Since 2007, meteorologists of the U.S. Army Test and Evaluation Command (ATEC) at Dugway Proving Ground (DPG), Utah, have relied on a mesoscale ensemble prediction system (EPS) known as the Ensemble Four-Dimensional Weather System (E-4DWX). This article describes E-4DWX and the innovative way in which it is calibrated, how it performs, why it was developed, and how meteorologists at DPGuse it. E-4DWX has 30 operational members, each configured to produce forecasts of 48 h every 6 h on a 272-processor high performance computer (HPC) at DPG. The ensemble's members differ from one another in initial-, lateral-, and lower-boundary conditions; in methods of data assimilation; and in physical parameterizations. The predictive core of all members is the Advanced Research core of the Weather Research and Forecasting (WRF) Model. Numerical predictions of the most useful near-surface variables are dynamically calibrated through algorithms that combine logistic regression and quantile regression, generating statistically realistic probabilistic depictions of the atmosphere's future state at DPG's observing sites. Army meteorologists view E-4DWX's output via customized figures posted to a restricted website. Some of these figures summarize collective results-for example, through means, standard deviations, or fractions of the ensemble exceeding thresholds. Other figures show each forecast, individually or grouped-for example, through spaghetti diagrams and time series. This article presents examples of each type of figure.

A variety of high-resolution atmospheric-model applications are running on the high performance computer cluster at Dugway Proving Ground (DPG), with the objective of providing accurate weather information to forecasters, test managers and planners, and decision-support staff at ATEC test ranges. The foundation of these applications is the 4D Weather (4DWX) forecasting system, which is built upon the Real-Time Four Dimensional Data Assimilation (RTFDDA) process and the Weather Research and Forecasting (WRF) and Penn State University/NCAR Mesoscale Model version 5 (MM5) forecasting models. The RTFDDA has been expanded for generating ensemble analyses and probabilistic forecasts (the E-RTFDDA system), and a 30-member E-RTFDDA system has been implemented and operated on the HPC cluster at DPG since August 2007. The system contains three nested domains with a fine mesh having a 3.3-km grid increment. The system generates 48-h forecasts every 6 hours. E-RTFDDA design features, capabilities, and real-time operation at DPG are introduced. This application, crucially depending on high performance computerpsilas computing power, is unique advanced technology that can serve as a national asset to support homeland security and homeland defense.

Dugway Terrain: DPG is located in the Great Basin area of western Utah, south of the Great Salt Lake, with nearly 800,000 acres of desert conditions. The terrain combines large areas of relatively flat ground, with a few isolated mountain ranges extending about 1000m above the range floor. The ground surface includes patchy low vegetation, dry sandy soil, and salty playas.