45
You can also use dew point to predict the minimum overnight temperature.
Provided no new fronts are expected overnight and the afternoon Relative
Humidity is greater than or equal to 50%, the afternoon’s dew point gives
you an idea of what minimum temperature to expect overnight, since the
air can never get colder than the dew point.
Rain
Vantage Pro2 incorporates a tipping-bucket rain collector in the ISS that
measures 0.01'' for each tip of the bucket. A metric adapter can be installed
to measure 0.2 mm for each tip of the bucket.Your station logs rain data in
the same units it is measured in and converts the logged totals into the
selected display units (inches or millimeters) at the time it is displayed.
Converting at display time reduces possible compounded rounding errors
over time.
Four separate variables track rain totals: “rain storm”, “daily rain”,
“monthly rain”, and “yearly rain”. Rain rate calculations are based on the
interval of time between each bucket tip, which is each 0.01'' rainfall incre-
ment or .2 mm.
Barometric Pressure
The weight of the air that makes up our atmosphere exerts a pressure on
the surface of the earth. This pressure is known as atmospheric pressure.
Generally, the more air above an area, the higher the atmospheric pressure,
this, in turn, means that atmospheric pressure changes with altitude. For
example, atmospheric pressure is greater at sea-level than on a mountain-
top. To compensate for this difference and facilitate comparison between
locations with different altitudes, atmospheric pressure is generally
adjusted to the equivalent sea-level pressure. This adjusted pressure is
known as barometric pressure. In reality, the Vantage Pro2 measures atmo-
spheric pressure. When you enter your location’s altitude in Setup Mode,
the Vantage Pro2 stores the necessary offset value to consistently translate
atmospheric pressure into barometric pressure.
Barometric pressure also changes with local weather conditions, making
barometric pressure an extremely important and useful weather forecasting
tool. High pressure zones are generally associated with fair weather while
low pressure zones are generally associated with poor weather. For fore-
casting purposes, however, the absolute barometric pressure value is gen-
erally less important than the change in barometric pressure. In general,
rising pressure indicates improving weather conditions while falling pres-
sure indicates deteriorating weather conditions.
Solar Radiation
What we call “current solar radiation” is technically known as Global
Solar Radiation, a measure of the intensity of the sun’s radiation reaching a
horizontal surface. This irradiance includes both the direct component
07395.234 Manual VP2 console Book.book Page 45 Wednesday, November 17, 2004 3:57 PM
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