NCAR’s Experimental Real-Time Convection-Allowing Ensemble Prediction System

Abstract

This expository paper documents an experimental, real-time, 10-member, 3-km, convection-allowing ensemble prediction system (EPS) developed at the National Center for Atmospheric Research (NCAR) in spring 2015. The EPS is particularly unique in that continuously cycling, limited-area, mesoscale ensemble Kalman filter analyses provide diverse initial conditions. In addition to describing the EPS configurations, initial forecast assessments are presented that suggest the EPS can provide valuable severe weather guidance and skillful predictions of precipitation. The EPS output is available to operational forecasters, many of whom have incorporated the products into their toolboxes. Given such rapid embrace of an experimental system by the operational community, acceleration of convection-allowing EPS development is encouraged.

The Community Leveraged Unified Ensemble (CLUE) in the 2016 NOAA/Hazardous Weather Testbed Spring Forecasting Experiment

“…The NCAR members also had a slightly different domain and used a one year 171 older version of WRF, which was necessary because their members were from an already 172 established ensemble system whose configuration was based on extensive testing and 173 verification (Schwartz et al 2015a). The NCAR group did not want to risk introducing changes 174 unwanted systematic biases.…”

Assessing the Skill of Convection-Allowing Ensemble Forecasts of Precipitation by Optimization of Spatial-Temporal Neighborhoods

“…In Germany, scholars used the Consortium for Small Scale Modeling (COSMO) model to conduct some convection-allowing ensemble forecast experiments [2,3]. In America, the National Center for Atmospheric Research (NCAR) and the Center for Analysis and Prediction of Storms (CAPS) conducted a series of convection-allowing ensemble forecast experiments [4][5][6][7][8][9][10] focusing on the evaluation of precipitation and extreme weather indications, which aroused interest in the study of convection-allowing ensemble forecasts. NCAR carried out continuous convection-allowing ensemble forecast experiments and case studies over the Conterminous United States (CONUS) with an inner 3-km resolution, and had a preliminary analysis on the forecast results [4,5].…”

On the forecast skill of a convection-permitting ensemble

“…To name but a few, there are the COSMO-DE-EPS (Consortium for Small-scale Modeling -EPS, Gebhardt et al, 2011;Peralta et al, 2012;Ben Bouallègue et al, 2013;Kühnlein et al, 2014) at the Deutscher Wetterdienst (DWD), the CP version of UK Met Office's MOGREPS (Met Office Global and Regional Ensemble Prediction System, Bowler et al, 2008;Caron, 2013;Hanley et al, 2013;Tennant, 2015), a storm-scale ensemble forecast (SSEF) run by the Center of Analysis and Prediction of Storms (CAPS) at the University of Oklahoma (Xue et al, 2007Clark et al, 2011;Schumacher et al, 2013;Schumacher and Clark, 2014), WRF-based CP ensemble at NCAR (e.g., Schwartz et al, 2015), and AROME-EPS (e.g., Bouttier et al, 2012) developed at Météo France. A common feature of all of these EPSs is that their horizontal mesh size is equal to or less than 4 km, but mostly between 2 and 3 km.…”

“…Some of them apply an ensemble data assimilation (EDA) approach for perturbing the initial conditions (ICs) Caron, 2013;Schumacher and Clark, 2014;Schwartz et al, 2015). The applied model perturbation methods range from a multiparameter approach (Gebhardt et al, 2011) to a stochastic physics scheme Romine et al, 2014) and to using different dynamical cores (Schumacher et al, 2013).…”

“…They mainly focus on the investigation of the impact of CP ensemble configurations, for example, the generation of IC perturbation, representation of the model error, uncertainties from the lateral boundary conditions (LBCs), ensemble size, and spatial scale (Kong et al, 2006;Clark et al, 2009Clark et al, , 2011Bouttier et al, 2012;Ben Bouallègue et al, 2013;Kühn-lein et al, 2014;Schwartz et al, 2015;Schumacher and Clark, 2014;Romine et al, 2014;Tennant, 2015). There are few comprehensive studies on the evaluation of CP EPS, in particular, in comparison with the mesoscale regional EPS.…”