North-West	North	North-East
West		East
South-West	South	South-East

TEMPERATURE

Vantage Pro Plus uses the Integrated Sensor Suite's (ISS) temperature sensor to measure the outside air temperature.  A second temperature sensor in the console measures the inside air temperature.

APPARENT TEMPERATURE MEASURES

The Vantage Pro Plus Weather Station at Gorge Creek Orchards calculates apparent temperature readings; wind chill and heat index:

WIND CHILL

Wind Chill takes into account how the speed of the wind affects our perception of the air temperature.  Our bodies warm the surrounding air molecules by transferring heat form the skin.  If there's no air movement, this insulating layer of warm air molecules stays next to the body and offers some protection from cooler air molecules.  However, wind sweeps that comfy warm air surrounding the body away.  The faster the wind blows, the faster the heat is carried away and the colder you feel.   At above 30°C wind movement has no effect on apparent temperature, so wind chill is the same as the outside temperature.

HEAT INDEX

The Heat Index uses the temperature and the relative humidity to determine how hot the air actually "feels".  When humidity is low, the apparent temperature will be lower than the air temperature, since perspiration evaporates rapidly to cool the body.   However, when the humidity is high (ie. the air is saturated with water vapour) the apparent temperature "feels" higher than the actual air temperature, because perspiration evaporates more slowly.

HUMIDITY

Humidity itself simply refers to the amount of water vapour in the air.  However, the amount of water vapour that the air can contain varies with the air temperature and pressure.  Relative humidity takes into account these factors and offers a humidity reading which reflects the amount of water vapour in the air as a percentage of the amount the air is capable of holding.   Relative Humidity, therefore, is not actually a measure of the amount of water vapour in the air, but a ratio of the air's water vapour content to it's capacity.  Vantage Pro Plus calculates and displays this relative humidity.

It is important to realise that relative humidity changes with temperature, pressure and water vapour content.  For example, a parcel of air with a capacity for 10g of water vapour which contains 4g of water vapour, the relative humidity would be 40%.  Adding 2g more water vapour (for a total of 6g) would change the humidity to 60%.  If that same parcel of air is warmed so that it has a capacity for 20g of water vapour, the relative humidity drops to 30% even though the water vapour content does not change.

DEW POINT

Dew Point is the temperature to which air must be cooled for saturation (100% relative humidity) to occur, providing there is no change in water content.  The Dew Point is an important measurement used to 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 vapour content, unlike relative humidity, which takes the air's temperature into account.   High Dew Point indicates high vapour content; low Dew Point indicates low vapour content.  In addition, a high Dew Point indicates a better chance of rain and severe thunderstorms.

You can even use Dew Point to predict minimum overnight temperature.  Provided no new fronts are expected overnight and the afternoon relative humidity >50%, the afternoon's Dew Point gives you an idea of what minimum temperature to expect overnight, since the air is not likely to get colder than the Dew Point anytime during the night.

RAINFALL

Vantage Pro Plus provides four separate registers for tracking rainfall totals: "rain storm", "daily rain", "monthly rain" and "yearly rain".  The Vantage Pro Plus also calculates the rate of rainfall by measuring the interval of time between each 0.254mm rainfall increment.

BAROMETRIC PRESSURE

The weight of 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 it is 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 Pro Plus Weather Station measures atmospheric pressure, but this is converted to barometric pressure because the altitude of the Gorge Creek Orchards Weather Centre (540m) has been entered into the station.  This essentially means that the Vantage Pro Plus has stored 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 pressure value is generally less important than the change in barometric pressure.  In general, rising pressure indicates improving weather conditions while falling pressure indicates deteriorating weather conditions.

A Stevenson Screen is a white boxed shelter that contains temperature and relative humidity equipment. It shields the instruments from sunshine and precipitations and has louvered sides to permit the free movement of air. The shelter is placed over grass, mounted 1 meter above the ground and as far from buildings as circumstances permit.

Climate refers to the average weather conditions at a specific place over a lengthy period of time (more than 30 years). The climate of a region plays a role in determining what agricultural crops can be grown in that region. The World Meteorological Organization, an agency of the United Nations, is responsible for the international exchange of weather data. It certifies that the data observation procedures do not vary among the over 130-nation participants.

Temperature refers to how hot or cold the atmosphere is as measured by a thermometer (in Celsius (C) or Fahrenheit (F), or Kelvin (K) ). A traditional thermometer consists of mercury, red spirit or green spirit in a glass tube and operates on the principle that the liquid expands more that the glass does when heated. Digital electronic devices can also be used were the unit can record the max and min temperature reached and some units can store a series of data (a data logger) and others transmit an electronic signal measuring temperature back to a second temperature display on a PC or a base. These new probes can also be used to measure soil temperature.

Atmospheric Pressure - the weight of the atmosphere overhead (the force exerted on a unit area, such as a square centimeter, by the mass of the atmosphere as gravity pulls it to earth) - expressed in millibars of inches of mercury. Commonly measured with a mercury barometer, a glass tube in which the height of a column of mercury fluctuates as the weight of the atmosphere changes. Changes in atmospheric pressure signal shifts in the weather and can be measured with a simple dial barometer.

Humidity refers to the amount of water vapour the air contains. (Expressed as relative humidity, or the amount of water vapour air contains expressed as a percentage of the maximum amount it can hold at the same temperature). Cool air holds less water than warm air.

Measuring Humidity; A Psychrometer is an instrument used to measure relative humidity. It traditionally consists of two thermometers, one covered with a wet cloth. Evaporation cools this thermometer below the actual air temperature, recorded on the dry thermometer. Evaporation and cooling depends on how dry the air is at a given temperature. A table can be used to determine the relative humidity from the amount of cooling. Digital electronic instruments (hygrometers) can be used for quick readings and more upmarket units offer data logging. Some instruments offer a simple dial readying of Relative Humidity, while these offer the least accuracy they can be used as a good indication.

Growing Degree Day (or Heat Units) - a measure of the departure of the mean daily temperature above or below a given standard. Information can be used to optimize timing of planting, fertilizing, pesticide application and harvesting.

Growing Season - the period of the year when crops and other plants grow successfully. Calculated by the average number of days between the last heavy frost in spring and the first severe frost in autumn. The length of the growing season varies from place to place and partially determines what crops can be grown in an area.

Precipitation is a term that covers all of the forms in which water falls to earth from the atmosphere. Main types: rain, snow, sleet and hail. Precipitation is life-sustaining - its amount and distribution a regions receives plays a major role in determining what can survive there and what plants can be grown.

A tipping bucket is an instrument used to measure precipitation. It contains a dual-chamber mini-collection bucket located beneath a collection funnel. When precipitation fills one side of the bucket, gravity empties it and sends a signal to the data logger. Some tipping buckets are equipped with internal heaters to melt snow and frozen rain.

Simple rain gauges. Basically, any measuring glass left outside can serve as a rain gauge. However, since most rain showers are usually quite windy, you'll want to fasten your rain gauge somewhere so that it doesn't blow over. Locate a good place for your gauge. There should be nothing overhead, like trees, electric wires, or the edge of a roof. These obstructions can direct rainwater into or away from your gauge, creating a false reading. The edge of a fence, away from the building, is often a good place for your gauge. Tip: A ring of slated metal around the perimeter of the rain gauge provides a wind shield to decrease splash and wind-induced errors. Once you have found the spot, attach a holding rack. Then, slip your measuring glass into position. Wait for rain, then record your measurement, and empty the glass.

Rain refers to liquid precipitation that falls from clouds as drop 0.5 millimeters in diameter or larger. Drizzle consists of drops smaller than 0.5mm.

Hail originates when colliding drops of water freeze together in the cold upper regions of a thunderstorm. Hail can cause considerable damage to agricultural regions, depending on the size and intensity of the hail storm. At 12:15, May 30, 1985 45 cm of hail fell in the Leamington area causing damage to plants and greenhouses.

Drought refers to a prolonged period of greatly reduced precipitation. Droughts can last a few weeks (in which case they are called dry spells) or months, or even years.

Frost refers to the white coating of ice crystals you often see on or near the ground after a cold night. Frost occurs through a process called sublimation where a gas, such as water vapour, becomes a solid, or when a solid becomes a gas without first becoming a liquid. (i.e. a leaf losses heat during the night. If the leaf's temperature falls below 0 C, water vapour in the surrounding air will freeze on it. Fruit growers are concerned about "killing frosts". (Temperatures that are far enough below freezing to harm cold-sensitive plants such as peach trees

Wind is the movement of air. It arises because of differences in temperature and atmospheric pressure between nearby regions of the earth. Winds tend to blow from areas of high pressure to areas of low pressure. It is one of the weather's most changeable forces. It can change form a light breeze to a fierce storm within a short time. Wind has been carefully measured for centuries

  Beaufort Scale - Wind Speed & Observed Effects

Force	Knots	Mph	Kph	Sea Term	Sea Conditions	On-land Appearance
0	<1	<1	<1	Calm	sea like a mirror	smoke rises vertically
1	1-3	1-3	1-6	Light air	ripples with appearance of scales: no foam crests	smoke drifts and leaves rustle
2	4-6	4-7	7-11	Light breeze	small wavelets: crests of glassy appearance, not breaking	wind felt on face
3	7-10	8-12	12-19	Gentle breeze	large wavelets: crests begin to break: scattered whitecaps	flags extended, leaves move
4	11-16	13-18	20-30	Moderate breeze	small waves, becoming longer: numerous whitecaps	dust and small branches move
5	17-21	19-24	31-39	Fresh breeze	moderate waves, taking longer form: many whitecaps: some spray	small trees begin to sway
6	22-27	25-31	40-50	Strong breeze	larger waves forming: whitecaps everywhere: some spray	large branches move, wires whistle
7	28-33	32-38	51-61	Near gale	sea heaps: white foam from breaking waves begins to be blown in streaks	trees in motion, resistance felt when walking
8	34-40	39-46	62-74	Gale	moderately high waves of greater length: edges of crests begin to break into spindrift: foam is blown in well-marked streaks	walking impeded
9	41-47	47-54	75-87	Strong gale	high waves: sea begins to roll: dense streaks of foam: spray may reduce visibility	structural damage may occur
10	48-55	55-63	88-102	Storm	very high waves with overhanging crests: sea takes white appearance as foam is blown in very dense streaks: rolling is heavy and visibility is reduced	trees uprooted, structural damage likely
11	56-63	64-72	103-117	Violent Storm	Exceptionally high waves: sea covered with white foam patches: visibility still more reduced	damage to structures wide spread
12	>63	>72	>117	Hurricane	air filled with foam: sea completely white with driving spray: visibility greatly reduced	severe structural damage to buildings, wide spread devastation, flooding