Again, the choice is yours. Many analysts like to begin with a specific isobar, the 1016 often being preferred. They feel it outlines more pressure systems than any other isobar when completed. Others may choose a value that is well defined by the reports in the area. Note that of the seven re-ports in this area, only one has the exact pressure of 1012.0 mb.
Interpolation is a fitting and placement pro-cess.
When the exact value of the isobar you ve chosen to draw isn t reported, you must inter-polate its location between stations. For ease of understanding, let s look at our example again. Moving downwind from point A, you first come to two stations that are reporting sea level pressures of 1011.2 mb and 1013.2 mb. As the analyst, you must decide on its placement. Situation requiring interpolation between pressures.