Figure 9.1 The thunderstorms in this visible image taken July 30, 1999 do not pose the
major weather crisis occurring during this time. An intense heat wave of July killed over
200 people in the Midwest, which is predominately cloud free.
Figure 9.2 Cloud features seen in satellite imagery are used to identify fronts and track
their movements. This infrared satellite image shows a cloud system developing over the
North Pacific Ocean (to the left in the figure) and another approaching the west coast of
North America. Satellite observations are the best way to track storms over the oceans.
Figure 9.3 Major air mass source regions of the world. Observe the correlation between
the air source regions and surface high pressure systems shown in Figure 7.9.
Figure 9.4 The major air mass source regions that affect North American weather. The
arrows show the typical paths these air masses take once they begin to move. Which air
masses effect the weather where you live?
Figure 9.5 Weather associated with the combination of warm and cold can produce a noreaster. This infrared satellite image shows a nor'easter that ravaged the east coast during
January 7 and 8 1996. By the time the storm done, 3 feet of snow had accumulated in
several places, included Virginia and North Carolina. At least 86 people died because of
the weather associated with this storm. (A satellite image or weather map of a noreaster - I've got one on order).
Figure 9.6 Outbreaks of cold Canada cP air masses during early spring can result in bitter
cold temperatures as far south as Florida. (Photo of frozen fruit).
Figure 9.7 Arctic air masses are extremely cold. Jack London's character in To Build a
Fire, had to deal with the harsh conditions of A air masses. (Photo of frozen wasteland.)
Figure 9.8 High temperatures and dew points of a mT air masses can be very hazardous
in summer. The high temperatures and dew points of the heat wave in the Midwest
during the last two weeks of July 1999 were responsible for some 232 deaths.
(Midwesthern Climate Center)
Figure 9.9 Moisture supplied by mT air masses supply moisture for the summertime rains
of the southwestern United States. This seasonal precipitation cycle is referred to as the
Arizona Monsoon (Photo by Newman).
Figure 9.10 This infrared satellite image views the East Coast after the passage of cold
front associated with the Nor'eastern shown in Figure 9.5. As the cold and dry cP air
mass moves over the warm Gulf Stream, the air mass warms quickly and becomes
unstable. Mixing causes the low level clouds to form over the water.
Figure 9.11 A winter cP air mass that moves over a warmer body of warmer becomes
unstable as energy and moisture exchanges with the surface warm and moisten the lower
levels of the air mass.
Warm air mass
flows over
moving cold air mass
Cold air mass
Frontal zone
Frontal movement
Figure 9.12 A schematic three-dimensional representation of a front. (Merge these
figures, the bottom looks more 3-d but the top correctly describes the front as a
zone, not just a line. Make zone at the surface closer than in the upper atmosphere.)
Figure 9.13 A vertical slice through a cold and warm front, moving from right to left. The
dotted line is at a constant altitude from the surface. Notice the intersection of points D
and B with this altitude versus the surface frontal positions at locations C and A. The
smaller distance between C and D in comparison to the distance between A and B
demonstrates that the slope over the cold front is steeper than the slope of the warm front.
The slope of the cold front is 1:50 and is steeper than the warm front, 1:200.
Figure 9.14 Weather associated with a cold front, clockwise from upper left: a)
temperature, b) pressure, c) wind direction and d) precipitation. The L marks the location
of the lowest pressure. (Each panel should be the same size. Might want to draw an
arrow perpendicular to the front to emphasis changes as the front approaches - I
did this for upper left diagram. Then add to the legend "The bold arrow is a
reference that demonstrates how weather changes as a cold front is approached."
Also, move scattered thunderstorms ahead of the front.)
Figure 9.15 Vertical slice through a cold front. The steepness of the cold front favors the
development of thunderstorms.
Figure 9.16 Weather associated with a warm front, clockwise from upper left: a)
temperature, b) pressure, c) wind direction and c) precipitation. The lowest pressure is
marked with an L. (Might want to draw an arrow perpendicular to the front to
emphasis changes as the front approaches - I did this for upper left diagram. Then
add to the legend "The bold arrow is a reference that demonstrates how weather
changes as a cold front is approached.")
Ci
Cs
As
Ns
Warm
air mass
St
Cool air
Moderate, steady prec ipitation
Figure 9.17 Vertical structure along an ideal warm front.
Figure 9.18 Cloud types often observed along a stationary front.
mP
cP
Occluded front marked
at the surface.
mP
cP
Occluded front marked
at the surface.
Figure 9.19 The air mass behind the cold front can be colder or warmer than the air mass
ahead of the warm front. So, there are two idealized types: the a) cold-type and b) warmtype occluded fronts. (See Lutgens Figure 9-10 for better drafts and cloud and
precipitation.)
Figure 9.20 A surface and satellite image of an extratropical cyclone on 23 November
1999. The storm over the Midwest United States is an extratropical cylcone. Note how
the weather patterns associated with the warm and cold front are similar to our idealized
model.