CFS forecast Assessment for 2006 Tropical SSTs Response

CFS forecast Assessment for 2006 • Tropical SSTs • Response in precipitation and 200 mb height (z 200) • Forecasts of North America z 200, precipitation and T 2 m

CFS forecast • Two forecast members per day • 9 target months • 40 -member ensemble from last 20 days of the month before the first target month • Climatology taken as 1982 -2003 average

Tropical SSTs

Monthly Nino 34 SST anomalies (K) • Observations are encompassed in the forecast ensemble; but • Most forecast members for 2006 are too cold

2006 seasonal mean Nino 34 SST anomalies (K) 2006 • The forecasts captured the warming trend; but lagged observations by a few months

Spatial correlation and RMS error of 2006 seasonal mean tropical (30 S-30 N) SST anomalies (K) • Correlations of 3 - and 6 -month lead forecasts are near zero for the second half of 2006. • Only one-month-lead forecasts will be presented next.

Response in precipitation and z 200

Pattern correlation of tropics (30 S-30 N) 1 -month-lead forecast 0. 4 0. 3 -0. 3 • Relatively low skill for one-month lead (~0. 4 for SST and ~0. 3 for precipitation) • Negative z 200 correlation for all seasons, except for MAM

2006 SST anomalies (K) Observed One-month-lead Forecast • More reasonable patterns in the Pacific; more erroneous in the Indian and Atlantic Oceans. • Forecast cold anomalies in the centraleastern tropical Pacific in AMJ, when observed are near normal.

2006 anomalies (K) Precipitation Observed One-month-lead Forecast z 200

Forecasts of North America z 200, precipitation and T 2 m

Pattern correlation skill Precipitation 2006 Nino 34 SST anomalies (K) T 2 m Z 200 • Positive (negative) correlations in the first (second) half. • Highest skill in northern spring when observed Nino 34 SST anomalies are near zero and forecast SST anomalies are incorrectly about -1 K.

• Similar annual variation in correlation skill in T 2 m and z 200 in 2005 and 2006.

North America 2006 anomalies T 2 m Observation Forecast Precipitation

Annual mean

2006 Annual mean SST T 2 m Obs • Forecast precipitation pattern in the tropical Pacific and Indian Oceans similar to the observed. • Too cold SSTs, below normal below-normal z 200, and less warm temperature over most of the globe in the forecast. Fcst Precipitation Obs Fcst z 200

Summary • Tropical SSTs in the tropical Pacific underwent a warming trend in 2006 Observed Nino 34 SSTA increased from -1 K in Jan to 1 K in Dec CFS followed but lagged the observed trend; forecast anomalies too cold • Forecast pattern correlation skill in the tropics (30 S-30 N) is low SST: ~0. 4; precipitation: ~0. 3; z 200: -0. 3 • North America, positive forecast skill in the first half of the year negative forecast skill in the second half of the year highest skill in northern spring season when tropical eastern Pacific SSTs are near normal in the observation and negative in the forecast • Annual mean, forecast SSTs too cold, CFS failed to capture observed positive z 200 anomalies forecast T 2 m less warm over most of the globe in the forecast