Weather Code, December 1, 1896
U. S. Department of Agriculture, Weather Bureau.

Perhaps the leading feature of meteorological codes, of any era, is their sequential ordering of observations, one notation after another —

Data for transmission by telegraph will be enciphered in the following order :

1. Name of station (or telegraphic designation therefor, as furnished from the central office).
2. Pressure and temperature (corrected readings).
3. Precipitation.
4. Direction of wind, state of weather, and wet thermometer.
5. Current wind velocity and minimum temperature, or current wind velocity and maximum temperature.
6. Minimum or maximum temperature (in twenty-four hours) which occurred more than twelve hours previous to observation.
7. Marked rise or fall of pressure (from stations specially designated).
8. Report on the river observation (from stations specially designated and in certain authorized reports).
9. Frost (light, heavy, or killing).
10. Thunderstorms.
11. Fog, haze, or smoke.
12. Upper clouds.
13. Lower clouds (when sent).
14. Maximum wind velocity and direction (in accordance with special instructions).
15. Special monthly or weekly reports.

A "Description of the code" appears on pp 8-9, followed by instructions in successive order for each of the categories of data listed above (leaving out only the straightforward abbreviations for station, e.g., Angeles for Los Angeles, Fuca for Port Angeles, Washington).

The instructions for each category have to do with both observations and their coding. Each instruction refers implicitly to the code sections in the back of the book, that might be called "tables".

As seen in the Barometer table shown above, the Weather Code does list codewords. Yet these codewords are selected with a view to the cipher-like functions of their successive syllables. The "Description" elaborates the principles :

12. The code is printed in such a manner that observers may be enabled to translate the reports without using the book, provided they have made a careful examination of the key. It is a simple arrangement of consonants and vowels of the alphabet in the series of words, so as to be readily translatable at sight. (Date words and several other special lists of words which are seldom used, do not conform to the key.)

To aid the memory it should be observed that these values increase regularly, according to the order of the letters in the alphabet.

The values of the respective consonants and vowels are as follows :

14. In deciphering, it will be noticed that words beginning with vowels indicate that the value under consideration is less than .10, or calm, etc. In cases where the temperature, etc., is less than 10°, etc., it should be noticed that the consonant immediately preceding the second vowel is one which has no value in the code, that is, it is neither B, D, F, G, M, N, R, S, nor T, and consequently is to be ignored in translating.

One needs to see and study the "tables," in order to develop confidence that translation can be achieved without the book. It is done by meticulous, step-by-step, ergodic construction of a message.

Some stations adjusted their reports for local conditions, e.g., proximity to a major (floodprone) river. Moreover, reports from stations in cotton, sugar and rice regions, and in corn and wheat regions, forwarded their reports to section centers where, to take the example of the former case, mean maximum and minimum temperatures, and rainfall might be averaged and then sent out over regional circuits.

Six examples on pages 23-24 illustrate the use of the code in different circumstances and meeting different requirements.

1. Example 1.—Regular 8 a.m. report.
2. Example 2.—Regular 8 a.m. report from a river station where cirrus clouds were observed moving from an abnormal direction previous to the observation and all the precipitation occurred before 8 p.m. the previous day.
3. Example 3.—Regular Tuesday morning report, in winter, from a station instructed to send snow and ice data, but that does not telegraph 8 p.m. reports.
4. Example 4.—Regular 8 p.m. report.
5. Example 5.—Regular 8 p.m. report for the last day of the month.
6. Example 6.—Regular 8 a.m. report when there is no wind, state of weather clear, no precipitation, the minimum temperature recorded twelve hours previous was lower than at the current observation and cirro-stratus clouds were observed within one hour previous.

A separate example is given on page 22 of a coded report of "special observations," which is presented below —

The example is similar in format to the six examples of ordinary reports described previously. It is followed by instructions about filing and recording, including this —

137. The observer or assistant filing such messages will politely notify the telegraph manager or receiving clerk that the message is a Government message, to which priority in transmission over all private messages is secured by law; that it calls for immediate transmission; and that it is of such special importance that delay in forwarding it may result in serious public disaster.
 

afterword

The Weather Code was updated periodically; LC lists editions for 1913, 1924, 1931, 1939 (numeral system)*, 1942 (numeral system, possibly a wartime abridgement of the 1939 code), 1956 and 1961. To these might be added similar codes like the 1930 Aerological Code (pilot balloons), and Codes for Cloud Forms and States of the Sky according to the International System of Classification* (Weather Bureau Circular S, W.B. No. 1249., 1938). There were also codes for ship's weather observations, and coded teletype symbol weather reports*.
* indicates codes that are now or will soon be treated in these pages.

back to meteorological codes.

26 feb 06