DAVIS Weather Envoy (6316, 6316C) - Manual (Page 25)

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predict the formation of dew, frost, and fog. If dew point and temperature
are close together in the late afternoon when the air begins to turn colder,
fog is likely during the night. Dew point is also a good indicator of the
air’s actual water vapor content, unlike relative humidity, which takes the
air’s temperature into account. High dew point indicates high water vapor
content; low dew point indicates low water vapor content. In addition a
high dew point indicates a better chance of rain, severe thunderstorms,
and tornados.
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.
Dew Point is equal to the air temperature when the Humidity is 100%.
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
increment or 0.2 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 means that atmospheric pressure changes with altitude. For
example, atmospheric pressure is greater at sea level than on a
mountaintop. 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 atmospheric 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 forecasting purposes, however, the absolute barometric