These charts show the surface pressure pattern using isobars (lines of equal pressure) and indicate areas of high (H) and low pressure (L) along with their central pressure value. Isobars are represented by solid lines. High pressure is usually associated with settled weather while low pressure is normally associated with unsettled weather. Fronts are also displayed.
An analysis chart, which shows the observed state of the weather, is issued along with forecast charts out to five days ahead. These are updated every 12 hours around 0730 and 1930, with the exception of charts for days four and five which are only issued once per day at 1930. The reason that these two charts are only issued once a day is because that far ahead the forecast surface pressure pattern will change more significantly, due to uncertainty at this longer time period, and there is limited value in updating it every 12 hours.
Click on the appropriate time step on the timeline to view a chart for a particular time. You can also animate the charts by clicking on the play button.
A guide to interpreting weather charts can be found via the related links box.