Relating pressure to mountain elevations
Learning goal 6n: Relate pressure levels to ski areas and mountain elevations across southern BC.
We can use pressure-level maps to look at weather
variables at heights above sea-level elevation. Remember that air
pressure decreases as height increases. To better picture the
height at which different pressure levels are located,
we'll relate them to mountains and ski areas in BC. But first, what are
the different mountain ranges in BC and where are they located?
Fig. 6n.1 - The mountain ranges of British Columbia
(BC). (Credit: Google/West)
Look at Fig. 6n.1. Starting in the west are the Coast Mountains; the
North Shore Mountains immediately north of Vancouver are at the
southern extent of the range. Moving eastwards across the southern BC
Interior (the Interior is anything east of the Coast Mountain range),
there are the Cariboo and Monashee ranges, followed by the Selkirks and
Purcells - these four are collectively referred to as the Columbia
Mountain range. Finally the Rocky Mountains fall along the BC/AB
border.
Pressure units
Commonly used units of atmospheric pressure are kilopascals (kPa) and hectopascals (hPa) . An older, outdated pressure unit is millibars (mb).
- 1 kPa = 10 hPa = 1000 pascals (Pa)
- 1 hPa = 1 mb = 100 Pa
In modern scientific journal papers and on forecast maps from UBC
you
will more likely see kPa. However, hPa and mb were more traditionally
used in meteorology last century, so you can expect to see these on
other pressure maps that you might come across.
Pressure at sea level is typically around 100.0 kPa (1000 hPa, ~0 m
elevation, see Fig. 6n.2). Moving upward through the atmosphere, the
next level that meteorologists usually care about and plot weather maps
for is 85.0 kPa, which is around 1500 m (~5000 ft). The 85.0-kPa level
is a couple of hundred metres above the North Shore Mountain peaks
(Fig. 6n.1);
these are the mountains you see looking north from downtown such as
Grouse and Cypress.
85.0 kPa is also about mid-mountain at Whistler, which is in the
Coast
Mountains (Fig. 6n.1). Usually when skiers say "mid-mountain" they mean
the middle section of the skiing elevation range. Moving higher still,
the next level is 70.0 kPa. This is at about ~3000 m (or 10,000 ft),
which is just above the height of the top of the tallest mountains in
Southwest BC (e.g. Skihist, Matier, and Wedge, not shown in Fig. 6n.2).
Whistler, and most ski resorts in the Interior ranges, peak at
around
2000-2300 m (6500-7500 ft). Mount Sir Donald (Fig. 6n.2) is a popular
backcountry
ski area in the Selkirks, with a peak at ~3300 m. There are other peaks
outside of ski areas in the Interior that also exceed 3000 m.
Ski resorts in the Rockies peak at anywhere between 2000-2800 m
(6500-9500 ft), e.g. Lake Louise. The highest peaks in the Rockies are
around 3500 m, but the very highest, Mount Robson, is almost 4000 m
(13000 ft).
Fig. 6n.2 - Elevations and approximately equivalent
pressure levels as they relate to various ski resorts and backcountry
areas across southern and central BC and AB. White triangles represent
typical skiing elevations. All elevations are elevations above sea
level. (Credit: West)
Pressure-level maps lower in the atmosphere than 50.0 kPa (~5500 m),
which is higher than most mountain peaks, fall in the category of low-level
maps. Meteorologists also use upper-level maps, which
refer to pressure levels ranging from 50.0 kPa to the top of the
troposphere (the tropopause) at around 25.0 kPa (~10500 m). This tells
them more advanced information about the upper atmosphere, but we won't
get into those in this course.
Keywords: pressure-level maps, kilopascals, hectopascals
Figure Credits: Stull: Roland Stull, West:
Greg West, Howard: Rosie Howard