Computer generated chart that depicts analyzed 500 mb heights and is generated twice a day from NCEP model forecast guidance. These products depict synoptic scale flow with troughs subjectively analyzed for significant long and short waves associated with surface lows. Trough's analyzed may not always be consistent with the underlying analysis because of the automated nature of the analysis. The contour interval is depicted for intervals of 60 meters. Wind barbs indicate wind direction and speed in knots.