The APCC seasonal forecast is based on multi-model ensemble (MME) prediction system and disseminated to APEC member economics around 20th of every month. Currently, 15 operational centers and research institutes from 11 countries around the world participate in the APCC MME operational prediction system by routinely providing their predictions in the form of ensembles of global forecast fields. The APCC's real-time operational forecasts are issued in both deterministic (based on ensemble mean) and probabilistic (based on full set of ensemble members) forms and more detailed description of the methods is as follows.
The deterministic forecast is based on a simply average of bias-corrected ensemble means from each model with equal weight to create a multi-model forecast. The ensemble mean anomaly forecasts for each individual model is calculated by their own climatology from the hindcasts.
The probabilistic forecast is based on an uncalibrated MME with model weights being proportional to the square root of ensemble size, and a Gaussian fitting method for the estimation of the tercile-based categorical probabilities, that is, the probability of below-normal (BN), near-normal (NN), and above-normal (AN) categories with respect to climatology (Min et al. 2009). The procedure for the probabilistic forecast consists of following two steps.
The upper and lower terciles are determined separately for each model using their mean and standard deviation of hindcasts. Then, the forecast probability for each category is estimated as a portion of the cumulative probability of their forecast sample associated with the category.
The forecast probabilities for each model are averaged together with model weights being inversely proportional to the random errors in the forecast probability associated with the standard error of the ensemble mean (i.e., proportional to the square root of ensemble size) to create a probabilistic multi-model ensemble forecast.
|NASA||United States of America||GEOS-S2S-2.1|
|NCEP||United States of America||CFSv2|
|Name||Abbreviation for file name||Unit|
|Sea level pressure||slp||hPa|
|Sea surface temperature||sst||K|
|Temperature at 2m||t2m||K|
|Temperature at 850hPa||t850||K|
|Zonal wind at 200hPa||u200||m s-1|
|Zonal wind at 850hPa||u850||m s-1|
|Meridional wind at 200hPa||v200||m s-1|
|Meridional wind at 850hPa||v850||m s-1|
|Geopotential height at 500hPa||z500||m|
Monthly and seasonal data up to 6 months lead time
*Lead time means the length of time between the issuance of a forecast and the occurrence of the phenomena that were predicted.
Global data whose resolution is 2.5°×2.5°