Geoscience Reference
In-Depth Information
Estevan Point (6m)
49°N, 127°W
mm
400
300
200
Kamloops (366m)
51°N, 120°W
100
mm
50
0
0
J
FM
A
M
J
J
A
S O N D
J
FM
A
M
J
J
A
S O N D
Glacier (1250m)
51°N, 117°W
mm
Calgary (1128m)
51°N, 114°W
200
mm
100
100
50
0
0
J
FM
A
M
J
J
A
S O N D
J
FM
A
M
J
J
A
S O N D
Figure 10.16
Precipitation graphs for stations in western Canada. The shaded portions represent
snowfall, expressed as water equivalent.
Washington) and the Coast Range (in British
Columbia), but summers are drier due to the
strong North Pacific anticyclone. The regime in
the interior of British Columbia is transitional
between that of the coastal region and the
distinct summer maximum of central North
America (Calgary), although at Kamloops in the
Thompson valley (annual average 250mm) there
is a slight summer maximum associated with
thunderstorm-type rainfall. In general, the
sheltered interior valleys receive less than 500mm
per year. In the driest years certain localities
have recorded only 150mm. Above 1000m, much
of the precipitation falls as snow (see
Figure 10.16
)
and some of the greatest snow depths in the world
are reported from British Columbia, Washington
and Oregon. A US national record seasonal total
of 28.96m was observed in 1998-1999 at the
Mt. Baker, WA, ski area, where the annual mean
amount is 16.4m. Generally, 10-15m of snow
falls annually on the Cascade Range at heights of
about 1500m, and even as far inland as the Selkirk
Mountains snowfall totals are considerable.
The mean snowfall is 9.9m at Glacier, British
Columbia (elevation 1250m), and this accounts
for almost 70 percent of the annual precipitation
(see
Figure 10.16
). Near sea level on the outer
coast, in contrast, very little precipitation falls as
snow (for example, Estevan Point). It is estimated
that the climatic snowline rises from about 1600m
on the west side of Vancouver Island to 2900m in
the eastern Coast Range. Inland, its elevation
increases from 2300m on the west slopes of the
Columbia Mountains to 3100m on the east side of
the Rockies. This trend reflects the precipitation
pattern referred to above.
