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CFS forecast Assessment for 2006

A detailed evaluation of the CFS forecast for 2006, focusing on Tropical SSTs and response in precipitation and z200. The report covers observed anomalies, forecast patterns, and correlation skills for different regions and variables. Despite capturing some warming trends, the forecasts generally lagged behind observations, especially in the second half of the year. Analysis highlights strengths and weaknesses in forecast accuracy and skill across various target months and ensemble members.

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CFS forecast Assessment for 2006

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  1. CFS forecast Assessment for 2006 • Tropical SSTs • Response in precipitation and 200mb height (z200) • Forecasts of North America z200, precipitation and T2m

  2. 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

  3. Tropical SSTs

  4. Monthly Nino34 SST anomalies (K) • Observations are encompassed in the forecast ensemble; but • Most forecast members for 2006 are too cold

  5. 2006 seasonal mean Nino34 SST anomalies (K) 2006 • The forecasts captured the warming trend; but lagged observations by a few months

  6. Spatial correlation and RMS error of 2006 seasonal mean tropical (30S-30N) 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.

  7. Response in precipitation and z200

  8. 0.4 0.3 -0.3 Pattern correlation of tropics (30S-30N) 1-month-lead forecast • Relatively low skill for one-month lead (~0.4 for SST and ~0.3 for precipitation) • Negative z200 correlation for all seasons, except for MAM

  9. 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 central-eastern tropical Pacificin AMJ, when observed are near normal.

  10. 2006 anomalies (K) Observed Precipitation z200 One-month-lead Forecast

  11. Forecasts of North America z200, precipitation and T2m

  12. Pattern correlation skill Precipitation 2006 Nino34 SST anomalies (K) T2m Z200 • Positive (negative) correlations in the first (second) half. • Highest skill in northern spring when observed Nino34 SST anomalies are near zero and forecast SST anomalies are incorrectly about -1K.

  13. Similar annual variation in correlation skill in T2m and z200 in 2005 and 2006.

  14. North America 2006 anomalies Observation T2m Precipitation Forecast Precipitation T2m

  15. Annual mean

  16. 2006 Annual mean SST T2m Obs • Forecast precipitation pattern in the tropical Pacific and Indian Oceans similar to the observed. • Too cold SSTs, below normal below-normal z200, and less warm temperature over most of the globe in the forecast. Fcst Precipitation z200 Obs Fcst

  17. Summary • Tropical SSTs in the tropical Pacific underwent a warming trend in 2006 • Observed Nino34 SSTA increased from -1K in Jan to 1K in Dec • CFS followed but lagged the observed trend; forecast anomalies too cold • Forecast pattern correlation skill in the tropics (30S-30N) is low • SST: ~0.4; precipitation: ~0.3; z200: -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 z200 anomalies • forecast T2m less warm over most of the globe in the forecast

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