Geoscience Reference
In-Depth Information
Artctic
Ocean
air
North
Atlantic
air
ic
75
%
100°
90°
80°
Figure 10.15
Regions in North America east of the Rocky Mountains dominated by the various air-mass
types in July for more than 50 percent and 75 percent of the time. The 50 percent frequency lines
correspond to mean frontal positions.
Source: After Bryson (1966).
extension of the drift to high latitudes (see
Figure
7.29
).
The Pacific coast ranges greatly restrict the
inland extent of oceanic influences, and hence
there is no extensive maritime temperate climate
as in Western Europe. The major climatic features
duplicate those of the coastal mountains of
Norway and those of New Zealand and southern
Chile in the belt of southern westerlies. Topo-
graphic factors make the weather and climate
of such areas very variable over short distances,
both vertically and horizontally. A few salient
characteristics are selected for consideration
here.
There is a regular pattern of rainy windward
and drier lee slopes across the successive north-
west to southeast ranges, with a more general
decrease towards the interior. The Coast Range in
British Columbia has mean annual totals of
precipitation exceeding 2500mm, with 5000mm
in the wettest places, compared with 1250mm or
less on the summits of the Rockies. Yet even on the
leeward side of Vancouver Island, the average
figure at Victoria is only 700mm. Analogous to
the 'westerlies-oceanic' regime of northwest
Europe, there is a winter precipitation maximum
along the littoral (Estevan Point in
Figure 10.16
),
which also extends beyond the Cascades (in
