Recent Upgrades to the NCEP Stage IV Precipitation Analysis

The NCEP “Stage IV” is the 4km hourly/6-hourly/24-hourly precipitation analysis mosaicked from the primarily radar and/or gauge-based hourly/6-hourly regional QPEs produced at the 12 ConUS River Forecast Centers. Initially developed to serve as input for precipitation assimilation in NCEP's mesoscale modeling system, over time it became widely used in forecast operations and research communities both inside and outside of NWP. At NCEP, in addition to its original role, it is also used for QPF verification, as precipitation driver for land surface modeling, and is the basis for the Climatology-Calibrated Precipitation Analysis (CCPA, through which it is used for bias corrections and down-scaling of regional and global ensemble precipitation forecasts), and the precipitation component in the UnRestricted Mesoscale Analysis (URMA).

Originally the focus of the Stage IV mosaic was in the hours immediately following the validation time (for real time data assimilation), as regional QPEs are initially filled in/re-made at the RFCs, and the Stage IV mosaic was updated hourly for 1-2 days after validation time. To better serve the diverse needs of a wide user base, in Apr 2015 we expanded the look-back period to 7 days: additional re-mosaics are made at 1/3/5/7-days after validation time, in case one or more RFC should make a late update as new data/QC information becomes available. In addition, for the 6-hourly Stage IV, instead of a simple mosaic of 6-hourly input from the RFCs, hourly QPEs from the Eastern/Central RFCs are summed into 6-hourly totals, then combined with 6-hourly QPEs from the four Western RFCs, to take into account regional differences in base (primary) analysis.

Another upgrade of the Stage IV/RTMA/URMA system is planned for late 2015, at which time we plan to 1) use hourly Stage IV as primary source for the Real Time Mesoscale Analysis (RTMA), supplemented by the hourly Stage II (currently the Stage II is the sole source of the RTMA); 2) refine the Stage IV mosaic process on where an RFC's data might be used outside of its domain of primary responsibility. Details of changes and the impact of the two upgrades will be discussed at the presentation.