THE CENTRAL WEATHER BUREAU REGIONAL CLIMATE DYNAMICAL DOWNSCALING FORECAST PRODUCTS FOR JFM 2011 HUI-LING WU and CHIH-HUI SHIAO

Introduction  CWB Regional Climate Dynamical Downscaling Forecast - The National Centers for Environmental Prediction regional spectral model (NCEP/RSM) - The Central Weather Bureau regional spectral model (CWB/RSM)  horizontal resolution - 60 km  Domain  East Asia (lat °E 、 long °N)  NCEP/RSM and CWB/RSM are nested in each AGCM forecast and hence form an ensemble of 30 downscaled forecasts, which are analyzed every month at CWB

Introduction  CWB Forecast products -The ensemble forecast anomaly of 850-hPa wind, precipitation and 2-meter temperature -The probability forecast with a three equiprobable categories method of precipitation and 2- meter temperature for the 4 subregions of Taiwan  The forecast is initialized at the beginning of Dec predicting Jan. to Mar  Global precipitation and 2-meter temperature analysis as well as 24 CWB surface stations observations were applied for the forecast verification.

Ensemble forecast of seasonal anomalous circulation over East Asia [850hPa Wind] Taiwan is influence of northeast anomaly. [Precipitation] Positive (wet) / Negative (dry) anomaly. [2-meter Temp.] Positive (warm) / Negative (cold) anomaly. The JFM 2011 ensemble forecast anomalies for 850-hPa wind, precipitation, and 2-meter temperature. C A

Ensemble forecast of monthly anomalies circulations over East Asia A A A C C C A Taiwan Island is under the influence of northeasterly anomaly. C

Ensemble forecast of monthly anomalous precipitation over East Asia [January] dry anomalies cover eastern China, the East China Sea, and the northern Philippines [February] Max. dry anomaly (estuary of Yangtze River) [March] The dry anomaly continues but intensifies and extends farther southwestward. Taiwan Island is under the influence of dry anomaly.

Ensemble forecast of monthly anomalous temperature over East Asia Taiwan Island is under the influence of cold anomaly. [January] cold anomalies area oriented northeast to southwest [February] cold anomaly enhanced and expansion to southwest coastal China and the ocean region west of Philippines. [March] The cold anomaly is strengthened and northern China is covered by the cold anomaly

Seasonal Probability forecast using a three equiprobable categories method Precipitati on 2-meter Temp. JFM 2011 probability forecasts of (a) precipitation and (b) 2-meter temperature over 4 subregions of Taiwan by the dynamical downscaling forecast system. The percentages in the tables are the probabilities of the forecast variables that fall into below, near, and above normal categories (from left to right). Statistically significant categories with probability greater than 33% are colored red.

Monthly Probability forecast using a three equiprobable categories method Precipitati on

Monthly Probability forecast using a three equiprobable categories method 2-meter Temp.

Forecast Validation for SON Circulation over East Asia for Precipitation Foreca st Observati on The ensemble forecasted precipitation and 2-meter temperature anomalies for SON 2010 are validated by the global observed anomaly of the same period Correctly predicted over the tropical and subtropical oceanic areas. An over-predicted dry (negative) anomaly area was found over central China

Forecast Validation for SON Circulation over East Asia for Temperature The forecast was quite skillful with the cold anomaly over southwestern China, but it over-predicted the warm anomaly over the entire southern portion of the model oceanic region. Foreca st Observati on

Probabilities forecasts and CWB observation of precipitation over 4 subregions of Taiwan Validating the predicted monthly forecasts against observation

Probabilities forecasts and CWB observation of 2-meter temperature over 4 subregions of Taiwan Overall, the confidence for precipitation forecasts was marginal and the 2-meter temperature forecasts appeared to be skillful for the target season.

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