Anomaly Forecast—Useful Tool for Extreme Weather Detection

In 2006, an NCEP Global Ensemble Forecast System (GEFS) and North American Ensemble Forecast System (NAEFS) have been implemented to improve probabilistic forecast through anomaly forecast of various weather elements. Anomaly forecast is one of NAEFS products after forecast bias correction from current analysis, and measuring the forecast departure from climatology. Based on NCEP/NCAR 40 years reanalysis, daily climatological distribution (PDF) has been build up for 19 atmospheric variables, such as height, temperature, winds and etc. The uncertainty information for anomaly by comparing forecast PDF to climatological PDF allows users to identify the extreme weather event easily. There are many applications in past years for extreme heat waves, winter storms and etc.

In this study, a new daily climatology, which is from latest CFS reanalysis (30 years), has been generated to compare with the NCEP/NCAR 40 years reanalysis. Apparently, CFSR has much improved quality through the observations, assimilation methodology and forecast model. The new climatology based anomaly forecast for NAEFS will be implemented to replace current climatology. Anomaly forecast for SREF is planning to be implemented in the future, ether. Meanwhile, the model climatology, based on GEFS reforecast (25 years), has been created to produce another set of anomaly forecast from raw ensemble forecast (no bias correction). The subjective evaluations of all these applications will be carried out to identify the values.