Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) Forum

Update on RUC upgrade - radar, TAMDAR, etc.

Posted By: Stan Benjamin
Date: 12-August-08 2318Z

Sorry for the recent radio silence, but... The RUC upgrade including assimilation of radar reflectivity, TAMDAR aircraft, and improvements to the model physics, is still on its way, planned for fall 2008, perhaps as early as next month (September). Here is an update that will appear in a NWS Technical Information Notification in the near future. In fall 2008, several changes will be made to the Rapid Update Cycle /RUC/ modeling-assimilation system. These changes are made to improve model performance. The model changes include: 1. Use of RRTM longwave radiation scheme, replacing previous Dudhia longwave radiation scheme 2. Modifications to Grell-Devenyi convective parameterization to reduce excessive areal coverage for light precipitation. 3. Modifications to RUC land-surface model – snow density change to prevent excessive cold 2-m temperatures over fresh snow, and snow melting limitation to improve 2-m temperatures for warm-air advection over snow cover. 4. Specification of latent heating from 3-d radar reflectivity during pre-forecast diabatic digital filter initialization (DFI) already in the RUC model. The analysis changes include: 1. Assimilation of 3-d radar reflectivity, combined with satellite and METAR cloud data to modify water vapor field, and for production of radar-based 3-d latent-heat specification to be included in RUC model DFI. 2. Assimilation of TAMDAR aircraft observations including moisture observations. 3. Assimilation of mesonet wind data using stations from a mesonet station wind uselist. 4. Revision to observation error and background error for moisture observations. 5. Improved QC based on mean observation-background differences for a given platform within a RUC analysis window. 6. Fix to assimilation of buoy observations. Other output changes include: 1. Add 4 additional 2-d fields to the RUC isobaric (pgrb) files: a. three reflectivity fields (maximum, 1-km, 4-km) similar to products already produced for the NAM, b. relative humidity relative to precipitable water for saturated column. 2. Add 4 additional 2-d fields to the RUC native (bgrb) files: a. Soil type, vegetation type, land-water mask, ice cover (similar to fields already produced for the NAM and GFS). b. Allows easier post-processing of RUC data or initialization of experimental models (e.g., WRF) using RUC initial conditions. 3. PDS time period descriptors for RUC precipitation for 1-h and 2-h periods are corrected. 4. No other output changes. THE COMBINED IMPACT OF THESE CHANGES HAS LED TO THE FOLLOWING IMPROVEMENTS IN MODEL PERFORMANCE: Reduces bias in 2-m temperature and 10-m wind speed for all times of day and all seasons. Improved precipitation and cloud forecasts for 1-h to 12-h durations. Improved ceiling and visibility forecasts Improved lower- to mid-tropospheric temperature and RH forecasts in Midwest and eastern US. Improved accuracy in temperature and wind fields for CONUS RTMA (which uses downscaled 1-h RUC forecasts as RTMA background). The combined impact of the RUC changes included in this project will incrementally improve the overall forecast skill of the RUC forecast. In addition to the assimilation of new observation types (radar reflectivity, TAMDAR, mesonet winds), the changes are intended to address known RUC weaknesses and biases as observed by NOAA/ESRL/GSD staff, EMC/MMB staff, NCEP Service Centers and NWS forecasters. More details about these changes are available at: http://ruc.noaa.gov/ruc13_docs/NCEP-CCB-RUCupgrade-12may08.pdf

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