1. Determine your elevation (meters or feet above sea level) by using
TABLE 1 or 2
below. The internet or an atlas
are also good sources to determine your elevation if the chart does not provide the correct information for your
general area (View section 27: Resources to look at).
2. Using the barometric tables (
TABLE 3 - TABLE 11
), find the table that is close to your current elevation:
TABLE 3 = 250 m above sea level
TABLE 8 = 1500 m above sea level
TABLE 4 = 500 m above sea level
TABLE 9 = 1750 m above sea level
TABLE 5 = 750 m above sea level
TABLE 10 = 2000 m above sea level
TABLE 6 = 1000 m above sea level
TABLE 11 = 2250 m above sea level
TABLE 7 = 1250 m above sea level
3. Once you have chosen the correct table, view the pressure reading on the HWS and run your finger along the
top of the table until the current pressure falls between the correct range.
4. Now view the outdoor temperature reading on the HWS and run your finger down the pressure column to
match the temperature range along the left side of the table.
5. Your finger now lays on the number of millibars (mb) you must add to the absolute pressure on the HWS display
to determine theoretical atmospheric pressure.
NOTE:
you must repeat the actions above every time there is a change in pressure, temperature or altitude to
retrieve the correct theoretical atmospheric pressure.
Example:
TORONTO, ON
Elevation (TABLE 1):
173 m above sea level
HWS current barometric pressure reading:
987.56 mb
HWS current outdoor temperature reading:
25ºC
a) Go to TABLE 3 (250m above sea level), which is the closest table to Toronto’s elevation.
b) Run finger along the top of table to reach 970-989.9 mb.
c) Run finger down chart to reach 16.0 to 25.9ºC.
d) Add 28.8 mb to the current pressure reading on HWS: 28.8 mb + 987.56 mb = 1, 016.36 mb
Theoretical Atmospheric Pressure =
1,016.36 mb*
*
Interesting Fact:
If your weather network provides you with kPa (or Kilopascals), divide the millibars (mb) by 10 (above Toronto example = 101.63 kPa)
TABLE 1: Elevation
of Major Cities
in Canada
18
Above Sea Level
City
Calgary, AB
Charlottetown, PE
Churchill Falls, NF
Edmonton, AB
Fredericton, NB
Halifax, NS
Iqaluit, NU
Montreal, QC
Ottawa, ON
Quebec City, QC
Regina, SK
m
1049
49
449
670
21
51
33
36
114
74
577
ft
3440
161
1443.20
2198
69
167
108
118
374
243
1893
City
Saskatoon, SK
Prince George, BC
St. John’s, NF
Thunder Bay, ON
Toronto, ON
Vancouver, BC
Victoria, BC
Whitehorse, YT
Winnipeg, MA
Yellowknife, NT
m
504
691
140
199
173
4
19
706
239
206
ft
1653
2266
459
653
567
13
62
703
784
676
Above Sea Level
NOTE:
The elevation in meters (m) and feet (ft) refers to the elevation of the
observing location above mean sea level according to Environment Canada:
http://www.climate.weatheroffice.ec.gc.ca/climateData/canada_e.html
Summary of Contents for Home Weather Station
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