 BAROMETRIC PRESSURE
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. Barometric pressure changes with local weather conditions, making barometric pressure an 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, 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. |
CLOUD HEIGHT
The cloud height on this site is an estimate of cumulus clouds using a formula based on temperature and dew point. Actual measurements of cloud height are made with a ceilometer. This device fires a laser into the sky and measures the backscattered signal. Costs for such a device are beyond the scope of weather hobbyists. |
METAR
Acroymn for METeorological Aerodrome Report. It is the primary observation code used in the United Kingdom to satisfy requirements for reporting surface meteorological data. Minimum reporting requirments includes wind, visibility, runway visual range, present weather, sky condition, temperature, dew point, and altimeter setting. |
DEW POINT
Dew point is the temperature to which air must be cooled for saturation to occur. 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 vapor content, unlike relative humidity, which takes the air's temperature into account. High dew point indicates high vapor content; low dew point indicates low vapor content. In addition a high dew point indicates a better chance of rain and severe thunderstorms. You can even use dew point to predict the minimum overnight temperature. Provided no fronts or other weather pattern changes are expected overnight, the afternoon's dew point gives you an idea of what minimum temperature to expect overnight |
HUMIDITY
Humidity or relative humidity measures the amount of water vapor in the air relative to the temperature. It is important in weather because humidity affects how humans feel. A hot, humid day feels hotter because we cannot sweat as effectively. A cool, dry day feels colder because moisure evaporates more easily. |
HEAT INDEX
The Heat Index is a measure of relative discomfort due to combined heat and high humidity. It was developed by R.G. Steadman (1979) and is based on physiological studies of evaporative skin cooling for various combinations of ambient temperature and humidity. As temperatures climb above 90 °F and humidity goes above 40 percent, conditions are ripe for heat-related illnesses.
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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. The irradiance includes both the direct component from the sun and the reflected component from the rest of the sky. The solar radiation reading gives a measure of the amount of solar radiation hitting the solar radiation sensor at any given time, expressed in Watts/sq. meter (W/m2).
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UV (ULTRA VIOLET) RADIATION
Energy from the sun reaches the earth as visable, infared and ultraviolet (UV) rays. Exposure to UV rays can cause numerous health problems, such as sun burn, skin cancer, skin ageing, cataracts and can suppress the immune system. The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of absorption in the atmosphere's ozone layer, 99% of the ultraviolet radiation that reaches the Earth's surface is UVA. (Some of the UVC light is responsible for the generation of the ozone.) A positive effect of UV light is that it induces the production of vitamin D in the skin.
| UV Index |
Description |
Media Graphic Color |
Recommended Protection |
| 0–2 |
Low danger to the average person |
Green |
Wear sunglasses; wear sunscreen if there is snow on the ground, which reflects UV radiation, or if you have particularly fair skin. |
| 3–5 |
Moderate risk of harm from unprotected sun exposure |
Yellow |
Wear sunglasses and sunscreen, cover the body with clothing and a hat, and seek shade around midday when the sun is most intense. |
| 6–7 |
High risk of harm from unprotected sun exposure |
Orange |
Wear sunglasses and sunscreen having SPF 15 or higher, cover the body with clothing and a wide-brim hat, and reduce time in the sun from two hours before to three hours after solar noon (roughly 11:00 to 16:00 during summer in zones that observe daylight saving time). |
| 8–10 |
Very high risk of harm from unprotected sun exposure |
Reddish-purple |
Same precautions as above, but take extra care — unprotected skin can burn quickly. |
| 11+ |
Extreme risk of harm from unprotected sun exposure |
Violet |
Take all precautions, including: wear sunglasses and sunscreen, cover the body with a long-sleeve shirt and pants, wear a broad hat, and avoid the sun from two hours before to three hours after solar noon. |
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WEATHER STATION
A weather station is a facility with instruments and equipment to make weather observations by monitoring atmospheric conditions to study the weather. This weather station has a thermometer for measuring temperature; barometer for measuring changes in air pressure; hygrometer for measuring humidity; anemometer for measuring wind speed and wind direction; and rain gauge for measuring precipitation. My station also has non-traditional equipment like a webcam for visual weather observation and an electro-magnetic pulse counter for lightning
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WIND CHILL
The wind chill temperature is what the temperature "feels like" to people and animals during cold weather. Wind chill is based on the rate of heat loss from exposed skin caused by wind and cold. As the wind increases, it draws heat from the body, driving down skin temperature and eventually the internal body temperature. Once temperatures drop below 10 °F and the wind is gusting, conditions are ripe for cold-related illnesses. Below -5 °F, any wind is a major factor in frostbite and hypothermia.
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BEAUFORT WIND SCALE
The is named after Sir Francis Beaufort, an admiral in the British Navy. He developed the scale in 1805 in order to estimate wind speed by noting how sails move in the wind. It turned out to be a great help and was later adapted for use on land.
Force 0
Strength: Calm
Speed: Less than 1 mile per hour (mph), less than 2 kilometers per hour (kph)
Observations: Tree leaves don't move, smoke rises vertically, sea is calm
Force 1
Strength: Light Air
Speed: 1-3 mph, 2-6 kph
Observations: Tree leaves don't move, smoke drifts slowly, sea is lightly rippled
Force 2
Strength: Slight Breeze
Speed: 4-7 mph, 7-11 kph
Observations: Tree leaves rustle, flags wave slightly, small wavelets or scale waves
Force 3
Strength: Gentle Breeze
Speed: 8-12 mph, 12-19 kph
Observations: Leaves and twigs in constant motion, small flags extended, long un-breaking waves
Force 4
Strength: Moderate Breeze
Speed: 13-18 mph, 20-29 kph
Observations: Small branches move, flags flap, waves with some whitecaps
Force 5
Strength: Fresh Breeze
Speed: 19-24 mph, 30-39 kph
Observations: Small trees sway, flags flap and ripple, moderate waves with many whitecaps
Force 6
Strength: Strong Breeze
Speed: 25-31 mph, 40-50 kph
Observations: Large branches sway, flags beat and pop, larger waves with regular whitecaps
Force 7
Strength: Moderate Gale
Speed: 32-38 mph, 51-61 kph
Observations: Whole trees sway, large waves ("heaping sea")
Force 8
Strength: Fresh Gale
Speed: 39-46 mph, 62-74
Observations: Twigs break off trees, moderately high sea with blowing foam
Force 9
Strength: Strong Gale
Speed: 47-54 mph, 75-87 kph
Observations: Branches break off trees, shingles blown from roofs, high crested waves
Force 10
Strength: Whole Gale
Speed: 55-63 mph, 88-101 kph
Observations: Some trees blown down, damage to buildings, high churning white sea
Force 11
Strength: Storm
Speed: 64-74 mph, 101 kph-119 kph
Observations: Widespread damage to trees and buildings, mountainous waves
Force 12
Strength: Hurricane
Speed: 75 mph or greater, 120 kph or greater
Observations: Severe and extensive damage
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