Computer generated chart that depicts analyzed 500 mb heights and is generated twice a day from the NCEP global forecast computer model run. These products depict synoptic scale flow with troughs subjectively analyzed for significant long and short waves associated with 24 hour surface lows. Trough's analyzed may not always be consistent with the underlying forecast 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.