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UNITED STATBS DEPARTMBM OF COMMBRCE
WEATHER 1BUREAU TOPICS AND PERSONNEL
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AUGUST 1944
INFORMATION
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DIFFERENCES IN WEATHER TERMINOLOGY BETWEEN BRITISH AND U. S,
USAGE
In a recent circular to weather offices the Controller of Canadian Meteorological
Services called attention to oertain importaiit differences in
meteorological practices and definitions that exist between North America
and other parts of the world, particularly in the British Empire.
This information may be of considerable interest to officials of the Weather
Bureau having contact with foreign pilots and other personnel or briefing
U. 5. pilots for missions into othor countries. Most of thme distinctions
have been pointed out in various Weather Bureau circulars
When the International Numeral Code and “Present Weather” tables
Were introduced about 1989. However, since that time there haa been
an increasing number of contact8 with personnel not accustomed to our
Practices, and it appears desirable to call attention again to the important
difforencos. Tho following is taken largely from the Canadian Meteorological
Service Circular :
1. The British use the term rcfog” to denote any obstruction to vision, xvducjng
the visibility to lees than 1100 yards, irrespective of whether it is caused by
emoke, dust particles, or water dropleta. The word rrfog” is never ueed in Inkrnational
practices when visibility is 1100 yards or more. For vieibility 1100
yards to 2200 yards the word “rniatpJ (in British Air Ministry meteorological pmctice,
mist and drizzle are distinct phenomena) or haze” is applied, depending on
the mlative humidity. For visibility 2200 yards or mom the word 11 hams’ may be
used.
In mgard to visibility below 1100 gnrde, the Intarnational c r ~ ~ code p p makes
speciflo provieion (I‘ ww” equals 80-49) for the meteorological phenomena of
dust storins, Band storms, and storms of drifting or blowing snow. In all other
caw of visibility bolow 1100 yards, tho International Code uses the rlww” decade
40-4 in conneation with fog or thick ham produced by dust (not currently blown
by etrong surface winds).
2, The British doanition of tt81eetJJ refom to precipitation of mdting mow and
rain or of rain and snow together. “SleetJ’ In U. 8. terminology represents froeen
rain dropa.
3. In British torminology the phrase “soft hail” would daeoribe the phenomena
called ((snow pellets” in North America.
4. The ooncept of ceiling as defined in Circular N is not used at Air Ministry
&teoroiogical Offlw, either in forecaste or at pilot brieflnp, and is not generally
understood in oountria outside North America.
Olouds arealways reported in amordance with International Oode Tabla
(ULC~U,), Nh and Nh. The words “scattered” ana “brdken” to describe the sltg
Oandition are not used hi Great Britain and other countdell outeide of Xorth Amor.
In the Benee in which they are uaed in the airways reports in the United Stam,
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