Contour lines are drawn on just about any weather chart, including pressure charts, temperature charts, dewpoint charts, analysis charts, model graphics, etc. There are particular rules that contour lines typically follows. Below are the particular rules: 1) Contour lines do not cross over each other 2) Contour lines do not merge 3) Contour lines do not split apart 4) Contour lines typically do not have discontinuities (sharp edges). There are exceptions to this when the resolution is not fine enough to show curvature or when there is a sudden discontinuity from a front or another boundary where there is a sudden change in the variable being contoured. Discontinuities or “kinking” can occur along an air mass boundary, pressure contours crossing a frontal boundary, or over strong density gradients. 5) Contour lines are not extrapolated into regions that have no data. Contour lines within a region of no data are a “best guess” but could be very wrong. Contour lines typically have smooth curvature. Contour lines can and commonly do close off into circles. Contour lines stop when they reach the edge of the chart or at the edge of where data is present. The diagrams below show characteristics that contour lines typically do not have and then there is a diagram of how they typically look.   |