Model: Global weather forecast model from the "European Centre for Medium-Range Weather Forecasts" Update: 10:00 GMT und 23:00 GMT Greenwich Mean Time: 12:00 GMT = 13:00 BST Variable: Sea Level Pressure Description: The surface chart (also known as surface synoptic chart) presents the distribution of the atmospheric pressure observed at any given station on the earth's surface reduced to sea level. You can read the positions of the controlling weather features (highs, lows, ridges or troughs) from the distribution of the isobars (lines of equal sea level pressure). The isobars define the pressure field. The pressure field is the dominating player in the weather system. Additionally, this map helps you to identify synoptic-scale waves and gives you a first estimate on meso-scale fronts.