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.

Evolution of Numerical Models

NCEP Operational Regional Model Penn State/NCAR Mesoscale

Model

Year Model Resolution Year Model

1955 Princeton QG 381 km /3 levels 1969 3-D Hurricane / 30 km

1966 Primitive Equation 381 km /6 levels 1971 Began MM0 – MM3 devel

1971 Limited Area Fine

Mesh (LFM)

190.5 km / 7

levels

1981 Began MM4 development

1985 Triply Nested Grid

(NGM)

80 km / 16

levels

1987 MM4 released to community

1993 ETA 80 km / 38

levels

1990 First R-T MM4 fcst (30 km)

1995 Meso-Eta 29 km / 50

levels

1994 MM5 (non-hydro) released

1996 Nested Eta

(experimental)

10 km / 60

levels

1997 MM5 adjoint system

1998 ETA 32 km / 45

levels

1998 ATEC 1.1 km real-time

2000 ETA 22 km / 50

levels

2001 ETA 12 km / 60

levels

2001 Danny simulation – 1 km

2002 Non-hydrostatic

(experimental)

8 km / 60 levels 2002 Columbia Gorge simulation

at 440 m (U. of Washington)

3-D Trajectories

Anthes’ hurricane simulation30 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

• Strongest winds are at the exit

Portland

Troutdale

Cascade Locks

36h WRF Precip Forecast

Analyzed Precip

27 Sept. 2002

Goals: Develop an advanced mesoscale forecast and assimilation system, and accelerate research advances into operations

• Collaborative partnership, principally among NCAR, 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

Weather Research and Forecasting Model

• 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.

WRF Model Characteristics

• 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 Software Design

Mediation Layer

Driver Layer

Model Layer

WRF Parallel Scaling

0

50

100

150

0 500 1000processors

Gfl

op

/s

IBM Regatta

IBM Winterhawk IIIntel

COMPAC

27km WRF Model

Ocean SST Wave Height

Mobile Bay

WRF Performance Benchmarks

• WRF Version 1.3

• 12-km CONUS

• 500 times real time

equivalent to 48 h

forecast in 6 mins.

• No I/O or

initialization

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?

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

10 km WRF forecast domain4 km WRF forecast domain

Field program conducted 20 May – 6 July 2003

Real-time WRF 4 km BAMEX Forecast

Composite NEXRAD RadarReflectivity forecast

Initialized 00 UTC 9 June 03

Real-time WRF 4 km BAMEX Forecast

Composite NEXRAD Radar

4 km BAMEX forecast 36 h Reflectivity

4 km BAMEX forecast 12 h Reflectivity

Valid 6/10/03 12Z

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

Composite NEXRAD Radar

4 km BAMEX forecast

Valid 6/10/03 12Z

10 km BAMEX forecast

22 km CONUS forecast

Realtime WRF 4 km BAMEX Forecast

Composite NEXRAD Radar30 h Reflectivity Forecast

Squall line

7” hail 00Z

Valid 6/23/03 06Z

Real-time WRF 4 km BAMEX Forecast

Initialized 00 UTC 12 June 03

Reflectivity forecast Composite NEXRAD Radar

Realtime WRF 4 km BAMEX Forecast

Composite NEXRAD Radar30 h Reflectivity Forecast

Missed

Valid 6/12/03 06Z

Criteria:

Within 400 km and 3 h Probability of

Detection

False Alarm

Corresponding

mesoscale

convective systems

58% 29%

For squall line or

quasi-linear

convection

79% 29%

Most organized

mode for each

forecast period

80% 7%

Skill of Storm-scale prediction

From Done, Davis and Weisman (2003)

10-km WRF4-km WRF

Dashed magenta indicates approximate area of rainfall

Produced by convective parameterization

Parameterized convection (on the 10 km grid) cannot differentiate different mode of convection

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

•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

Challenge:

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, andGFDL 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

• 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

http://www.mmm.ucar.edu/wrf/WG2/software_2.0

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

Thank you!