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For the purposes of the meteorological logbook, the term 'weather' embraces those elements covered by the 'present weather' and 'past weather' codes, i.e. fog, precipitation, etc. (see Met.O.509, Ships' Code and Decode Book).

For a concise description of weather, Admiral Beaufort devised a system known as the Beaufort notation. Since 1958 this method has not been used to record weather at the synoptic hour but it is given below as it provides a handy way of amplifying the main synoptic report, or of recording the weather between observations, e.g. duration of precipitation, in the remarks column of the meteorological logbook for research purposes. It may also be found useful in the Deck Logbook and in the plotting of weather bulletins.

The present codes are sufficient to describe the weather for synoptic purposes, and they are also suitable for data processing by computer or by other machine methods.

The Beaufort notation

Weather Beaufort Weather Beaufort letter letter

Blue sky (0-2/8 clouded) | b | Overcast sky (unbroken cloud covering sky) | o

Sky partly clouded (3-5/8) |  | bc | Squally weather | q
Cloudy (6-8/8 clouded) |  | c | Rain | r
Drizzle |  | d | Sleet (rain and snow together) | rs

Wet air (without precipitation) | e | Snow | s
Fog | f | Thunder | t
Gale | g | Thunderstorm with rain | tlr
Hail | h | Thunderstorm with snow | tls
Precipitation in sight of ship or station | jp | Ugly threatening sky | u
Line squall | kq | Unusual visibility | v
Storm of drifting snow | ks | Dew | w
Sandstorm or duststorm | kz | Hoar-frost | x
Lightning | 1 | Dry air | y
Mist | m | Dust haze | z

The system has been extended since Beaufort's day to provide indication of intensity and continuity. Capital letters are now used to indicate occasions when the phenomenon noted is intense. On the other hand, occasions of slight intensity are distinguished by adding a small suffix 'o'.

T hus R = Heavy rain
r = Moderate rain
ro = Slight rain
The prefix 'i' indicates 'intermittent', thus:
if = Fog patches.
ir o = Intermittent slight rain.

The prefix 'p' indicates 'shower of', thus:

pR = Shower of heavy rain.

pso = Shower of slight snow.

A solidus 'l' is used in 'present weather' to distinguish present conditions from those in the past hour, thus:

c/r o = Cloudy after slight rain in the past hour.

Continuity is indicated by repeating the letter, thus:

rr = Continuous moderate rain.

The following are further examples of the use of Beaufort notation:

cs o s o = Cloudy with continuous slight snow.

oid o = Overcast with intermittent slight drizzle.

bif = Blue sky with fog patches.
cqprh = Cloudy with squalls and shower of moderate rain and hail.

crrm = Cloudy with continuous moderate rain, and mist.

In past weather the letters are used in the same way but their order from left to right indicates sequence in time. Thus 'b, bc, cpr' indicates cloudless conditions, becoming partly cloudy, followed by cloudy conditions with shower(s) of rain.