|
Weather Terms |
|
Some of the less common weather
parameters calculated by my weather stations are
described here.
Further information can be found by
following the
Wikipedia hyperlinks.
Davis Instruments description of how they are
calculated.
 |
|
Apparent Temperatures |
|
Parameter |
Description |
|
Heat Index |
Uses temperature and relative humidity to
determine how hot the air "feels". |
| THSW Index |
Uses Temperature and relative Humidity
along with Sun and Wind to determine what
it "feels" like in the sun. |
|
Wind Chill |
Takes into account how the wind speed
affects our perception of the air temperature. |
|
| Average Wind Direction |
The Vantage Pro2 calculates a 10-minute
average wind direction. |
| Average Wind Speed |
The Vantage Pro2 calculates a 10-minute
wind speed |
|
Cooling Degree Day |
Quantitative index designed to reflect
the demand for energy needed to cool a home. |
| Daily Rain |
Displays the rain accumulated since 12
mid-night. |
|
Degree
Day |
Description of Degree Days from
BizEE Software |
|
Dew
Point |
Temperature to which air must be cooled
for saturation (100% RH) to occur, providing there is no
change in water vapour concentration. |
|
EvapoTranspiration (ET) |
Combination of the words "evaporation"
and "transpiration".
Provides a measure of the amount of water vapour
returned to the air in a given area. Effectively, ET is
the opposite of rainfall and is expressed in the same
units (in, mm) and is calculated by
measuring Solar Radiation, Wind Speed, Temperature and
Humidity. |
|
Heating Degree Day |
Quantitative index designed to reflect
the demand for energy needed to heat a home. |
|
Solar Radiation |
Displays the current solar radiation in
W/m2. |
|
Solar Energy |
The amount of accumulated solar
radiation energy over a period of time is measured in
Langleys.
1 Langley = 11.622
Watt-hours per square meter
= 3.687 BTUs per square foot
= 41.84 kilojoules per square meter |
| Storm Rain |
Displays the rain total of the last rain
event. The Davis Weather Instrument takes two tips of
the rain bucket (02") to begin a storm event and 24
hours without rain to end a storm event. |
|
UV (Ultra Violet) Radiation |
Exposure to UV rays can cause a range of
health problems, such as sunburn, skin cancer, skin
aging etc. The Vantage Pro2 displays UV readings in two
scales: MEDs and UV Index. |
| UV MEDs |
MED (Minimum Erythemal Dose) is defined
as the amount of sunlight exposure necessary to induce a
barely perceptible redness of the skin within 24 hours
after sun exposure. Because different skin types burn at
different rates, 1 MED for persons with dark skin is
different from 1 MED for persons with very light skin.
|
Skin Type |
Skin Colour |
Tanning & Sunburn History |
| 1 - Never tans,
always burns |
Pale or milky
white; alabaster |
Develops red sunburn; painful
swelling, skin peels |
| 2 - Sometimes
tans, usually burns |
Very light brown;
sometimes freckles |
Usually burns, pinkish or red
colouring appears; can gradually develop light
brown tan |
| 3 - Usually tans,
sometimes burns |
Light tan; brown
or olive; distinctly pigmented |
Rarely burns; shows
moderately rapid tanning response |
| 4 - Always tans,
rarely burns |
Brown, dark
brown, or black |
Rarely burns, shows very
rapid tanning response |
|
|
UV Index |
UV Index assigns a number between 0 and
16 to the current UV intensity. The lower the number,
the lower the danger of sunburn.
|
Index Values |
Exposure Category |
| 0 - 2 |
Low |
| 3 - 4 |
Moderate |
| 5 - 6 |
High |
| 7 - 9 |
Very High |
| 10+ |
Extreme |
|
|
Wind Run |
Wind run is measurement of the "amount"
of wind passing the station during a given period of
time, expressed in either "miles of wind" or "kilometers
of wind". WeatherLink calculates wind run by multiplying
the average wind speed for each archive record by the
archive interval. For Example:
Average Wind Speed = 5 mph
Archive Interval = 30 minutes
(0.5 hours)
Wind run = 5 mph x 0.5
hours = 2.5 miles of wind |
