MetLink Recording Hints
- General hints and use of MetLink weather database
- Cloud cover
- Pressure
- Rainfall
- Relative Humidity
- Temperature
- Weather description & SYNOP code
- Wind direction
- Wind speed (Beaufort Scale)
Please check your barometer. You should be able to find a station near you by going to:
http://weather.noaa.gov/weather/ccworld.html or http://www.wunderground.com/
What is a barometer?
Barometers are instruments used to measure atmospheric pressure. (Barographs are instruments which provide a record of the pressure, often on a paper chart.)
What units are pressure measured in?
Pressure is measured in Pascals in the metric system, but barometers are often calibrated in inches of mercury or millibars (1 millibar = 1 hectoPascal = 100 Pascals). Divide the reading in inches of mercury by 0.0295 to convert it to a pressure in millibars. Some continental barometers are calibrated in centimetres of mercury. To convert this to a reading in millibars, first multiply the number of cm by 2.54 to get to inches of mercury, and then divide by 0.0295 as above. More information on units.
Why do you need to set your barometer?
Atmospheric pressure varies with height above sea level as well as with atmospheric conditions. As the height at which a barometer operates is usually constant, a correction is made to make the reading of a barometer seem as if it were made at sea level. This means that the pressure reading has to be slightly increased from the value it has read on a barometer above sea level.
Pressure maps shown on the television and in newspapers show pressures which are corrected to the values which would be measured at sea level. If a barometer's pressure reading is to be compared with pressure maps distributed by the Media, then it first needs to be set to read sea level pressure.
How can you set your barometer?
The easiest way to set a barometer is to adjust it to give the same reading as that on a weather chart for your area at the same time. This is best done in atmospheric conditions when the pressure varying only very slowly. Anticyclones are ideal for this, often associated with established clear and sunny (but sometimes foggy in winter) conditions. Don't adjust it when conditions are unsettled or windy.
You can only make the adjustment to the barometer if you have an aneroid barometer, usually by a small screw on the back of the barometer, but the instructions will need to be consulted. Mercury barometers (these contain mecury and are about a metre long) should not be tampered with as a mecury spillage presents a safety hazard.
After you have made the adjustment, the barometer should give a reading of pressure which is the same as that on a weather chart for the same time. Note that you need to use a chart of the analysis (i.e. what the values actually were), rather than a forecast.
Where can you get standard pressure readings from?
Two standard barometers which can be consulted using the web are, amongst other places, at:
Department of Meteorology at Reading and as a graph of station (not sea level) pressure National Physical Laboratory online barograph at Teddington
They both read station pressure and sea level pressure, but you need to be close to them for these readings, if they are steady, to be at all useful.
SYNOP Code
The SYNOP code (shown below) has about 100 descriptions of the current weather.
For more information see: http://www.brixworth.demon.co.uk/weather19.htm
00 -- clear skies 01 -- clouds dissolving 02 -- state of sky unchanged 03 -- clouds developing Haze, smoke, dust or sand 04 -- visibility reduced by smoke 05 -- haze 06 -- widespread dust in suspension not raised by wind 07 -- dust or sand raised by wind 08 -- well developed dust or sand whirls 09 -- dust or sand storm within sight but not at station Non-precipitation events 10 -- mist 11 -- patches of shallow fog 12 -- continuous shallow fog 13 -- lightning visible, no thunder heard 14 -- precipitation within sight but not hitting ground 15 -- distant precipitation but not falling at station 16 -- nearby precipitation but not falling at station 17 -- thunderstorm but no precipitation falling at station 18 -- squalls within sight but no precipitation falling at station 19 -- funnel clouds within sight Precipitation within past hour but not at observation time 20 -- drizzle 21 -- rain 22 -- snow 23 -- rain and snow 24 -- freezing rain 25 -- rain showers 26 -- snow showers 27 -- hail showers 28 -- fog 29 -- thunderstorms Duststorm, sandstorm, drifting or blowing snow 30 -- slight to moderate duststorm, decreasing in intensity 31 -- slight to moderate duststorm, no change 32 -- slight to moderate duststorm, increasing in intensity 33 -- severe duststorm, decreasing in intensity 34 -- severe duststorm, no change 35 -- severe duststorm, increasing in intensity 36 -- slight to moderate drifting snow, below eye level 37 -- heavy drifting snow, below eye level 38 -- slight to moderate drifting snow, above eye level 39 -- heavy drifting snow, above eye level Fog or ice fog 40 -- Fog at a distance 41 -- patches of fog 42 -- fog, sky visible, thinning 43 -- fog, sky not visible, thinning 44 -- fog, sky visible, no change 45 -- fog, sky not visible, no change 46 -- fog, sky visible, becoming thicker 47 -- fog, sky not visible, becoming thicker 48 -- fog, depositing rime, sky visible 49 -- fog, depositing rime, sky not visible Drizzle 50 -- intermittent light drizzle 51 -- continuous light drizzle 52 -- intermittent moderate drizzle 53 -- continuous moderate drizzle 54 -- intermittent heavy drizzle 55 -- continuous heavy drizzle 56 -- light freezing drizzle 57 -- moderate to heavy freezing drizzle 58 -- light drizzle and rain 59 -- moderate to heavy drizzle and rain Rain 60 -- intermittent light rain 61 -- continuous light rain 62 -- intermittent moderate rain 63 -- continuous moderate rain 64 -- intermittent heavy rain 65 -- continuous heavy rain 66 -- light freezing rain 67 -- moderate to heavy freezing rain 68 -- light rain and snow 69 -- moderate to heavy rain and snow Snow 70 -- intermittent light snow 71 -- continuous light snow 72 -- intermittent moderate snow 73 -- continuous moderate snow 74 -- intermittent heavy snow 75 -- continuous heavy snow 76 -- diamond dust 77 -- snow grains 78 -- snow crystals 79 -- ice pellets Showers 80 -- light rain showers 81 -- moderate to heavy rain showers 82 -- violent rain showers 83 -- light rain and snow showers 84 -- moderate to heavy rain and snow showers 85 -- light snow showers 86 -- moderate to heavy snow showers 87 -- light snow/ice pellet showers 88 -- moderate to heavy snow/ice pellet showers 89 -- light hail showers 90 -- moderate to heavy hail showers Thunderstorms 91 -- thunderstorm in past hour, currently only light rain 92 -- thunderstorm in past hour, currently only moderate to heavy rain 93 -- thunderstorm in past hour, currently only light snow or rain/snow mix 94 -- thunderstorm in past hour, currently only moderate to heavy snow or rain/snow mix 95 -- light to moderate thunderstorm 96 -- light to moderate thunderstorm with hail 97 -- heavy thunderstorm 98 -- heavy thunderstorm with duststorm 99 -- heavy thunderstorm with hail
Hints on making your own anemometer
http://www.geocities.com/~worsleyschool/science/anemometer.html
Beaufort Wind Scale (from Force 0 to 12)
|
Scale |
Wind Name |
Speed kph |
Decription |
|
0 |
Calm |
0 |
smoke rises vertically |
|
1 |
Light air |
1-5 |
direction shown by smoke but not by wind vanes |
|
2 |
Light breeze |
6-11 |
wind felt on face, leaves rustle, wind vane moved by wind |
|
3 |
Gentle breeze |
12-19 |
leaves and small twigs in constant motion; light flags extended |
|
4 |
Moderate breeze |
20-28 |
raises dust and loose paper, small branches are moved |
|
5 |
Fresh breeze |
29-38 |
small trees in leaf begin to sway; crests on inland water |
|
6 |
Strong breeze |
38-49 |
large branches in motion; umbrellas used with difficulty, whistling in telegraph wires |
|
7 |
Moderate gale |
50-61 |
whole trees in motion; inconvenience felt when walking against wind |
|
8 |
Fresh gale |
62-74 |
twigs break off trees; generally impedes progress |
|
9 |
Strong gale |
75-88 |
slight structural damage, chimney-pots and slates removed |
|
10 |
Whole gale |
89-102 |
trees uprooted, considerable structural damage |
|
11 |
Storm |
103-117 |
widespread damage, very rarely experienced |
|
12 |
Hurricane |
118 plus |
devastation |