NCEP EDAS and GDAS (FNL) Model Data

NCEP EDAS and GDAS Model Data is digital data set DSI-6141, archived at the National Climatic Data Center (NCDC). The National Centers for Environmental Prediction (NCEP), part of the US National Weather Service (NWS), runs a series of computer analyses and forecasts operationally that use or produce model data. DSI-6141 is one of these sets of NCEP model data that is archived at NCDC. DSI-6141 is actually a pair of closely related data sets, sometimes referred to at NCDC as EDAS (DSI-6141A), and GDAS or Final (FNL) (DSI-6141B). Eta Data Assimilation System (EDAS) has been run since 1995 and covers only the geographical US. It is an intermittent assimilation system consisting of successive 3 hourly Eta model forecasts and Optimum Interpolation analyses on a 40 km grid. The Air Resources Laboratory (ARL) extracts every second grid point to produce a 3 hourly 80 km grid, which is archived at NCDC. Major parameters in EDAS are (1) Surface parameters: Surface and sea level pressure; temperature at surface and at 2m above ground level (AGL); 3-hourly total and convective accumulated precipitation; soil moisture content; relative humidity at 2m AGL; u- and v-components of wind at 10m AGL; snow (yes/no); rain (yes/no); latent and sensible heat net flux at surface; low, medium, and high cloud cover; and downward short wave radiation flux. (2) Upper air parameters: U- and v-components of wind with respect to grid; geopotential height; temperature; pressure vertical velocity; and relative humidity. The Global Data Assimilation System (GDAS) part of this data set has archived data at NCDC back to 1997 and is a global data set. GDAS is the final run in the series of NCEP operational runs; it is therefore sometimes known as the Final Run (FNL). It is run 4 times a day for 00, 06, 12, and 18 UTC. Model output is for the anlysis time and a 6-hourly forecast. NCEP post-processing of GDAS converts the data from spectral coefficient form to 1 degree latitude-longitude (360 by 181) grids and from sigma levels to mandatory pressure levels. ARL converts the data to 129 by 129 polar stereographic grids for each hemisphere. The ARL version is the data archived at NCDC. Major parameters in GDAS (FNL) are: (1) Surface parameters: Surface and sea level pressure; temperature at surface and at 2m above ground level (AGL); 6-hourly total precipitation; u- and v-components of momentum flux at surface; latent and sensible heat flux at surface; downward short wave radiation flux at surface; relative humidity at 2m AGL; u- and v-components of wind at 10m AGL; soil moisture content; and total cloud cover. (2) Upper air parameters: U- and v-components of wind with respect to grid; geopotential height; temperature; pressure vertical velocity; and relative humidity. GDAS begins in 1997. NCEP global model data for the period 1991-1996 is archived at NCDC as digital data set DSI-6140, NCEP Nested Grid Model (NGM) and Medium Range Forecast (MRF) Archive.