CAPS REALTIME 4-KM MULTI-MODEL CONVECTION-ALLOWING ENSEMBLE AND 1-KM CONVECTION-RESOLVING FORECASTS FOR THE NOAA HAZARDOUS WEATHER TESTBED 2009 SPRING EXPERIMENT

In the spring of 2009, the Center for the Analysis and Prediction of Storms (CAPS) continues its participation in the NOAA Hazardous Weather Testbed (HWT) Spring Experiment by providing storm-scale ensemble and high-resolution deterministic forecasts for evaluation by HWT. Improving upon the configurations of the previous two years, the 4-km ensemble is expanded to include three dynamic cores, that is, the WRF-ARW, WRF-NMM and the ARPS, and the ensemble size is doubled from 10 to 20. The ensemble members will include both initial condition/boundary condition perturbations and physics diversity. Furthermore, level-2 radial velocity and reflectivity data from over 120 operational WSR-88D radars will be analyzed using an improved version of the ARPS 3DVAR together with its cloud analysis package. The radar-containing analysis serves at the control initial condition onto which perturbations are added. Thirty-hour forecasts will be produced once per day, on a domain that covers nearly the entire continental US (CONUS). The high-resolution deterministic forecasts will have a 1 km horizontal resolution, covering the same near-CONUS domain and will also contain all radar data. Such efforts are truly unprecedented and require the largest supercomputers at NSF supercomputing centers. Code parallelization and optimization of the entire prediction workflow is required for the effort to be possible.

This paper will report on the experimental design and discuss logistic issues. It will present examples of ensemble and deterministic forecasts, and verifications against radar observations. Particular emphasis will be given to the value of radar data assimilation and the effect of resolution on short- and longer-range forecasts. A comparison paper will focus on the evaluation of the ensemble forecasts and products.