noaa/nws change to wrf 13 june 2006. what’s happening? wrf replaces the eta as the nam –nam is...
TRANSCRIPT
NOAA/NWS Change to WRF
13 June 2006
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.
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
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.
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.
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).
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.
New Snow Cover Analysis
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
The Vertical Coordinate Systems
Terrain
• Because of the sigma coordinate system, terrain is more realistic in WRF
Terrain in the Northeast
http://www.meted.ucar.edu/nwp/pcu2/wrftopo/topocompare.htm
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.
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.
What’s Not Changed
• Horizontal Resolution – 12 km
• Domain is the same
• Physics – Convective Parameterization– Planetary Boundary Layer
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.
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.
Problems?
• Heavier Precipitation
• Explosive Cyclogenesis
Heavier Precipitation
• While WRF has same convective scheme as eta, but non-hydrostatic effect can result in significant additional amounts in the QPF Field.
Extra Convective Precipitation in NCEP’s NMM-WRF
Explosive Cyclogenesis
• Tropical Systems will tend to over intensify.– Look to NHC and GFS
• Extra Tropical Systems become overly compact.
Example of Intensified Tropical System
Explosive Cyclogenesis
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.
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
Conclusions
• What to watch out for?– Excessive Rainfall– Higher vertical velocities in strong systems– Spurious Tropical Cyclones– Over intensified Cyclones.
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 Pagehttp://wrf-model.org/index.php