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Model Evaluation Tools(MET): An Overview
MET Verification Techniques
• Standard verification methods – gridded model data to point-based
observations – gridded model data to gridded observations
• Object-based verification method – comparing gridded model data to gridded
observations
Working Example:6-h precip forecast valid 00z 2 June 08
Forecast
Observations
Stage IV Hourly Precip Files
• ST4.2008060119.01h
• ST4.2008060120.01h
• ST4.2008060121.01h
• ST4.2008060122.01h
• ST4.2008060123.01h
• ST4.2008060200.01h
4-km Stage IV grid Specification
1121 x 881 polar stereographic grid. LL point: 23.117N 119.023W. UL point: 53.509N 134.039W. LR point: 19.805N 80.750W. UR point: 45.619N 59.959W.
True longitude: 105W. The resolution is 4.7625km at 60N.
The pole point is (I,J) = (400.5,1600.5)
This and numerous other standard grids defined at:http://www.nco.ncep.noaa.gov/pmb/docs/on388/tableb.html
PCP-Combine command options
pcp_combine init_time
in_accum
valid_time
out_accum
out_file
[-pcpdir path]
[-pcprx reg_exp]
PCP-combine command options
• init_time: – Initialization time of the input Grib files in
YYYYMMDD_HHMMSS format (required).• in_accum:
– Accumulation interval of the input Grib files in HH format (required).
• valid_time: – Desired valid time in YYYYMMDD_HHMMSS format (required).
• out_accum: – Desired accumulation interval for the output NetCDF file in HH
format (required).• out_file:
– Name of the output NetCDF file to be written consisting of the sum of the accumulation intervals (required).
PCP_combine example: Summing individual Stage IV hourly precip
• pcp_combine -sum 00000000_000000 01 20080602_000000 6 obs_6hr.nc -pcpdir .– Note: Set init_time to 00000000_000000
when summing observation files
• Above command yields 6-hour OBS precip valid at 00z 2 June 2008 in netcdf format– Filename “obs_6hr.nc”
Regrid forecasts with “copygb”
• STIV Obs Grid – 1121x881,polar stereo,Dx,Dy 4763
• WRF Data Grid– 308 x 310; Lambert Proj with Dx,Dy = 4000– Extract precip grid from WRF output GRIB file– Needs to be projected onto OBS grid (i.e. Stage IV)– wgrib –V filename: provides necessary details on
each grid
Regrid forecasts with “copygb”
Output of wgrib –V on Stage IV file yields:polar stereo: Lat1 23.117000 Long1 -119.023000 Orient -105.000000, north pole (1121 x 881) Dx 4763 Dy 4763 scan 64 mode 8
set grid="255 5 1121 881 23117 -119023 8 -105000 4763 4763 0 64"
WRF Forecast GRIB files: 03z 1 June initialization time
• copygb -xg "$grid" -i1 -X WRFPRS15.tm00.d01.grb WRFPRS15.tm00.d01.grb.new
• copygb -xg "$grid" -i1 -X WRFPRS21.tm00.d01.grb WRFPRS21.tm00.d01.grb.new
PCP-Combine for WRF files:Subtract 15-h from 21-h precip
• pcp_combine -subtract WRFPRS21.tm00.d01.grb.new 21 WRFPRS15.tm00.d01.grb.new 15 WRFPRS_6hr.nc
MODE command
mode fcst_file obs_file Config_file [options]
Configuration file: WrfModeConfig
mode WRFPRS_6hr.nc obs_6hr.nc WrfModeConfig
MODE output
• 3 output formats– ASCII,NetCDF,PS
• mode_APCP_06_SFC_vs_APCP_06_SFC_240000L_20080602_030000V_060000A_cts.txt
• mode_APCP_06_SFC_vs_APCP_06_SFC_240000L_20080602_030000V_060000A_obj.nc
• mode_APCP_06_SFC_vs_APCP_06_SFC_240000L_20080602_030000V_060000A_obj.txt
• mode_APCP_06_SFC_vs_APCP_06_SFC_240000L_20080602_030000V_060000A.ps
No Mask Masking Obs
0.1 mm thresh 5.0 mm thresh
Centroid radius variations800/(delta-x) 200/(delta-x)