About Meteorological Observations
Curious about the tools and notations used for weather observations? Have you started transcribing and want to know what it all means? Wondering what a barometer is? You found the right page! Learn more about the instruments used to take measurements, types of observations, and common abbreviations.
Instruments used to take measurements
- The barometer measures the atmospheric pressure. When the pressure from different locations is mapped, the patterns tell us how the atmosphere is behaving. Barometer readings can tell us where the winds are coming from, and whether they are likely to bring us colder or warmer weather, rain or snow, storms or clear skies.
- Interested in learning how pressure measurements from a barometer are corrected? Check out the following video:
Wet bulb thermometer/Dry Bulb thermometer
- Wet and Dry bulb thermometers are used to measure the humidity in the air. The differences in these measurements are used to calculate vapour pressure, relative humidity and dewpoint.
- To measure the direction of the wind a wind vane is used.
- To measure the speed of the wind an anemometer is used by clocking the distance the wind turned the anemometer in a given time.
- At the McGill Observatory, the wind was measured by methods which varied over time, and were often kept in a separate logbook. As a result, the anemometer columns are often empty, except for the period from 1884 to 1900, when instead of recording wind measurement, the observers entered the barometer and attached thermometer readings from Montreal’s City Hall. While this might have been an efficient use of the logbook page for the 19th century observers, it can cause lots of confusion for 21st century researchers and citizen scientists!
- Interested in how to interpret wind speed? Check out this handy resource from the US National Oceanic and Atmospheric Administration: The Beaufort Wind Scale
- Thermometers are used the measure temperature. Each instrument had a unique set of calibration errors, so there are columns for both the original observation and corrected value.
- The minimum temperature usually occurs at the end of the night, towards sunrise, while the maximum temperature is usually towards the middle or end of the afternoon, around 3pm. They are only recorded once per day (so most of the time the columns are blank in the logbooks/ledgers/registers!).
Types of Observations
No fancy instruments were used to classify cloud types, instead observers compared what they saw in the sky to images of clouds.
They were classified into types, described by their appearance, height, and whether they produced rain, snow or other types of precipitation.
The clouds are divided into two layers; upper and lower, and for each layer the cloud type, the direction the clouds are coming from, and the amount were recorded by observers
“Weather” might seem like one of the most important observations, but could be much harder to record and classify than numbers which could be read off an instrument. In the earliest logbooks, the weather at the time of observation was written out (such as “Rain” or “Fog”), but in the late 1870s international symbols began to be used (with some special Canadian variations).
Phenomena is where observers would record anything observed in the sky such as rainbows, haloes, or other optical events. They would use symbols to record them (You can check out the symbols and what they mean below).
Also known as the northern lights, an aurora is a naturally occurring light show resulting from particles from the earth and sun’s atmospheres colliding. Observers would classify them by intensity and classes I-IV.
Abbreviations and Symbols
- N - North
- NNE - North North East
- NE - North East
- E – East
- ESE – East South East
- SE – South East
- SSE – South South East
- S – South
- SSW – South South West
- SW – South West
- WSW – West South West
- W – West
- WNW – West North West
- NW – North West
- Ci/C - Cirrus: high and wispy clouds
- Ni/N - Nimbus: produces precipitation
- St/S - Stratus: a flat layer of cloud
- Cu/K – Cumulus: puffy pile of cloud
- Cust – Cumulo-stratus
- Cicu – Cirrus-cumulus
- Clear – Indicates clear sky.
- Hid/Hidden – Cannot see, usually due to darkness.
- Fog/Foggy – Used when the observer is surrounded by fog
- Haze – Used when mist or haze, consisting of condensed vapour, intervenes between the eye and the sky.
- Smoke – Indicates the presence of smoke.
Observers sometimes used symbols or abbreviations to describe the weather with fewer words. Sometimes a letter and a symbol are associated to a single weather description, sometimes only a letter or only a symbol is attributed to the weather pattern. The table below lists common symbols used in the weather records.
|Beaufort Letter||International Symbol||Meaning|
|b||...||Blue sky, cloudless.|
|c||...||Cloudy, but detached opening clouds.|
|...||Mysty; i.e. hazy, caused by condesned vapour aloft.|
|g||...||Gloomy, dark weather.|
|...||Flurries of snow.|
|u||...||"Ugly". Threatening appearance.|
|...||Unusual visibility of distant objects.|
Notes on Letters and Symbols
Degrees of intensity may be indicated by the exponents 0 or 2 attached to a symbols or letters.
The letter 'b', unaccompanied by any other letter or symbol, indicates a clear sky. Altough originally chosen because a clear sky during daylight is ordinarily blue, the letter 'b' may also be used when the sky is clear at night, or whenever from any cause the sky, though not blue, is clear.
'bc' denotes the presence of a few detached clouds, the clear part of the sky being greatly in excess of the part that is clouded.
'c' alone denotes detached clouds with clear spaces intervening; but it is not necessary that the cloudy part of the sky should exceed the part that is clear.
>> Fog - 'f'
'f' is used when the spectator is completely surrounded by fog.
>> Misty or haze
The 'misty' symbol is used only when mist or haze, consisting of condensed vapour, intervenes between the eye and the sky.
>> Dust haze
The symbol for dust haze is to be used when the clearness of the sky is dimmed by dust floating aloft.
>> 'd' and 'p'
'd' for drizzle, indicates that the rain is composed of very small drops, without reference to its being transient or continued, while 'p', for passing showers, shows that the rain falls in frequent showers of short duration, which may be either heavy or light for the time they last.
'r' in the weather column indicates the fact that rain is falling, without implying that the drops were exceptionally small, as in a drizzle, and also that the fall is fairly continuous (i.e. not frequently interrupted). This said, 'r' does not necessarily express rain of long duration.
'q' expresses a squall or squalls (i.e. rather strong wind of short duration) while the combination of 'pq' expresses squally with rain.
>> 'g' and 'u'
While 'g' denotes weather that is gloomy but not necessarily threatening, 'u' (for "ugly") indicates that the weather is threatening without implying that it is necessarily dark, as the absence of sunshine is not a necessary element of a threatening aspect in the sky.
>> Hail - 'h'
'h' and the hail symbol is to be used for hail, whether the stones be large or small, provided that they be of crystalline structure.
>> Soft hail
The soft hail symbol is used for stones that are small, like snow pellets, without crystalline structure. The term "soft" is not so applicable in Canada as it is in England, where the name originated. When mixed with rain it often bears the name of "sleet".
>> Flurries of snow
This term denotes passing showers of snow. Very light and very heavy flurries may be expressed by applying exponents.
>> Ice crystals
These are minute crystals of ice that are occasionally seen apparently floating in the air, and glistening in the sun's rays. They are chiefly observed during bright weather with hard frost.
>> Visibility of distant objects
This term has no reference to the clearness of the sky, as the condition which it expresses may exist whether the sky be cloudy or not, and is most frequent when the general character of the sky is threatening. It often occurs also between heavy rain showers. The symbol used above for "visibility" has been substituted for 'v', on account of the resemblance of the latter to that adopted for "silver thaw" by the Vienna Congress.
>> Lightning - 'l'
The "lightning" symbol is used when lightning occurs without thunder.
>> Silver thaw
Phenomenon of frozen moisture on trees or other objects when the weather suddenly becomes warm after great cold.
>> Glazed frost
This term is applied to the glazed surface formed on the ground, trees, and other objects by rain falling and immediately freezing thereon. It differs from "silver thaw" in this respect, that the latter is formed by the condensation of vapour, and consequently has not the same smooth surface.
READING THE LOGBOOK
For more detailed instructions on how weather observations were recorded, have a look at the original meteorological standards here.