The Weather Research and Forecasting WRF Modeling System

1
The Weather Research and Forecasting (WRF)
Modeling System

• NASAs Short-term Prediction Research and
  Transition (SPoRT) Center
• 12 October 2005

2
Overview of WRF

• A next-generation mesoscale model and
  assimilation system, with an emphasis on
  horizontal resolutions of 1 10 km
• A number of different dynamics and physics
  options are available, so many different
  configurations of WRF are possible

3
Significance of WRF to the NWS

• Intended to promote closer ties between research
  and operations
• Will replace the PSU/NCAR MM5 and the Eta and RUC
  models at NCEP

4
SPoRT WRF configuration

• 00 and 12 UTC cycles
• 48 hour forecasts, output every 3h
• 36 km domain and 12 km nest with 37 vertical
  levels
• Initialized with 40 km NCEP EDAS analyses
• NAM 3h forecasts are used for LBCs

5
SST Initial Conditions in SPoRT WRF

• The SST initial conditions, originally from the
  RTG SST product, are replaced by a MODIS SST
  composite for both the 36 km and 12 km domains
• The MODIS SST composite provides more horizontal
  structure

MODIS SST - RTG SST 12 UTC August 16, 2005
Differences 2K
6
SPoRT WRF dynamics and physics

• Eulerian mass core
• Lin et al. microphysics
• RRTM LW radiation
• Dudhia SW radiation
• Noah land surface model
• YSU PBL scheme
• Kain-Fritsch cumulus parameterization scheme

3h forecast 3h accumulated precipitation
WRF
NAM
7
Availability in AWIPS

• Typically available by 1215 am/pm CDT
• time improvements are possible for the future
• Forecasts are available on the 12 km domain
• Access the WRF in AWIPS just like the NAM or GFS

8
WRF Assessments

• Assessments are conducted to study something of
  interest to both researchers and forecasters
• Surveys for WRF Assessment
• Separate for long-term and short-term desk
• Focused on temperature, precipitation, and clouds
• Measured confidence in WRF, Eta, and GFS

9
Summarized WRF Assessment Results
Forecasters had high confidence in all WRF
precipitation categories and moderately-high
confidence in cloud timing and location
There was less confidence in the WRF 2m
temperature
Long-term desk
Short-term desk
10
29 August 2004 Precipitation

• No model forecasted the correct amount of
  precipitation
• All models had some precipitation over the
  Huntsville area

11
29 August 2004 Cloud cover

• The Eta and GFS have a much thicker cloud field
  than the WRF

12
29 August 2004 2m Temperature

• The WRF model, with its thin cloud cover, has
  temperatures much higher than the Eta or GFS
• Thick cloud cover was observed at this time,
  associated with the convection observed in the
  precipitation fields
• For 2m temperature, the Eta and GFS outperformed
  the WRF for this case

13
00 UTC 4 August 2005
24h forecast 3h accumulated precipitation
NAM
WRF
Composite radar reflectivity
14
12 UTC 25 August 2005
Composite radar reflectivity
15
Summary

• Expect the WRF to have utility in forecasting
• Designed for mesoscale modeling
• High-resolution SSTs should improve forecasts,
  particularly near the coast
• Initial studies indicate it provides value beyond
  current operational models