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Fedor Mesinger

Since 9 June 1993, the eta coordinate regional model has been run twice daily at the National Centers for Environmental Prediction (NCEP, previously the National Meteorological Center) as the NCEP's “early” operational model. Its performance is regularly monitored in a variety of ways, with particular attention given to precipitation forecasts. Throughout this period, the eta model has demonstrated significantly increased accuracy in forecasting daily precipitation amounts compared to NCEP's Nested Grid Model (NGM). The model has shown a smaller but equally consistent advantage in skill against that of NCEP's global spectral model.

Precipitation scores of these three operational models for the 6-month period March–August 1995 are presented. This interval is chosen because the 6-month-long periods September–February and March–August have been used in previous model comparisons and because an upgraded version of the eta model, run at 48-km resolution, was also regularly executed twice daily during the March–August 1995 period. It is thus included and highlighted in the present comparison. The 48-km eta carries cloud water as a prognostic variable and is coupled to a 12-h eta-based intermittent data assimilation system. It replaced the 80-km eta as the NCEP's early operational model on 12 October 1995.

Compared to the then-operational 80-km eta, the 48-km eta has demonstrated substantially increased skill at all eight precipitation categories for which verifications are made. The increase in skill was greatest for the most intense precipitation, at the threshold of 2 in. (24 h)−1. A 24-48-h forecast of accumulated precipitation, resulting from Hurricane Allison as it was crossing the extreme southeastern United States, is shown as an example of a successful forecast of intense precipitation by the 48-km model.

Reasons for the advantage of the eta model over its predecessor, the NGM, are reviewed. The work in progress is outlined.

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Fedor Mesinger, Geoff DiMego, Eugenia Kalnay, Kenneth Mitchell, Perry C. Shafran, Wesley Ebisuzaki, Dušan Jović, Jack Woollen, Eric Rogers, Ernesto H. Berbery, Michael B. Ek, Yun Fan, Robert Grumbine, Wayne Higgins, Hong Li, Ying Lin, Geoff Manikin, David Parrish, and Wei Shi

In 1997, during the late stages of production of NCEP–NCAR Global Reanalysis (GR), exploration of a regional reanalysis project was suggested by the GR project's Advisory Committee, “particularly if the RDAS [Regional Data Assimilation System] is significantly better than the global reanalysis at capturing the regional hydrological cycle, the diurnal cycle and other important features of weather and climate variability.” Following a 6-yr development and production effort, NCEP's North American Regional Reanalysis (NARR) project was completed in 2004, and data are now available to the scientific community. Along with the use of the NCEP Eta model and its Data Assimilation System (at 32-km–45-layer resolution with 3-hourly output), the hallmarks of the NARR are the incorporation of hourly assimilation of precipitation, which leverages a comprehensive precipitation analysis effort, the use of a recent version of the Noah land surface model, and the use of numerous other datasets that are additional or improved compared to the GR. Following the practice applied to NCEP's GR, the 25-yr NARR retrospective production period (1979–2003) is augmented by the construction and daily execution of a system for near-real-time continuation of the NARR, known as the Regional Climate Data Assimilation System (R-CDAS). Highlights of the NARR results are presented: precipitation over the continental United States (CONUS), which is seen to be very near the ingested analyzed precipitation; fits of tropospheric temperatures and winds to rawinsonde observations; and fits of 2-m temperatures and 10-m winds to surface station observations. The aforementioned fits are compared to those of the NCEP–Department of Energy (DOE) Global Reanalysis (GR2). Not only have the expectations cited above been fully met, but very substantial improvements in the accuracy of temperatures and winds compared to that of GR2 are achieved throughout the troposphere. Finally, the numerous datasets produced are outlined and information is provided on the data archiving and present data availability.

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