One of the features of each episode is they all conclude with a reading of the weather log that describes the meteorological conditions of the night as the beautiful strains of Camille Saint-Saëns' 'The Swan' (Le Cygne) plays us out.
I talk a little bit about the background of why I wanted to include this feature in episode 49: Shipping Forecasts and Weather Logs.
The weather log always takes the following format:
Temperature outside: [Degrees Celsius]
- These are unscreened local readings taken from just outside the boat.
Temperature inside: [Degrees Celsius]
- I take this temperature from inside the main cabin. There can be quite a difference between floor level (which is effectively under water), which is cooler, and the ceiling - although fans help to ameliorate this difference. Thermometer is placed at shoulder height.
- Records the amount of water vapour in the air (Relative Humidity of RH). As well as determining dew point (see below), the moister the air, the colder it will feel in the wind (wind chill). As an island, our climate tends to be quite high in humidity. This can explain why visitors from Alaska or Scandanvia can find our (UK) winters a lot 'colder' than their own - even though they may experience much lower air temperatures. In summer, high humidity can have the opposite effect which results in making the day feel even hotter!
Dew point: [Degrees Celsius]
- Dew point is the temperature at which water vapour (measured by humidity) will turn into water. When air cools to this point cloud or fog forms. When the ground cools to dew point dew (or frost) will form.
Wind direction: [Compass points]
- Denotes direction wind is coming from according to the cardinal compass points. Wind direction can often provide clues about present or coming weather conditions. As a rule of thumb, westerlies are usually wet, easterlies dry. Prevailing winds are generally west.
Wind strength: [Miles per hour].
- For narrowboaters possibly the most significant and eagerly sought for piece of information!
Barometric pressure: [Millimetres of mercury]
- This is the measurement of air pressure. Generally the higher the pressure the more stable the weather which results in calm or less changeable weather, and the lower it is the more unstable the weather (resulting in storms and wind). However, it is the rate of change that can be more significant. Severe swings upwards or downwards presage strong winds.
Cloud cover: [Percentage]
- The amount of the sky covered by cloud.
Cloud ceiling: [Feet]
- Cloud height can tell us a lot about what is happening in the atmosphere above us. Low cloud can (although not always) indicate imminent rain, while higher cloud can indicate oncoming frontal systems which warn us to expect changes in the weather.
Chart for classifying types of clouds Chart produced by the Met Office. Source: World Meteriological Association.
- The records I can access are fairly imprecise, but show the approximate amount of rain that has fallen within the last 24 hours.
Moonphase: [Percentage and name of quarter]
- Apart from new and full moon, the moon has two main phases, waxing and waning. As the moon moves from new moon to full it is in its 'waxing' phase. Up until it is half lit (first quarter), it is waxing crescent and then it moves into its gibbous phase (therefore, 'waxing gibbous') when the moon is more than half illuminated. This is reversed as it 'wanes' moving from full moon back to new moon. I talk about this cycle in episode 57: A Rhythm of Cycles.
Main phases of the moon. Image source: Griffith Observatory.
Day length: [Hours and minutes]
- This is taken from sunrise to sunset.
Sunset: [Hours and minutes]
- Episode 35: Twilight Blue explored the three different twilight (civil, nautical, and astronomical). This reading relates to the time the sun dips below the horizon.
Sky casting: [Hours and minutes]
- 'Sky casting' is a term I came across in Weather folk-Lore of the Sea and Superstitions of the Scottish Fishermen (c. 1900) and it is the old name used by fishermen on the east coast of Scotland. It is a fairly imprecise term and actually includes any time from the lightening of the sky to the rising of the sun and just afterwards. However, I love it and decided to use it - the times given refer to astronomical sunrise.