How the Weather is Recorded
in
Armidale NSW
How is the weather measured in Armidale and what instruments are used?
The Bureau of Meteorology
weather station is located in
Temperature
Temperatures are measured with mercury and alcohol thermometers which are read
by observers at designated observation times daily. These thermometers are very
accurate measuring the temperature in tenths of degrees.
They are housed within a Stevenson Screen which is a white painted timber box
with louvred sides with the base about 1.1 metres above the ground. The louvres
allow outside air to move slowly past the instruments while protecting them
from direct sunlight, wind and rain, and temperatures recorded this way are
referred to as screen or shade temperatures.
Mercury thermometers supply current dry and wet bulb temperatures.
A mercury thermometer records the maximum temperature for the 24 hours
to
An alcohol thermometer records the minimum temperature for the 24 hours
to
A thermograph records the temperature continuously onto a seven day
graph which is used to determine the times at which maximum and minimum
temperatures occur.
An alcohol minimum thermometer is placed on the surface of the grass each
evening to record the overnight terrestrial or grass minimum
temperature. The terrestrial minimum is usually between 2 and 5 degrees lower
than the screen minimum.
Rainfall
Rainfall is recorded with a rain gauge set in the ground with the top 30 centimetres above the ground. It consists of a metal drum
with a funnel 203 millimetres in diameter and a plastic measuring cylinder
within. Rainfall is totaled for the 24 hours ending
Evaporation
This is measured using an American Class A pan 1206 millimetres in diameter and
250 millimetres deep. At
Wind
A wind vane mounted to a ten metre tower is used to
determine the wind direction to 16 points of the compass. A cup anemometer,
also mounted to the tower, is used to calculate the wind speed and the wind run
for the 24 hour period ending at
Cloud
Details on clouds including amount of cloud covering the sky in eighths, height
of clouds, and the type of clouds are observed and recorded.
Visibility
Horizontal visibility is estimated. This is reduced by precipitation, fog, and
on some winter mornings and evenings by Armidale's woodsmoke haze trapped in the valley.
Phenomena
Other aspects of the weather referred to as phenomena are also recorded. These
include: frosts, fogs, hail, snow, thunderstorms and strong winds.
The BOM
AIRPORT
WEATHER STATION
The Bureau of Meteorology also operates an automatic weather station at
Manually operated weather stations, such as the East Armidale weather station, continue to remain a part of the Bureau network as human observers can observe and report conditions that automatic weather stations are unable to do, such as details of clouds, thunderstorms, hail (size and quantity of hailstones) and snowfalls (depth of snow on ground).
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