Station Observations

The station still uses traditional meteorological equipment housed in a Stevenson's Screen:

  • Maximum Temperature Thermometer
  • Minimum Temperature Thermometer
  • Wet and Dry Bulb Thermometers (used to calculate the relative humidity)

In addition a grass minimum thermometer is in place on the lawn and a standard rainguage located to ensure maximum catch.

A good quality aneroid barometer and whirling hygrometer are available.

All other observations are done by eye. The range of data record each day is shown in the table below. Instrument based observations are made at 0800, 1700 and 2000 hours each day GMT/UTC.

 

Observation Method/Procedure
Maximum and Minimum Temperatures Records taken at 0800 each day and thrown back ot the previous 24 hours. All temperature are recorded to one decimal place of a degree, using the Celsius scale.

 

For the purposes of returns to the Climatological Observers Link the minimum temperature is attributed to the current day. This is the official Met Office standard, but I have never applied it for my own personal records because it can result in very misleading temperatures being listed for specific days, e.g. a very low minimum temperature, say -10oC, on one morning may coincide with the time of the morning reading; assuming the day warmed up dramatically and a warm front went through, by the following morning the temperature may have risen to 10oC; the whole of the next day may be very mild, but a minimum of -10oC will be recorded for it using the offical method!
Mean Temperature The average of the maximum and minimum for the day
Diurnal Range of Temperature The difference between the maximum and minimum for the day
Grass Minimum Temperature Recorded from the minimum thermometer at 0800 and thrown back to the previous day.
Apparent Temperature Calculated value taking into account Wind Chill (Using the recently revised NOAA formula). This states the equivalent temperature in calm conditions that would result from the same heat loss from exposed human skin.
Pressure Readings are taken 12 hours apart, at 0800 and 1200 and recorded in millibars (mb)
Dry and Wet Bulb Temperature Readings are taken from both thermometers at 0800 and 1700. The values recorded are used to calculate the percentage Relative Humidity
Precipitation Measured in millimetres (mm) at 0800 and thrown back to the previous day. Any snow, hail or ice in the rainguage is thawed out before measuring is done.
Visibility This is assessed at the time of the morning observation and record again each time there is a significant change in value. It is recorded in Beaufort Visibility Code The occurrence of fog (visibility <=3) and mist (visibility<=4) is recorded, as well as good (>=7) or excellent (=9) visibility using boolean values.
Wind Direction Recorded using the 16 compass directions, plus calm
Wind Force Recorded using the Beaufort Wind Scale
Cloud Cover Recorded at 0800 and 1700 as a percentage. In the monthly reports it is also sometimes expressed as oktas
Snow Boolean values are used to record whether snow was falling at any time during the 24 hours of the calendar day, or lying at 0900 UTC.
Hail Boolean values are used to record whether any hail fell at any time during the 24 hours of the calendar day. Further boolean values are used to record the average size of the hailstones, which are split into two categories: less than 5mm diameter (measured across the smallest axis), and 5mm or more in diameter.
Thunder Boolean values are used to record whether any thunder was heard at any time during the 24 hours of the calendar day.
Weather Details of the weather are recorded as a text string using a modified form of Beaufort Code. You can download a full explanation of the code used here. Details of cloud cover and types are also indicated. You can find a full account of the cloud codes here