The weather maps used by forecasters fall into two main groups. Maps that show what was happening at a specific time in the past are called analyses. Maps that show what is expected to happen at a particular time in the future are called prognoses. Both types can be prepared to show conditions either at ground level or at different heights in the atmosphere. Forecasters need to know not just how warm or cold it is on the ground and where it's raining or snowing; they also have to know what's going on above us--is there a lot of moisture up there? or what's happening with the winds high above us that steer our weather systems?
The weather map that most people are familiar with is the surface analysis--a map like the one on the left showing isobars, warm and cold fronts, and high and low pressure systems. On this particular map, areas of continuous precipitation have been shaded in green, and the brown scalloped line shows cloud cover. Special high-speed printers produce surface weather maps 4 times a day, at 6-hour intervals. If you'd like to see this morning's weather map, just follow use Environment Canada's weather Web site. Can you find your location? Are you in an area of high pressure or low pressure today?
Prognostic charts (sometimes called "progs" or forecast charts) can be as simple as the map with icons that you might see in a newspaper or on our Web site.
- Date modified: