KLB School Weather Station - Help / Glossary

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KLB School Weather Site: Help / Glossary

Index of weather station terms:

Heat Index - this apparent temperature is calculated using the actual temperature and the relative humidity. It therefore takes into account the fact that when humidity is low, the air temperature will feel lower than it actually is, since perspiration evaporates more rapidly to cool the body. When humidity is high the reverse is felt since perspiration evaporates more slowly.
THW Index - this apparent temperature is calculated using the actual temperature, the relative humidity and the wind speed. It therefore takes into account the cooling and heating effects of wind and the effect of humidity on our perception of temperature. It is in effect a combination of the wind chill temperature and the heat index temperature.
Wind Chill - this apparent temperature is calculated using the actual temperature and the wind speed. If there is no air movement then the layer of air next to the skin insulates us to some extent and the air temperature will feel warmer than it actually is. As the wind speed rises, this layer is more rapidly blown away and the air temperature will feel colder than it actually is.
Humidity - this means relative humidity. Relative humidity takes into account the temperature and air pressure (because both these alter the amount of moisture the air is capable of holding). Relative humidity is therefore not actually a measure of the amount of water vapour in the air, but a percentage of the air’s water vapour content compared to the amount the air is actually capable of holding.
Dew-Point - this is the calculated temperature to which air must be cooled for saturation (100% relative humidity) to occur. As air cools, it loses its ability to hold water and if it cools below the dew-point then the water vapour in the air has to condense (change into a liquid) to form dew, clouds, fog or frost of it is cold enough. If the dew-point and the temperature are close together in the late afternoon, when the air begins to turn colder, fog is likely during the night.
Cloud Base - this is the calculated estimate of the height of the base of any clouds that might be present. The calculation uses the dew-point and the actual temperature and the formula is based on the fact that as a mass of air rises, particularly on warm and humid days, it expands in the lowering air pressure, causing the air mass to cool and greatly reducing the air's ability to hold moisture. When the rising air has cooled to the point where the moisture in the air exceeds the value which that air mass can hold, the water vapour condenses to form clouds.

Information on Infrared satellite images:

Infrared (IR) radiation is the invisible 'heat' radiation that is given off by all warm objects, the greater the temperature the more intense the radiation.
Special IR sensors in a satellite detect the intensity of this radiation 24 hours a day as is given off by the tops of clouds, the land surface and the ocean surface.
The level of intensity detected is converted into a greyscale image, with cooler temperatures showing as lighter greys and warmer temperatures as darker greys.
High clouds, being cold, show up clearly and this means weather features like fronts and shower clouds are easy to make out with IR satellite images. However, low cloud, which has a similar temperatures to the underlying surface, is less easy to distinguish.
The images are updated every 6 hours from 00:00 UTC and usually take about 20 minutes to be processed and have the coast-line and the lines of latitude / longitude added for clarity.
The time shown on the image is in UTC (Coordinated Universal Time) which is basically the same as GMT (Greenwich Mean Time).

Information on EUMETSAT's satellite images:

Images of the globe are taken routinely by EUMETSAT's Meteosat satellites from the geostationary orbit about 36000 km above the equator. The images are taken on a half-hourly basis and upladed to the Internet after processing.

The Beaufort scale

The Beaufort scale is used to estimate wind strengths from observations of its effects. The scale starts with 0 and goes to a force of 12.

WIND FORCE	EQUIVALENT SPEED (miles per hour)	DESCRIPTION	OBSERVATIONS
0	0 - 1	Calm	Smoke rises vertically.
1	1 - 3	Light air	Direction of wind shown by smoke drift, but not by wind vanes.
2	4 - 7	Light Breeze	Wind felt on face; leaves rustle; ordinary vanes moved by wind.
3	8 - 12	Gentle Breeze	Leaves and small twigs in constant motion; wind extends light flag.
4	13 - 18	Moderate Breeze	Raises dust and loose paper; small branches are moved.
5	19 - 24	Fresh Breeze	Small trees in leaf begin to sway; crested wavelets form on inland waters.
6	25 - 31	Strong Breeze	Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
7	32 - 38	Near Gale	Whole trees in motion; inconvenience felt when walking against the wind.
8	39 - 46	Gale	Breaks twigs off trees; generally impedes progress.
9	47 - 54	Severe Gale	Slight structural damage occurs (chimney-pots and slates removed).
10	55 - 63	Storm	Seldom experienced inland; trees uprooted; considerable structural damage occurs.
11	64 - 72	Violent Storm	Very rarely experienced; accompanied by wide-spread damage.
12	73 - 83	Hurricane	!!!

Help downloading Text Files of archive data and opening them in MS Excell

2 Day and 1 Week archived data. (Note: the layout of the data in these text files means they are relatively easy to open in the correct columns in MS Excel)
Reports for the current and previous month/year. (Note: the layout of the data in these text files makes opening them in the correct MS Excel columns a bit more complicated)