Figure 16.44: Different types of weather that can be shown using a weather symbol. ( 23 )Weather maps can have many types of connecting lines. For example:
- Lines of equal temperature are calledisotherms. Isotherms show temperature gradi-
ents and can indicate the location of a front. The 0°C (32°F) isotherm will show where
rain is likely to give way to snow. - Isobarsare lines of equal average air pressure at sea level (Figure16.45). Closed
isobars represent the locations of high and low pressure cells. High pressure cells are
shown asH’s and low pressure cells asL’s. A thick, brown dashed line is often placed
inside a long low pressure trough. - Isotachsare lines of constant wind speed. Where the minimum values occur high in
the atmosphere, tropical cyclones may develop. The highest wind speeds can be used
to locate the jet stream.
Surface weather analysis maps are weather maps that only show conditions on the ground
(Figure16.46). These maps show sea level mean pressure, temperature and amount of cloud
cover. This information will reveal features such as high and low pressure cells.
Weather maps can also depict conditions at higher altitudes. Aviation maps show conditions
in the upper atmosphere, particularly those that are of interest to pilots. These include
current weather, cloud cover, and regions where ice is likely to form.