1. NOAA/NWS Change to WRF 13 June 2006

2. What’s Happening? WRF replaces the eta as the NAM –NAM is the North American Mesoscale “timeslot” or “Model Run” at NOAA/NWS’s National Center for Environmental Prediction (NCEP). –NMM is not a MODEL ! –A version of WRF is replacing eta as the model run at NCEP in the NMM timeslot.

3. What is WRF ? WRF is Weather Research and Forecasting Model. WRF is a “infrastructure” system to conduct Numerical Weather Prediction. –This includes analysis, prediction, post- processing and verification WRF is a “community” system that allows easier transition of research into operations

4. WRF is not a “model” WRF is configurable in hundreds of different ways. It is not a single model. Two (2) “Cores” –NMM –ARW Variety of “Physics” to handle meso and micro scale processes related to Convection and the Boundary Layer.

5. Initial Conditions New Analysis System Getting the starting point correct is critical to getting the forecast correct. Minor and “non-observable” initial errors lead to erroneous forecast Grid Point Statistical Interpolation (GSI) is used for the NCEP NMM-WRF.

6. GSI – What’s New? Improved first guess and balance with observations. Improved handling of moisture by allowing temperature and satellite radiances to affect the first guess. At least initially, precipitation effects (from observations and radar) are not being used (they were for the eta).

7. GSI – What’s New? Changes in GSI include: –4 km Snow Analysis (was 24 km) –~5 NM Sea Surface Temperature Analysis (was 30 NM) –Addition on GPS Precipitable Water Sensors.

8. New Snow Cover Analysis

9. What’s Different About WRF? The Vertical Coordinate System –Eta had a “Stepped” vertical coordinate system –WRF uses a hybrid sigma – or terrain following. Higher Resolution at High Terrain More Resolution in the Stratosphere

10. The Vertical Coordinate Systems

11. Terrain Because of the sigma coordinate system, terrain is more realistic in WRF

12. Terrain in the Northeast http://www.meted.ucar.edu/nwp/pcu2/wrftopo/topocompare.htm

13. The WRF-NAM is non-hydrostatic! What Does this mean? Vertical Motions are handled differently – they’re explicitly predicted in the non- hydrostatic version. Stronger and More Details in the Vertical Motion Fields. Important where there’s strong forcing –Mountain Waves –MCS or explosive cyclogenesis.

14. What to expect from the non- hydrostatic WRF? Look for more intense and detailed omega in the NAM-WRF Different and more intense mountain waves. Waves throughout the troposphere Changes to wind fields.

15. What’s Not Changed Horizontal Resolution – 12 km Domain is the same Physics –Convective Parameterization –Planetary Boundary Layer

16. Model Output Statistics (MOS) None eta based MOS will continue until the end of the year from a special low resolution (32 km) version of eta.

17. What else to expect? Improved details in high terrain compared to eta. –Primarily West Coast, but do expect differences in even small terrain Noisier fields. –Small feature will not be “damped” out like they were in the eta.

18. Problems? Heavier Precipitation Explosive Cyclogenesis

19. Heavier Precipitation While WRF has same convective scheme as eta, but non-hydrostatic effect can result in significant additional amounts in the QPF Field.

20. Extra Convective Precipitation in NCEP’s NMM-WRF

21. Explosive Cyclogenesis Tropical Systems will tend to over intensify. –Look to NHC and GFS Extra Tropical Systems become overly compact.

22. Example of Intensified Tropical System

23. Explosive Cyclogenesis

24. dprog/dt Consistency and trends in an NWP model have long been used as a subjective forecasting technique by forecasters. This may provide little of no skill. Thomas M. Hamill. 2003: Evaluating Forecasters' Rules of Thumb: A Study of d(prog)/dt. Weather and Forecasting: Vol. 18, No. 5, pp. 933–937.

25. Conclusions The NCEP NMM-WRF implemented on Jun 13 th is a very different Model than eta. It is not a magic solution. Improvements? –Yes! –Higher Terrain –Mountain Wave –Details

26. Conclusions What to watch out for? –Excessive Rainfall –Higher vertical velocities in strong systems –Spurious Tropical Cyclones –Over intensified Cyclones.

27. References Operational Models Matrix: Characteristics of Operational NWP Models: http://www.meted.ucar.edu/nwp/pcu2/index.htm More Detailed Presentation at COMET: http://meted.ucar.edu/nwp/NAMWRF_short/ WRF Home Page http://wrf-model.org/index.php