We'll follow the same procedure that we did for the cold front
example.
Step #1
We'll start by drawing some isobars to map out the pressure
pattern. A partial list of allowed isobars is shown at the
right side of the map above (increments of 4 mb starting at 1000
mb). We've located located the highest and lowest pressure
values on the map. Then we choose allowed isobar values that
fall between these limits. In this case we'll need to draw
992 mb and 996 mb isobars.
Here's the map with color coded pressures. Pressures less
than 992 mb are purple,
pressures between 992 and 996 mb are blue,
and pressures greater than 996 mb are green.
Note that station B has a pressure of exactly 992.0 mb, the 992 mb
isobar will go through that station. The 996 mb isobar will
go through station A because it has a pressure of exactly 996.0
mb.
Here's the map with the isobars drawn in. On the map below
we use colors to locate the warm and cooler air masses.
Step #2
The warm air mass has been colored in orange. Cooler air
east of the low pressure center is blue. Can you see
where the warm front should go?
Step #3
Here's the map with a warm front drawn in (the map was redrawn so
that the edge of the warm (orange) air mass would coincide with
the warm front). The change in wind directions was probably
more noticeable that the temperature change. Most of the
cloud outlined in green are probably being produced by the warm
front. You can see how more extensive cloud coverage is with
a warm front.
Step #4
Two of the stations near the right edge of the picture and on
opposite sides of the front are redrawn below.
The station north of the front has cooler and drier air, winds are
from the east, skies are overcast and light rain is falling.
The pressure is falling as the warm front approaches. These
are all things you'd expect to find ahead of a warm front.
Behind the front at the southern station pressure is rising, the
air is warmer and moister, winds have shifted to the south and the
skies are starting to clear.
Step #5
Finally it's worth looking at the left, western, side of the
map. There's pretty good evidence of a cold front.
There's a big temperature change (low 60s to low 40s and 30s)
and a very noticeable wind shift (SW ahead of the cold front and
NW behind).
