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)