NCEP Global Ensemble Based Anomaly Forecast

Recently, an NCEP Global Ensemble Forecast System (GEFS) has been implemented to improve probabilistic forecast. More importantly, North American Ensemble Forecast System (NAEFS) has operationally generated products since May 30 12UTC 2006. Anomaly forecast in percentile is one of NAEFS products after bias correction from current analysis. 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.. This anomaly uncertainty information allows users to create climatological percentiles to correspond to any percentile forecast values, such as 10 (or 5, low extreme), 50 (medium), and 90 (or 95, high extreme) percentile bias corrected forecast values. For example, a low extreme (5%) of ensemble 2 meter temperature forecast could be much above climatological normal (or high percentile) which indicates high probability of high temperature extreme. It could be heat wave in Northern Hemisphere summer season if it combines high humidity. If it is downscaled from current one by one degree forecast to 5 kilometer resolution by applying local climatology and high resolution analysis (such as RTMA, Real-Time Mesoscale Analyses), this product could be future part of NDGD (National Digit Guidance Database) uncertainty information to users.