Author Topic: Beaufort Weather Code Charts  (Read 22760 times)


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Beaufort Weather Code Charts
« on: October 17, 2010, 07:02:47 am »

This is a list of weather codes (used worldwide until computers had the system changing over to numbers) developed for the Royal Navy in the early part of the 19th century.  This list has been borrowed from another link. It has the original text in its entirety, with some additions to include codes found in our ship logs.  PLEASE NOTE: You don't need to know all of these in order to do an excellent job on the log sheets.  It's a good reference spot when you need to see if those squiggly lines really say "bc" and if that makes sense.  There's a lot of info here you won't need at all, but I'm leaving it intact because it's interesting. 

It helps to know that an "okta" in the RN logs is 1/8th of the sky; US logs use tenths of the sky. 

Have at it!



Beaufort Code is a system which uses letters and numbers to denote various weather types.  The tables below provide full details of Beaufort Code. At the end of this document is a section describing how to write and interpret Beaufort Code.



b - Clear blue sky Cloud cover: 0 to 2 oktas (0 - 25%) or 0 to 3 tenths (0 - 30%)

bc - Partly cloudy Cloud cover: 3 to 5 oktas[/b] (26 - 74%) or 4 to 6 tenths (40 - 60%)

c - Cloudy Cloud cover: 6 to 8 oktas (75 - 100%) or 7 to 9 tenths (70 - 90%) (Blue sky behind the clouds)

o - Uniform layer of cloud completely covering the sky (100%)

oc - Overcast sky with detached clouds below

g - Gloomy, or dark stormy-looking sky

u - Ugly, threatening Sky (e.g. before the onset of a thunderstorm)


r - Rain (drops of water >0.5mm diameter)

rx - Freezing Rain (i.e. rain which freezes on contact with the ground and vegetation)

d - Drizzle (drops of water <0.5mm diameter)

dx - Freezing Drizzle (i.e. drizzle which freezes on contact with the ground and vegetation)

s - Snow (ice crystals, often branched into 'flakes' in 'warmer conditions', temperatures >-5oC

h - Snow Pellets (often referred to as 'soft hail', and typical of wintry showers, especially in coastal regions; white and spherical or conical, 2 to 5mm; fall only from cumulus and cumulonimbus clouds )

h - Hail (transparent or opaque particles , usually spheroidal, but sometimes conical; over 5mm; can fall as larger aggregated lumps in heavy thunderstorms; most larger hailstones show evidence of concentric layering)

Small Hail (as above but consisting of snow pellets encased in a thin layer of clear ice, not easily crushable; under 5mm; very common in showery weather in Britain; falls only from cumulus and cumulonimbus clouds) Ice Pellets (spherical, conical or irregular transparent ice particles <=5mm; fall mainly from altostratus and nimbostratus clouds)

Diamond Dust (tiny ice crystals which fall from a clear sky; requires very cold weather; rare in Britain; common in polar regions)

sh - Snow Grains (white opaque particles <1mm; fall usually from low stratus and stratocumulus clouds)


f - Fog (Visibility <1km)

Royal Navy fog scale:
f1 - Light fog or mist - Horizon invisible, but lights and landmarks generally visible at working distances.  Objects indistinct but navigation unimpeded.
f2 & f3 - Moderate fog - Lights, passing vessels, and landmarks generally indistinct at working distances.  Fog signals sounded.  Navigation impeded, additional caution required.
f4 & f5 - Thick fog - Ships' lights and vessels invisible 1/4 miles or less.  Navigation suspended.

fx - Freezing Fog (water droplet fog, that freezes on contact with solid objects)

fe - Wet Fog (damp fog which deposits a film of water on exposed solid surfaces)

fs - Shallow Fog Patches (fog limited to a depth of 2 metres or less; if it is a continuous layer, the lower line of the symbol is continuous, but the Beaufort code stays the same)

m - Mist (Visibility 1 to 2 km; there are a variety of definitions of mist; the British Met Office also require a relative humidity between 95 and 100%)

ks - Drifting Snow (snow raised to heights below eye level - 1.8 metres; no overall reduction in visibility)

ks - Blowing Snow (snow raised to a great height above the land surface causing severe reduction of visibility, e.g. a 'white-out'; strong winds needed; usually limited to upland areas in Britain, common in North American's midwest and plains.)

w - Dew (produced by night-time radiation cooling)

w - Advection Dew (caused by condensation on upright surfaces, usually after a cold spell as warm moist air blows against cold surfaces)

w - White Dew (frozen dew drops, as opposed to hoar frost)

x - Hoar Frost (the 'usual' white frost, produced by radiation cooling; takes the form of small needles, scales, feathers or fans)

x - Advection Hoar Frost (forms in the same way as advection dew, but with temperatures still below freezing)

dr - Drizzle and rain

rs - Rain and snow (Sleet)

hs - Hail and snow

hr - Hail and rain


z - Haze (the presence of microscopic particles in the air in sufficient quantities to give the sky an opalescent appearance; visibility is often reduced; most common in calm anticyclonic weather in summer in Britain, when pollen, dust and pollution contaminate the air)

t - Thunder

tl - Thunderstorm (thunder must be audible at the site before a thunderstorm can be recorded)

l - Lightning (there are three common types: ground discharge - where the lightning strikes the ground; it is often in a ranched form, hence the name 'forked' lightning; cloud discharge - lightning that is within the cloud - its channel is often ndistinguishable and we normally refer to it as 'sheet' lightning; air discharge - often sub-horizontal, it runs from cloud to air outside the cloud; sometimes called 'streak' lightning; a fourth an rare form is ball lightning, which appears near the ground usually after a ground discharge; it varies between 10cms and 1 metre in diameter, 'floats' around for several seconds and usually dissipates with a violent explosion)

j - Within Sight (used as a suffix for other phenomena, e.g. pj = shower within sight, but not over the recording station.

e - Wet Air (wet air, but without rain falling)

y - Dry Air (relative humidity < 60%)

v - Abnormally good visibility (e.g. over 50 miles) in RN logs; may also be
v - Variable weather in US logs

p - Passing shower (a relatively short period of precipitation; the type is indicated by additional letters or symbols)

g - Gale (wind speed averaging between 34 and 47 knots for a period of 10 minutes or more)

G - Storm (wind speed averaging over 47 knots for a period of 10 minutes or more)

q - Squall (a strong wind that rises suddenly and lasts for at least a minute then dies away relatively quickly; an increase of 16 knots to a speed over 22 knots is required)

kq - Line Squall (as above but occurring along the line of a cold front and accompanied by a roll shaped cloud with a horizontal axis and a sharp fall in temperature)



We need to differentiate between, light/weak, moderate, heavy and violent/Severe events, such as rainfall, thunderstorms, lightning, (and to a lesser extent with fog), fog, etc.

Weak/Light: a subscripted suffixed 'o' is used, e.g. ro, so, do mean light rain, snow and drizzle respectively. For very light precipitation a double 'o' may be used, e.g. soo  This, however, is non-standard.

Moderate: simple lower case letters, e.g. r, s, d, f, tl

Heavy: capital letters, e.g. R, S, D, H, F,TL

Violent/Severe: a subscripted suffixed '2' is used, following a capital letter e.g. R2 indicates torrential rain.

The same procedure is used for rain, hail, etc.


If a phenomenon is continuous, the code is simply repeated, e.g. rr represents continuous rain, soso represents continuous light snow.  If a phenomena is intermittent (i.e. broken by intervals less than an hour long) the prefix 'i' is used, e.g. iro means intermittent light rain.


The difference between a lengthy shower and a period is rather subtle.  By definition showers can only fall from convective cloud (cumulus and cumulonimbus), and are usually broken by sunny spells or clear interludes.  There is no standard way of differentiating between short, medium and lengthy showers.  However, an easily applied non-standard solution is to use the same suffixes as for intensity, to refer to length, e.g.

poR = short shower of heavy rain.

pooroo = fleeting shower of very light rain, e.g. just a few drops, not enough to completely wet the ground.

Pro = lengthy short of light rain.


This is another non-standard convention.  Official staffed weather stations would actually record the precise times of showers.  For those of us who have other jobs to do the following method may suffice:

(f)poRH = frequent short showers of heavy rain and hail

(o)pro = occasional showers of light rain

Ensure that the brackets are used, otherwise 'f' means 'fog' and 'o' means 'overcast'.


When several phenomena occur together they are recorded in the following order:

State of sky
Atmospheric obscurity (visibility)
Other phenomena

Example: cTLrzu = cloudy with a heavy thunderstorm and moderate rain, haze present and an ugly threatening sky.


Beaufort Code can be used for a current weather status report, i.e. for a fixed point in time, or it can be used to record weather throughout the day, to show the sequence of weather events.  Where it is used to represent a sequence a comma can be used to separate events, e.g.

Code: b, bc, c, oiro, ororo, orr, cRR, bc(o)pR

Translation: cloud cover less than 2 oktas increasing to over 6 oktas, eventually 8 oktas with a dull featureless sky and intermittent light rain, becoming continuous, moderate and heavy, with a more differentiated cloudy sky of 8 oktas, followed by a cloud cover of 3 to 5 oktas and occasional showers of heavy rain.

Most observers will add additional information in code sequences, often in brackets, e.g. the time of certain events, descriptions of phenomena which have no eaufort Code (the international symbols may be used), number of discharges in a thunderstorm, types of cloud present, etc. Curly brackets are used to indicate sunrise } and sunset {, e.g. RR } c = continuous heavy rain before sunrise, followed by cloudy dry weather after sunrise

Cloud cover and types of cloud are also embedded in the Beaufort Code strings, inside square brackets, e.g. [50Cu(con)], which would indicate a cover of 50% Cumulus congestus.

There is a separate download available covering cloud codes.


The details of thunderstorms are included inside a double set of backslashes, e.g.
\\[0130-0215][33cc25cg]\\ which means the storm lasted from 0130 to 0215 GMT/UTC and consisted of 33 inter-cloud discharges (usually appearing as sheet lightning, especially at night) and 25 cloud to ground (or vice-versa) discharges.


Snow lying (over 50% ground cover) at any point in the day is indicated by the usual Beaufort letters, plus a double superscripted asterisk, e.g.

The average snow depth is indicated inside square brackets using centimetres or millimetres


Fronts are indicated by a double set of capital letters:

WF - warm front

CF - cold front

OF - occluded front

SF - stationary front

which are colour coded with the F subscripted in downloaded excel spreadsheets, but not in queries running from the website, which simply return two capital letters.
« Last Edit: September 15, 2016, 10:27:39 pm by DJ_59 »

Janet Jaguar

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Re: Weather Code Charts
« Reply #1 on: October 14, 2012, 06:14:41 pm »
The ships' logbooks (original books that stayed with the ship, not necessarily the monthly copies sent home) all had a shortened list of possible weather codes to be used by the log keepers, as well as a clearly definition of wind force.  US logbooks had a list of cloud symbols, and RN logbooks had definitions of fog intensity.  Those printed charts are shown below.  It is noted that some log keepers knew and used the expanded list given above.

Various US log instructions can be read in whole at these links.  I have also embedded some of the specifics below.

US Navy 1879
US Coast and Geodetic Survey Ship Logs 1922:,%201922/IMG_7868_0.jpg,%201922/IMG_7868_1.jpg,%201922/IMG_7869_0.jpg,%201922/IMG_7869_1.jpg
US Coast Guard 1942
US Navy 1947

US Navy Logbook c.1900:

See the full 3 pages of instructions in various US logbooks. 

US Navy Logbook c.1947:

See the full 3 pages of instructions in various US logbooks. 

Cloud symbols occupy almost a full column.  See them on the instruction page.

Royal Navy Logbook 1913:

See the original full page of Instructions in the RN logbooks.
« Last Edit: September 28, 2013, 03:12:19 pm by Janet Jaguar »

Janet Jaguar

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Re: Weather Code Charts
« Reply #2 on: December 31, 2012, 11:15:13 pm »
We did not include State of the Sea in our weather readings in Classic OW, because sea swells can be generated by storms a thousand miles away and only confuse the local weather.  But we are using them now in the New Old Weather and in Old Weather: Whaling, and a number of us like to know when the sea is being unusually rough.  Wonderful pictures of the state of the sea are shown in this document from the Met Office beginning at page 11.

These are the codes used to describe the State of the Sea in our log books:

US Navy Logs c. 1900

This chart from the US Navy instructions gives the State of the Sea, and also explains some of the misc. symbols we have seen in the logs from both navies.

US Navy Logs c. 1947

RN Logs c. 1915

A Modern Chart can be found at Sea Disturbance; it is much more detailed than what is in either of our navies instructions.

« Last Edit: December 28, 2015, 06:34:38 pm by Janet Jaguar »

Janet Jaguar

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Re: Weather Code Charts
« Reply #3 on: June 02, 2013, 12:43:28 pm »
We have found an article laying out the foundations of the Beaufort weather code system, going back to 1685.  Log keepers tended to standardize words so as to be understandable by anyone who was themselves a mariner.
British Naval Logbooks from the Late Seventeenth Century: New climatic information from old sources

« Last Edit: September 16, 2016, 04:59:29 pm by Caro »

Janet Jaguar

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Re: Weather Code Charts
« Reply #4 on: June 02, 2013, 11:33:47 pm »
And then there is this 1906 illustration of wind strength. ;D

« Last Edit: October 05, 2015, 08:41:10 pm by Janet Jaguar »