ATSC 113 Weather for Sailing, Flying & Snow Sports


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?

mtnRanges

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  An older, outdated pressure unit is millibars (mb).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).

mtnPres

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