Notes on registers

As in all human recordings, there are occasional mistakes on these registers. For instance, it's possible to pick the wrong mark on the thermometer and be out by five degrees. Some mistakes have been altered with tippex (near the time), but others will remain. Roger Brugge has already been through much of the data and comments taken from his notes can be found on the webpages of the pertinent dates. (Please ask for these if you need them.)

In addition to this, there have been some other significant developments, which are listed below

Movement of the site
Change of units
Some measurements refer to earlier times
Calculations become measurements
Cloud cover
Present weather (WW)
Rainfall
Snow
State of ground
Visibility
Wind direction
Wind speed

Movement of the site

The current site on the University's Whiteknights campus was established in 1970; prior to then observations were made closer to the town centre adjacent to the London Road.

In 1892, University College, Reading was formed, and so the London Road observation site was also known as University College. The University College received its Royal Charter in 1926, so becoming the University of Reading.

The move to Whiteknight's occurred from 1 January 1968, witth a minor re-location with effect from 1 January 1970 to the present location.

The London Road site was typically 0.4 degC warmer during the day and 0.6 degC warmer at night with about 12 fewer days of air frost and 32 fewer days of ground frost over the year. Rainfall amounts were very similar at the two sites although sunshine duration amounted to about 90 hours less over the year at London Road - which was closer to the (industrial) town centre and in a less rural location. Soil temperatures at London Road were about 0.8 degC higher at a depth of 30 cm when compared to Whiteknights.

Change of units

The units of measurement have changed with time, mostly becoming increasingly metric, as shown in the table below:

Date of change Measurement(s) Old unit New unit

January 1959 cloud cover tenths eights or oktas

May 1960 wind speed knots mph

January 1971 rainfall inches millimetres

January 1971 fresh and total snow depth inches centimetres

March 1972 depth of soil temperatures inches and feet centimetres

January 1977 temperatures degrees Fahrenheit degrees Celsius

Date of change	Measurement(s)	Old unit	New unit
January 1959	cloud cover	tenths	eights or oktas
May 1960	wind speed	knots	mph
January 1971	rainfall	inches	millimetres
January 1971	fresh and total snow depth	inches	centimetres
March 1972	depth of soil temperatures	inches and feet	centimetres
January 1977	temperatures	degrees Fahrenheit	degrees Celsius

Some measurements refer to earlier times

Most of the measurements are instantaneous and so it's clear they refer to 0900 GMT or (occasionally) additional observation times. However, a measurement such as maximum temperature covers a range of times. For all maximum and minimum temperatures, rainfall, rainfall duration and wind run, the measurement should have been reset at 0900 GMT. Hence the measurements refers to the proceeding 24 hours, so starting from 0900 GMT of the preceding day and finishing - when the measurements are taken - at 0900 GMT of current day. For example, the highest temperatures usually occur in the afternoon, and so the maximum temperature will usually refer to the maximum temperature from the previous afternoon.

There are exceptions. For recording a day of snow or sleet falling, thunder or hail, the day refers to 0000 GMT to 2400 GMT of that day. However, some registers have the heading `weather since past observations', and this may refer to the previous day.

For maximum wind gust, early measurements would have been from 0000 GMT until 2400 GMT, while later measurements were from 0900 GMT of proceeding day until 0900 GMT. But it is not know when this change was made.

Calculations become measurement

Equipment has has not always been available to measure various atmospheric variables. The following readings shown in the registers were calculated by the observer from other atmospheric variables:

dew point temperature between January 1960 and February 1972
relative humidity between January 1960 and February 1972
vapour pressure between January 1960 and September 1978

Atmospheric pressure

Before November 1959, the atmospheric pressure reading, using a mercury barometer, is given in inches. When the `whole inches' part of the reading, e.g. `28.', does not change between successive days, then only the decimal part of the reading is sometimes shown on subsequent days. The pressure reading is not the mean sea level pressure, but the station level pressure - unless it is shown otherwise.

Cloud cover

From the start of 1959, cloud cover was measured by noting how many eighths of the sky are covered by the cloud, and the unit for this is oktas. Hence a recording in the register of 0 indicates no cloud while 8 indicates complete cloud cover. A recording of 9 indicates that the sky was not visible, such as in the case of fog. Sometimes cloud cover in the register was recorded as `tr' for trace, which is equivalent to 1 okta.

Before 1959, the cloud amount was measure in tenths; here `-' usually denotes no cloud but is also used to indicate the presence of fog (possibly the sky being obscured).

Between December 1910 and October 1959 under the `Cloud form' heading, the following abbreviations (which differ to the ones used today) were used:

Ni : nimbostratus
StCu : stratoscumulus
CiSt : cirrostratus

Fog is often denoted by the symbol

, the SYNOP plotting symbol for fog, while `b' often denotes a cloudles sky. The compass direction under the `Whence coming' heading indicates where cloud is approaching from in the days when the movement of cloud was observed.

Present weather (WW)

From December 1910 until October 1921 there is some notation that differs to the current Beaufort notation, so that `dr' denotes drizzle, `h' denotes haze and `*' denotes snow on occasions. In addition, the use of upper case letters does not necessarily mean intense phenomena.

From November 1921 the weather since last observation is split into two columns: weather since midnight or previous observation and weather from last observation. However it is not always clear that the information in each columns only applies to their time period.

From November 1959 a weather diary and remarks column is introduced, which provides a description of the weather during the calender day. Also from this time, the SYNOP codes for present weather are used - if more than one code applies then the highest should have been selected:

Code Meaning Code Meaning Code Meaning

00 Cloud development not observed or observable 01 Clouds dissolving or becoming less developed 02 State of sky on the whole unchanged

03 Clouds generally forming or developing 04 Visibility reduced by smoke haze 05 Haze

06 Widespread dust in suspension in the air, not raised by wind at or near the station at the time of observation. 07 Dust or sand raised by the wind at or near the station at the time of the observation, but no well-developed dust whirl(s), and no sandstorm seen: or, in the case of ships, blowing spray at the station 08 Well developed dust whirl(s) or sand whirl(s) seen at or near the station during the preceding hour or at the time of observation, but no dust storm or sandstorm

09 Dust storm or sandstorm within sight at the time of observation, or at the station during the preceding hour 10 Mist 11 Patches of shallow fog or ice fog

12 More or less continuous 13 Lightning visible, no thunder heard 14 Precipitation within sight, not reaching the ground or surface of sea

15 Precipitation within sight, reaching ground or the surface of the sea, but distant, i.e. estimated to be more than 5 km from the station 16 Precipitation within sight, reaching the ground or the surface of the sea, near to, but not at the station 17 Thunderstorm, but no precipitation at the time of observation

18 Squalls at or within sight of the station during 19 Funnel cloud(s) or tuba during the preceding hour or at time of observation

Precipitation ceased during the preceding hour

20 Drizzle (not freezing) or snow grains 21 Rain (not freezing) 22 Snow

23 Rain and snow or ice pellets 24 Freezing drizzle or freezing rain 25 Shower(s) of rain

26 Shower(s) of snow, or of rain and snow 27 Shower(s) of hail, or of rain and hail 28 Fog or ice fog

29 Thunderstorm (with or without precipitation)

30 Slight dust storm (has decreased during the preceding hour) 31 Moderate dust storm (no appreciable change during the preceding hour) 32 Sandstorm (has begun or increased during the preceding hour)

33 Severe Sandstorm (has decreased during the preceding hour) 34 Dust storm (no appreciable change during the preceding hour) 35 Sandstorm (has begun or increased during the preceding hour)

36 Slight or moderate drifting snow (generally low) 37 Heavy drifting snow (below eye level) 38 Slight or moderate blowing snow (generally high)

39 Heavy blowing snow (above eye level) 40 Fog or ice fog at a distance at the time of observation, but not at the station during the preceding hour, the fog or ice fog extending to a level above that of the observer 41 Fog or ice fog in patches

42 Fog or ice fog, sky visible (has become thinner during the preceding hour) 43 Fog or ice fog, sky obscured (has become thinner during the preceding hour) 44 Fog or ice fog, sky visible (no appreciable change)

45 Fog or ice fog, sky obscured (during the preceding hour) 46 Fog or ice fog, sky visible (has begun or has become thicker during the preceding hour) 47 Fog or ice fog, sky obscured (has begun or has become thicker during the preceding hour)

48 Fog or ice fog, sky visible 49 Fog or ice fog, sky obscured 50 Drizzle, not freezing, intermittent (slight at time of observation)

51 Drizzle, not freezing, continuous (slight at time of observation) 52 Drizzle, not freezing, intermittent (moderate at time of observation) 53 Drizzle, not freezing, continuous (moderate at time of observation)

54 Drizzle, not freezing, intermittent (heavy (dense) at time of observation) 55 Drizzle, not freezing, continuous (heavy (dense) at time of observation) 56 Drizzle, freezing, slight

57 Drizzle, freezing, moderate or heavy (dense) 58 Drizzle and rain, slight 59 Drizzle and rain, moderate or heavy

60 Rain, not freezing, intermittent (slight at time of observation) 61 Rain, not freezing, continuous (slight at time of observation) 62 Rain, not freezing, intermittent (moderate at time of observation)

63 Rain, not freezing, continuous (moderate at time of observation) 64 Rain, not freezing, intermittent (heavy at time of observation) 65 Rain, not freezing, continuous (heavy at time of observation)

66 Rain, freezing, slight 67 Rain, freezing, moderate or heavy 68 Rain or drizzle and snow, slight

69 Rain or drizzle and snow, moderate or heavy 70 Intermittent fall of snowflakes (slight at time of observation) 71 Continuous fall of snowflakes (slight at time of observation)

72 Intermittent fall of snowflakes (moderate at time of observation) 73 Continuous fall of snowflakes (moderate at time of observation) 74 Intermittent fall of snowflakes(heavy at time of observation)

75 Continuous fall of snowflakes (heavy at time of observation) 76 Diamond dust (with or without fog) 77 Snow grains (with or without fog)

78 Isolated star-like snow crystals (with or without fog) 79 Ice pellets 80 Rain shower(s), slight

81 Rain shower(s), moderate or heavy 82 Rain shower(s), violent 83 Shower(s) of rain and snow mixed, slight

84 Shower(s) of rain and snow mixed, moderate or heavy 85 Snow shower(s), slight 86 Snow shower(s), moderate or heavy

87 Shower(s) of snow pellets or small hail (slight) 88 Shower(s) of snow pellets or small hail, with or without rain or rain and snow mixed (moderate or heavy) 89 Shower(s) of hail, with or without rain or (slight)

90 Shower(s) of hail, with or without rain and snow mixed, not associated with thunder (moderate or heavy)

Thunderstorm ceased, precipitation continuing

91 Slight rain at time of observation 92 Moderate or heavy rain at time of observation 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

Thunderstorm with precipitation at time of observation

95 Light to moderate thunderstorm 96 Light to moderate thunderstorm with hail 97 Heavy thunderstorm

98 Heavy thunderstorm with dust storm 99 Heavy thunderstorm with hail

Code	Meaning	Code	Meaning	Code	Meaning
00	Cloud development not observed or observable	01	Clouds dissolving or becoming less developed	02	State of sky on the whole unchanged
03	Clouds generally forming or developing	04	Visibility reduced by smoke haze	05	Haze
06	Widespread dust in suspension in the air, not raised by wind at or near the station at the time of observation.	07	Dust or sand raised by the wind at or near the station at the time of the observation, but no well-developed dust whirl(s), and no sandstorm seen: or, in the case of ships, blowing spray at the station	08	Well developed dust whirl(s) or sand whirl(s) seen at or near the station during the preceding hour or at the time of observation, but no dust storm or sandstorm
09	Dust storm or sandstorm within sight at the time of observation, or at the station during the preceding hour	10	Mist	11	Patches of shallow fog or ice fog
12	More or less continuous	13	Lightning visible, no thunder heard	14	Precipitation within sight, not reaching the ground or surface of sea
15	Precipitation within sight, reaching ground or the surface of the sea, but distant, i.e. estimated to be more than 5 km from the station	16	Precipitation within sight, reaching the ground or the surface of the sea, near to, but not at the station	17	Thunderstorm, but no precipitation at the time of observation
18	Squalls at or within sight of the station during	19	Funnel cloud(s) or tuba during the preceding hour or at time of observation

*Precipitation ceased during the preceding hour*
20	Drizzle (not freezing) or snow grains	21	Rain (not freezing)	22	Snow
23	Rain and snow or ice pellets	24	Freezing drizzle or freezing rain	25	Shower(s) of rain
26	Shower(s) of snow, or of rain and snow	27	Shower(s) of hail, or of rain and hail	28	Fog or ice fog
29	Thunderstorm (with or without precipitation)

30	Slight dust storm (has decreased during the preceding hour)	31	Moderate dust storm (no appreciable change during the preceding hour)	32	Sandstorm (has begun or increased during the preceding hour)
33	Severe Sandstorm (has decreased during the preceding hour)	34	Dust storm (no appreciable change during the preceding hour)	35	Sandstorm (has begun or increased during the preceding hour)
36	Slight or moderate drifting snow (generally low)	37	Heavy drifting snow (below eye level)	38	Slight or moderate blowing snow (generally high)
39	Heavy blowing snow (above eye level)	40	Fog or ice fog at a distance at the time of observation, but not at the station during the preceding hour, the fog or ice fog extending to a level above that of the observer	41	Fog or ice fog in patches
42	Fog or ice fog, sky visible (has become thinner during the preceding hour)	43	Fog or ice fog, sky obscured (has become thinner during the preceding hour)	44	Fog or ice fog, sky visible (no appreciable change)
45	Fog or ice fog, sky obscured (during the preceding hour)	46	Fog or ice fog, sky visible (has begun or has become thicker during the preceding hour)	47	Fog or ice fog, sky obscured (has begun or has become thicker during the preceding hour)
48	Fog or ice fog, sky visible	49	Fog or ice fog, sky obscured	50	Drizzle, not freezing, intermittent (slight at time of observation)
51	Drizzle, not freezing, continuous (slight at time of observation)	52	Drizzle, not freezing, intermittent (moderate at time of observation)	53	Drizzle, not freezing, continuous (moderate at time of observation)
54	Drizzle, not freezing, intermittent (heavy (dense) at time of observation)	55	Drizzle, not freezing, continuous (heavy (dense) at time of observation)	56	Drizzle, freezing, slight
57	Drizzle, freezing, moderate or heavy (dense)	58	Drizzle and rain, slight	59	Drizzle and rain, moderate or heavy
60	Rain, not freezing, intermittent (slight at time of observation)	61	Rain, not freezing, continuous (slight at time of observation)	62	Rain, not freezing, intermittent (moderate at time of observation)
63	Rain, not freezing, continuous (moderate at time of observation)	64	Rain, not freezing, intermittent (heavy at time of observation)	65	Rain, not freezing, continuous (heavy at time of observation)
66	Rain, freezing, slight	67	Rain, freezing, moderate or heavy	68	Rain or drizzle and snow, slight
69	Rain or drizzle and snow, moderate or heavy	70	Intermittent fall of snowflakes (slight at time of observation)	71	Continuous fall of snowflakes (slight at time of observation)
72	Intermittent fall of snowflakes (moderate at time of observation)	73	Continuous fall of snowflakes (moderate at time of observation)	74	Intermittent fall of snowflakes(heavy at time of observation)
75	Continuous fall of snowflakes (heavy at time of observation)	76	Diamond dust (with or without fog)	77	Snow grains (with or without fog)
78	Isolated star-like snow crystals (with or without fog)	79	Ice pellets	80	Rain shower(s), slight
81	Rain shower(s), moderate or heavy	82	Rain shower(s), violent	83	Shower(s) of rain and snow mixed, slight
84	Shower(s) of rain and snow mixed, moderate or heavy	85	Snow shower(s), slight	86	Snow shower(s), moderate or heavy
87	Shower(s) of snow pellets or small hail (slight)	88	Shower(s) of snow pellets or small hail, with or without rain or rain and snow mixed (moderate or heavy)	89	Shower(s) of hail, with or without rain or (slight)
90	Shower(s) of hail, with or without rain and snow mixed, not associated with thunder (moderate or heavy)
*Thunderstorm ceased, precipitation continuing*
91	Slight rain at time of observation	92	Moderate or heavy rain at time of observation	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
*Thunderstorm with precipitation at time of observation*
95	Light to moderate thunderstorm	96	Light to moderate thunderstorm with hail	97	Heavy thunderstorm
98	Heavy thunderstorm with dust storm	99	Heavy thunderstorm with hail

From the start of 2009 columns are introduced for day of snow sleet, day of hail, day of gale and day of thunder. In the day of snow/sleet column, 5 indicates snow (and maybe also sleet) and 1 indicates sleet (but no snow). In the day of hail column, the largest applicable entry for the day is shown, the entry being

4: ice pellets/hail of less than 5 mm diameter
5: hail of 5 to 9 mm diameter
6: hail of 10 to 19 mm diameter
7: hail of more than 20 mm diameter

In day of gale, an entry of 1 indicates that the 10 minute average wind speed at 10 m height reached 34 knots. In day of thunder column, an entry of 1 indicates that thunder was heard.

Rainfall

Rainfall (or, strictly-speaking, precipitation) is measured from 0900 GMT of the previous day. A recording of ' ' or '-' indicates no precipitation. A trace (no measureable fall) is sometimes denoted by 'tr'; a trace denotes either less than 0.005 inches before 1971 and less than 0.05 mm from 1971. Sometimes there is indication that rime, dew ('w'), fog ('f'), hoar frost ('x') or wet fog ('fe') caused the trace.

From October 1978 the use of 'X' as part of the record denotes that the precipitation was the result solely of rime, dew, hoar frost or fog. After 2009 there was sometime a tendency for the `trace' measurement to be ignored - and to be replaced as a `0'.

Snow

What was recorded once as snow grains and snow pellets would now simply be regarded as snow.

From the start of 1971 the unit for total and fresh snow depth was changed from inches to centimetres.

State of ground

Before July 1960, snow cover exceeding 50% of the ground was shown as . Later, lying snow is indicated by its depth in inches (or centimetres), while several tables were used to describe the state of the ground, which are shown below:

State of ground codes from July 1960 until May 1978

Code Meaning Code Meaning Code Meaning

00 Bare plot dry 01 Bare plot dry with cracking soil 03 Bare plot dry but dew on nearby grass

10 Bare plot moist/wet with no standing water 11 Bare plot moist/wet but not muddy 12 Bare plot soft or muddy but no pools of water

20 Wet ground with small pools of water 21 Flooded, e.g. by river banks bursting 30 Bare plot frozen

31 Bare plot frozen to a depth of less than 5cm 32 Bare plot frozen to a depth of more than 5cm 40 Glaze/ice on ground without snow

50 Snow/melting snow/hail covering less than 50% of ground 60 Snow/melting snow/hail covering more than 50% of ground but not completely 70 Snow/melting snow/hail covering 100% of the ground

71 100% snow cover to a depth of under 15cm; ground underneath not frozen 72 100% snow cover to a depth of under 15cm; ground under neath being frozen 73 100% snow cover to a depth of 15cm or more; ground underneath being frozen or unfrozen

80 Loose dry snow, sand or dust covering half or more of ground, but not completely 90 Loose dry snow, sand or dust covering ground completely

Code	Meaning	Code	Meaning	Code	Meaning
00	Bare plot dry	01	Bare plot dry with cracking soil	03	Bare plot dry but dew on nearby grass
10	Bare plot moist/wet with no standing water	11	Bare plot moist/wet but not muddy	12	Bare plot soft or muddy but no pools of water
20	Wet ground with small pools of water	21	Flooded, e.g. by river banks bursting	30	Bare plot frozen
31	Bare plot frozen to a depth of less than 5cm	32	Bare plot frozen to a depth of more than 5cm	40	Glaze/ice on ground without snow
50	Snow/melting snow/hail covering less than 50% of ground	60	Snow/melting snow/hail covering more than 50% of ground but not completely	70	Snow/melting snow/hail covering 100% of the ground
71	100% snow cover to a depth of under 15cm; ground underneath not frozen	72	100% snow cover to a depth of under 15cm; ground under neath being frozen	73	100% snow cover to a depth of 15cm or more; ground underneath being frozen or unfrozen
80	Loose dry snow, sand or dust covering half or more of ground, but not completely	90	Loose dry snow, sand or dust covering ground completely

State of ground codes from May 1978 until December 1981

Code Meaning Code Meaning Code Meaning

0 Bare plot dry 1 Bare plot moist/wet with no standing water 2 Bare plot wet with some standing pools of water

3 Bare plot frozen 4 Glaze/ice on ground without snow 5 Snow/melting snow/hail covering less than 50% of ground

6 Snow/melting snow/hail covering more than 50% of ground but not completely 7 Snow/melting snow/hail covering 100% of the ground 8 Loose dry snow, sand or dust covering half or more of ground, but not completely

9 Loose dry snow, sand or dust covering ground completely

Code	Meaning	Code	Meaning	Code	Meaning
0	Bare plot dry	1	Bare plot moist/wet with no standing water	2	Bare plot wet with some standing pools of water
3	Bare plot frozen	4	Glaze/ice on ground without snow	5	Snow/melting snow/hail covering less than 50% of ground
6	Snow/melting snow/hail covering more than 50% of ground but not completely	7	Snow/melting snow/hail covering 100% of the ground	8	Loose dry snow, sand or dust covering half or more of ground, but not completely
9	Loose dry snow, sand or dust covering ground completely

From the start of 1982, two tables have been used depending on whether there is snow or ice, listed as 'table 5' and 'table 6', respectively, in a World Meteorological Organization manual on codes. The string `5/' proceeds the codes used in 'table 5'. For example, flooded ground is indicated by 5/3, because it is code 3 in the 'table 5' below. Whereas `6/' proceeds the codes used in 'table 6', so loose dry snow covering less than 50% of ground is indicated by the string `6/5'.

Table 5: state of ground codes used without snow or ice from January 1982

Code Meaning Code Meaning Code Meaning

0 Ground dry (no cracks or appreciable amounts of dust/loose sand) 1 Ground moist 2 Ground wet (standing water in small or large pools on surface)

3 Flooded 4 Ground frozen 5 Glaze on ground

6 Loose dry dust or sand not covering ground completely 7 Thin cover of loose dry dust or sand covering ground completely 8 Moderate or thick cover of loose dry dust or sand covering ground completely

9 Extremely dry with cracks

Code	Meaning	Code	Meaning	Code	Meaning
0	Ground dry (no cracks or appreciable amounts of dust/loose sand)	1	Ground moist	2	Ground wet (standing water in small or large pools on surface)
3	Flooded	4	Ground frozen	5	Glaze on ground
6	Loose dry dust or sand not covering ground completely	7	Thin cover of loose dry dust or sand covering ground completely	8	Moderate or thick cover of loose dry dust or sand covering ground completely
9	Extremely dry with cracks

Table 6: state of ground codes used with snow or ice from January 1982

Code Meaning Code Meaning Code Meaning

0 Ground predominately covered by ice 1 Compact/wet snow (with or without ice) covering less than 50% of ground 2 Compact/wet snow (with or without ice) covering at least 50% of ground

3 Even layer of compact or wet snow covering ground completely 4 Uneven layer of compact or wet snow covering ground completely 5 Loose dry snow covering less than 50% of ground

6 Loose dry snow covering at least 50% of ground 7 Even layer of loose dry snow covering ground completely 8 Uneven layer of loose dry snow covering ground completely

9 Snow covering ground completely; deep drifts

Code	Meaning	Code	Meaning	Code	Meaning
0	Ground predominately covered by ice	1	Compact/wet snow (with or without ice) covering less than 50% of ground	2	Compact/wet snow (with or without ice) covering at least 50% of ground
3	Even layer of compact or wet snow covering ground completely	4	Uneven layer of compact or wet snow covering ground completely	5	Loose dry snow covering less than 50% of ground
6	Loose dry snow covering at least 50% of ground	7	Even layer of loose dry snow covering ground completely	8	Uneven layer of loose dry snow covering ground completely
9	Snow covering ground completely; deep drifts

Visibility

It wasn't until January 1960 that regular visibility measurements were made. Observations were represented by codes, the code denoting the lowest applicable visibility being used. The visibility codes used until May 1978 were:

Visibility Code Visibility Code Visibility Code

25m A 50m B 100m C

200m D 400m E 1km F

2km G 4km H 7km I

10km J 20km K 30km L

40km M

Visibility	Code	Visibility	Code	Visibility	Code
25m	A	50m	B	100m	C
200m	D	400m	E	1km	F
2km	G	4km	H	7km	I
10km	J	20km	K	30km	L
40km	M

From June 1978 the visibility codes used are:

Visibility Code Visibility Code Visibility Code

<20m X 20-39m E 40-90m 0

100-190m 1 200-390m 2 400-900m 3

1000-1900m 4 2-4km 5 5-9km 6

10-19km 7 20-39km 8 ≥40km 9

Visibility	Code	Visibility	Code	Visibility	Code
<20m	X	20-39m	E	40-90m	0
100-190m	1	200-390m	2	400-900m	3
1000-1900m	4	2-4km	5	5-9km	6
10-19km	7	20-39km	8	≥40km	9

Wind direction

In calm conditions the wind directions should have been recorded as `00'. Otherwise the direction (in degrees) should have been divided by 10, so that East - which is 090 degrees - was recorded as `09'. North was taken as 360 degrees, and so it should have been recorded as `36'. However, at times there is a tendency to use the compass points, such as N or NE. And after 2008 there are occasions when whole degrees are used, so that 090 is used instead of 09 to indicate a wind from the east.

Wind speed

Until December 1959, wind speed was measured in Beaufort wind scale, as shown in the table below:

Beaufort force Wind speed (knots) Beaufort force Wind speed (knots) Beaufort force Wind speed (knots)

0 <1 1 1-3 2 4-6

3 7-10 4 11-16 5 17-21

6 22-27 7 28-33 8 34-40

9 41-47 10 48-55 11 56-63

12 64+

Beaufort force	Wind speed (knots)	Beaufort force	Wind speed (knots)	Beaufort force	Wind speed (knots)
0	<1	1	1-3	2	4-6
3	7-10	4	11-16	5	17-21
6	22-27	7	28-33	8	34-40
9	41-47	10	48-55	11	56-63
12	64+

And from May 1960 wind speed was measured in miles per hour (mph), rather than knots. The symbol `-' is sometimes used to denote calm.

As well as wind speed, from November 1960 the run of wind is given. This is integral of wind speed over time from 0900 GMT of the previous day until the 0900 GMT of the current day. The `diff from previous day' is the run of wind for current measurement minus the value from the previous day. The unit for both measurements is nearly always miles. Where a second value is provided, it is the hourly-mean value.

Before March 1972, the cup counter can be assumed to be 25 feet high, unless it is stated to be at 2m. After this period there shouldn't be any run of wind measurements at 25 feet.