16B.4 NAEFS based bias correction and statistical down scaling

Thursday, 4 June 2009: 4:45 PM
Grand Ballroom West (DoubleTree Hotel & EMC - Downtown, Omaha)
Bo Cui, NOAA/NWS/NCEP/EMC, Camp Springs, MD; and Y. Zhu, D. Hou, and Z. Toth

The North American Ensemble Forecast System (NAEFS) was established in 2004 by the Meteorological Service of Canada (MSC), the National Meteorological Service of Mexico (NMSM), and the US National Weather Service (NWS) as an operational multi-center ensemble forecast system. Currently it combines the 20-member MSC and NWS ensembles to form a joint ensemble of 40 members twice a day after bias correction, down scaling for selected variables. The probabilistic forecast products have been delivered to users since 2006.

Basic NAEFS products are bias corrected global ensemble forecasts at 1 by 1 degree (about 110km) resolution. Probabilistic forecasts (10%, 50%, 90%), ensemble mean, spread and mode are generated for 35 selected variables, twice per day, out to 16 days. Anomaly forecasts are produced for 19 selected variables, too.

A statistical downscaling method was implemented at NCEP for NAEFS since December 2007. This approach is an attempt to establish the relationship between coarse and fine resolution data and project coarse resolution information onto finer grid. The operational Real-Time Mesoscale Analysis (RTMA) for CONUS with 5-km resolution (NDGD grids) is chosen as the true when compared with analysis which interpolated from NCEP Global Data Assimilation System (GDAS) to 5-km resolution. The difference between the two analyses are accumulated by adopting a decay averaging algorithm and used as a Downscaling Vector in the downscaling process. The results show that this downscaling method can effectively reduce systematic forecast errors. The downscaled forecast also displays more detailed forecast information than the raw forecast.

Currently, downscaled 5km NAEFS products for CONUS have been in NCEP operation for 4 variables (T2m, surface temperature, U10m and V10m). Downscaling products for Alaska, Hawaii, and other regions will be in operation soon.

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