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NOAA/NWS Change to WRF

NOAA/NWS Change to WRF. 13 June 2006. What’s Happening?. WRF replaces the eta as the NAM NAM is the N orth A merican M esoscale “timeslot” or “Model Run” at NOAA/NWS’s National Center for Environmental Prediction (NCEP). NMM is not a MODEL !

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NOAA/NWS Change to WRF

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  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 13th 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

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