CHPT. 2: DRAWING ISOBARS ON A WEATHER MAP

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Surface weather maps have isobars drawn around high and low pressure systems. (Isobars are lines of equal pressure). Here are the rules.

1.
See
if you can locate the high and low pressure systems. High pressure systems have the highest pressure in the center of
the system. Look for such pressures as 1016.0 or 160, 1020.0 or 200, 1024 or
240, 1028 or 280 etc.

2.
Low
pressure systems have the lowest pressure in the center of the system. Look for pressures such as 1000.0 or 000, 996.0
or 996.0, 992.0 or 920, 988.0 or 880, 984.0 or 840, 980.0 or 800 etc.

3.
If
you are analyzing a high pressure system, first look for the highest pressure
you can find on the map. For example, you find a station that has a pressure of
290. An isobar is not drawn for 290 but
one is drawn for 280. That is our first
isobar. Since 290 is higher than 280,
it must be kept inside (toward higher pressure) the 280 isobars. Everything lower than 280 must be kept
outside (toward lower pressure) the 280 isobar. If you see a 270 near a 290 the 280 isobar goes right between the
two readings. The next isobar you will draw is the 240. Again, everything higher than 240 must go
inside (Toward higher pressure) the 240 line. All pressures lower than 240 must
go outside the 240 isobar. Next draw the 200 isobar. Again, all pressures
higher than 200 must stay on the inside of the 200 isobar, all pressure lower
than 200 must stay on the outside of the 200 isobar.

4.
Label
the center of the system with a large blue “H” for high pressure and the system
is complete.

Now
let’s analyze a low pressure system. In
this case you look for the lowest pressures on the map. You find an 842. No
isobars are drawn for 842but one is drawn for 844. Since 842 is lower than 844,
the 842 must be kept on the inside (toward lower pressure) of the 844. Next isobar is the 880. All pressures lower
than 880 must be kept on the inside (toward lower pressure) of the 880 isobar
while pressure higher than 880 must be kept outside the 880 isobar. Next look for
the 992 pressure reading. Again lower pressure inside the 992 isobar, higher
pressures outside. When you are finished, label the center of the system with a
large red “L”.

Try
to analyze the three pressure systems below.
Read the directions carefully.

Link to pressure1

Link to pressure2

Link to pressure3--------------------------------------------
Link to answer 3