The NCEP's Climatology-Calibrated Precipitation Analysis (CCPA) Version 4

Inspired by a need for a best analysis at high temporal and spatial resolutions for precipitation verification, calibration and downscaling, NCEP Environmental Modeling Center has developed Climatology-Calibrated Precipitation Analysis (CCPA). CCPA is a precipitation analysis at about 5km resolution with 6 hour accumulation over the Contiguous United States (CONUS). Utilizing linear regression and spatial and temporal downscaling techniques, this 6-hourly analysis product is generated by combining two widely used datasets by taking advantage of the higher reliability of the NCEP CPC Unified Global Daily Gauge Analysis and the higher temporal and spatial resolution of the NCEP EMC Stage IV multi-sensor quantitative precipitation estimations (QPEs). CCPA was first implemented into operations in July 2010 and experienced twice upgrades afterwards. The product is available to users at six basic grids with 3 hour and 6 hour accumulations from 2002 to present. At EMC CCPA provides a proxy of truth for the bias correction and statistical downscaling of precipitation forecasts from the NCEP GFS Ensemble Forecast System (GEFS) and Short Range Ensemble Forecast System (SREF) products, and precipitation verifications in evaluating the performance of various forecast systems. In recent years, CCPA application is also expanded to the National Blender Models (NBM) projects led by MDL, who applies CCPA as the ground truth to mitigate high bias on 12-h probabilitic forecasts of precipitation.

To continuously support the NBM projects, an upgrade to the version 4 of CCPA (CCPAv4) is undergoing and scheduled for operational implementation at NCEP in early 2018. With the new version CCPA will be improved and expanded. The upgrade includes: 1) updating the regression coefficients with extended historical training data sets from 2002 to 2017, which is the most important enhancement to CCPA; 2) inclusion of hourly analysis at request of MDL and other users; 3) change to 3-hourly CCPA due to an upcoming improved data quality of Stage IV hourly data both in NWRFC and CNRFC areas. To ensure a better representation of precipitation over the western part of the U.S, Stage IV hourly will be only used instead of currently a blended Stage IV-Stage II hourly as weights to produce 3-hourly CCPA. In this presentation, all enhancements will be described, evaluated and validated. Especially the evaluation will be carried out by a comparison of the original and new products against rain gauge observations. Finally a summary of the presentation and results will be given.