## Introduction

The NCEP Climate Forecast System (CFS) was developed in 2003 and
implemented in August 2004 for seasonal climate forecast. This pege provides diagnoses of
CFS overall performance based on its retrospective forecasts (or hindcasts) for initial
months from January 1981 to December 2006. Forecasts for each initial month consist of
fifteen members with five members from the end of the initial month, and five members from
the 21st and five members from the 11th of the initial month. Each forecast has been made for
9 target months. Verification is cross validated by taking forecast anomalies as deviations
from time average of 25 years that do not include the year of target months.

The plots include statistics for two-dimentional (xy and xz) fields,
indices of sea surface temperature (SST) and emperical modes of atmospheric circulation.
The SST indices include: Nino1+2(80W-90W,10S-EQ), Nino3(150W-90W,5S-5N), Nino34(170W-120W,5S-5N),
Nino4(160E-150W,5S-5N), Hurricance MDR (20W-80,10N-20N). The indices of atmospheric circulation
modes include: 500-hPa PNA, 500-hPa NAO, and 1000-hPa AO, which are calculated based on monthly mean anomaly fields. A single
pattern is calculated for each mode. Seasonality is not considered in the EOF calculation.
For both monthly and seasonal mean, indecies are obtained by projecting
anomaly fields onto observed modes calculated based on monthly mean.

Statistics are calculated for both monthly mean for 0-8 month lead, and seasonal mean for 0-6
month lead. Climatology and bias of the forecast are calculated as 26 year average (1981-2006).
Anomalies for calculating statistics are corss-validated by taking anomalies as deviations
from time average of 25 years that do not include the year of target months.

Observations used in the calculations
SST |
OIv2 |

SSH, TEQ |
GODAS |

Precipitation |
CMAP |

T2m |
CPC ghcn_cams |

z200, z700, z1000, u200, u850 |
NCEP R2 |