh at 30 km. First 3-D simulation with asymmetric hurricane structure. Slide from Anthes
Modeling Winds in the Columbia Gorge Portland Cascade Locks Troutdale • Strongest winds are at the exit
Weather Research and Forecasting Model Goals: Develop an advanced mesoscale forecast and assimilation system, and accelerate research advances into operations 36h WRF Precip Forecast • Collaborative partnership, principally amongNCAR, NOAA, • DoD, OU/CAPS, FAA, and university community • Governance through multi-agency oversight and • advisory boards • Development conducted by 15 WRF Working Groups • Ongoing active testing and rapidly growing community use • Over 1,600 registered community users, annual • workshops and tutorials for research community • Daily experimental real-time forecasting at NCAR , • NCEP, NSSL, FSL, AFWA, U. of Illinois • Operational implementation at NCEP and AFWA in 2004 Analyzed Precip 27 Sept. 2002
WRF Model Characteristics • Highly modular, single source code with plug-compatible modules • State-of-the-art, transportable, and efficient in a massively parallel • computing environment. • Design priority for high-resolution (nonhydrostatic) applications • Advanced data assimilation systems developed in tandem with the • model itself. • Numerous physics options, tapping into the experience of the full • modeling community. • Maintained and supported as a community mesoscale model to facilitate • broad use in the research community. • Research advances will have a direct path to operations. • With these hallmarks, the WRF model is unique in the • history of numerical weather prediction in the U.S.
Driver Layer Mediation Layer Model Layer 27km WRF Model WRF Parallel Scaling Mobile Bay 150 COMPAC 100 Gflop/s IBM Regatta 50 Intel IBM Winterhawk II 0 0 500 1000 Ocean SST Wave Height processors WRF Software Design • Modular, hierarchical design • Plug compatible physics, dynamical cores • Parallelism on distributed- and shared memory processors • Efficient scaling on foreseeable parallel platforms • Model coupling infrastructure • Integration into new Earth System Model Framework
WRF Version 1.3 12-km CONUS 500 times real time equivalent to 48 h forecast in 6 mins. No I/O or initialization WRF Performance Benchmarks
Key Scientific Questions for Storm-Scale NWP • What is the predictability of storm-scale events, and will resolution of fine-scale details enhance or reduce their prediction? • What observations are most critical, and can high-resolution data (e.g. WSR-88D) from national networks be used to initialize NWP models in real time? • What physics are required, and do we understand it well enough for practical application? • How can ensembles be utilized for storm-scale prediction? • What are the most useful verification techniques for storm and mesoscale forecasts? • What networking and computational infrastructures are needed to support high-resolution NWP? • How can useful decision making information be generated from forecast model output?
Convection-Resolving NWP using WRF Motivating Questions • Is there any increased skill in convection-resolving forecasts, measured objectively or subjectively? • Is there increased value in these forecasts? • If the forecasts are more valuable, are they worth the cost?
10 km WRF forecast domain 4 km WRF forecast domain Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) Goal: Study the lifecycles of mesoscale convective vortices and bow echoes in and around the St. Louis MO area Field program conducted 20 May – 6 July 2003
Real-time WRF 4 km BAMEX Forecast Initialized 00 UTC 9 June 03 Reflectivity forecast Composite NEXRAD Radar
Real-time WRF 4 km BAMEX Forecast Valid 6/10/03 12Z 4 km BAMEX forecast 36 h Reflectivity 4 km BAMEX forecast 12 h Reflectivity Composite NEXRAD Radar
Real-time WRF 4 km BAMEX Forecast Initialized 00 UTC 10 June 03 Reflectivity forecast Composite NEXRAD Radar
Real-time 12 h WRF Reflectivity Forecast Valid 6/10/03 12Z 4 km BAMEX forecast 10 km BAMEX forecast 22 km CONUS forecast Composite NEXRAD Radar
Realtime WRF 4 km BAMEX Forecast Valid 6/23/03 06Z 30 h Reflectivity Forecast Composite NEXRAD Radar 7” hail 00Z Squall line
Real-time WRF 4 km BAMEX Forecast Initialized 00 UTC 12 June 03 Reflectivity forecast Composite NEXRAD Radar
Realtime WRF 4 km BAMEX Forecast Valid 6/12/03 06Z 30 h Reflectivity Forecast Composite NEXRAD Radar Missed
Skill of Storm-scale prediction From Done, Davis and Weisman (2003)
10-km WRF 4-km WRF Parameterized convection (on the 10 km grid) cannot differentiate different mode of convection Dashed magenta indicates approximate area of rainfall Produced by convective parameterization
30h WRF BAMEX Forecast Valid 6/10/03 06Z 4 km Surface Theta-E 10 km Surface Theta-E
30h WRF BAMEX Forecast Valid 6/10/03 06Z 4 km 850 RH 10 km 850 RH
Preliminary BAMEX Forecast Verification Equitable Threat Scores
Preliminary Findings for BAMEX Forecasts • Rapid spinup of storm-scale structure from large-scale IC • Forecasts were helpful to field operations planning, particularly • on the number of systems, their mode and location • 4 km WRF replicates overall MCS structure and character better than 10 km WRF with cumulus parameterization • More detailed representation of convective mode • No improvement in precipitation threat scores • Skill in forecasting systems as high after 21 h as during the • first 6-12 h, suggesting mesoscale control of initiation • Convective trigger function wasn’t needed Convection resolving forecasts should be a useful tool for predicting significant convective outbreaks and severe weather
Challenge: • QPF problematic (too much convective precip) • Stratiform regions appear too small (microphysics?) • Convective systems often fail to decay (BL evolution?) • Lack of convection on high terrain (domain boundary issue?) • Initialization (data assimilation) • Verification methods
WRF Version 2.0 Features • 1-way and 2-way nesting (Multiple domains, flexible ratio) • New physics • Land-surface models (Unified Noah LSM, RUC LSM) • PBL physics (Yonsei Univ PBL) • Microphysics (Hong et al., 3 and 5 classes schemes) • Cumulus (Grell-Devenyi ensemble) • Updated NCEP physics (inc. Betts-Miller-Janjic CPS, • Mellor-Yamada-Janjic PBL, Ferrier microphysics, and • GFDL radiation) • ESMF time-keeping, PHDF5 I/O, and more I/O options • Capability to run WRF initialization program for large domains • Updated Standard Initialization program (nest capability) • Coordinated with WRF 3DVAR release • Optional WRF initialization from MM5 preprocessor (by July) • More complete documentation (users guide & tech note) • V 2.0 release scheduled for June 2004
Auto-Generated On-line Documentation http://www.mmm.ucar.edu/wrf/WG2/software_2.0 • Generated directly from WRF source code • Collapsible/expandable call tree browser • Man-page-style hypertext documentation from in-line code commentary • Clicking a subroutine argument displays trace of variable up call tree to point of definition
WRF and ESMF • WRF is a participating application in ESMF • WRF 2.0 includes ESMF Time Manager • Exact, drift-free time arithmetic, even for fractions of seconds • Time objects in WRF are now compatible with representation in other ESMF-compatible components • Merging of WRF and ESMF I/O specifications in progress • Top level of WRF easily conforms to ESMF component interface for model coupling
For details please refer to http://www.wrf-model.org/ • Upcoming events • WRF workshop: 22-25 June 2004 • WRF Tutorial: 28 June – 2 July 2004