When I learnt to fly it was Oktas and I felt that was dead easy 4 Oktas meant 1/2 the sky was obscured but we then moved to Few, SCT, etc
I think this is a retrograde move. In fact when I ask a student or for that matter the majority of recreational pilots that I come across how much cloud cover is say BKN they haven’t a clue.
So I feel this was a detrimental move with respect to safety so could anyone tell me why the change was made?
The abbreviations were probably found more intelligible in encoded reports. The undesirable alternative would have assembled numerical information for the amount and the layer (mass) height. In practice the precision afforded by oktas is excessive and, other than the extremes of SKC or OVC, there are only three cases to remember. The cloud amount reporting accuracy is also only something like +/- 2 oktas (details in an appendix to ICAO Annex 3).
These abbreviations must pre-date METARs and TAFs because they’re included in the US Airman’s Information Manual, issue 1, 1976. They appear to have been introduced in the early 1990s? From Flying magazine, Oct 1993, pp 100–102:
Changing Weather
New codes aim to make aviation forecasts easier to understand.
By John GabrielThey’ve gone and done it again.
Now that they’ve changed the
airspace designations (some-
thing that has always caused problems
for private pilot candidates) they’ve
turned their attention to another per-
petual pilot problem—the format for
airport weather observation and fore-
casts. But not to worry. The new codes,
the result of an international effort to
reduce confusion and misunderstand-
ing, really are easier to understand and
interpret. The new reporting formats
are in conformity with International
Civil Aviation Organization (ICAO)
standards.
In general, the new reports will con-
tain more information and less abbre-
viation; or at least use more obvious
abbreviations. For example, wind di-
rection is listed with three digits rather
than two, and wind velocity is labeled
as knots under the new format. When
you see 22015G25KT on a new-style
report, you will know that the wind is
from 220 degrees at 15 knots, gusting
to 25 knots. The old system would have
reported wind as 2215G25. Under the
old system you knew the numbers
referred to wind because of their place-
ment in the airport observation se-
quence report and you had to remem-
ber to add a zero to the wind direction
to find the actual number. The new
method is definitely clearer.
Reporting abbreviations for cloud
cover and height are also easier to un-
derstand. SKC means SKy Clear; SCT
is SCaTtered; BKN is BroKeN; and
OVC is OVerCast. The cloud height is
given in three digits indicating hun-
dreds of feet above the airport surface.
BKN020 indicates a broken layer of
clouds at 2,000 feet. The new report
will also identify the type of clouds if
significant. BKN025CB will mean there
is a broken layer of cumulonimbus
clouds over the airport. If clouds are
obscured a vertical visibility (VV) will
be reported in hundreds of feet.
The implementation of the new inter-
national codes for terminal forecasts
(TAFs) and airport sequence reports
(METARs) is occurring in two stages.
On July 1, 1993, the world aviation me-
teorology community began using the
new METAR and TAF codes, while the
U.S. began encoding 250 “landing
rights” airports to the new METAR
code for international dissemination.
The present North American encoded
data remains controlling for things like
dispatch and alternate selection. The
80 U.S. international airports that had
been required to prepare forecasts in
the old TAF format are now preparing
them in the new codes. International
forecasts and reports prepared by the
U.S. for parts of the North Atlantic,
Gulf of Mexico/Caribbean area and Pa-
cific routes are now using the new
METAR and TAF codes.
The second phase of the conversion,
due to take effect on January 1, 1996,
would involve the U.S. switching com-
pletely to the new METAR and TAF
codes and completely eliminating the
current North American observation
and forecasts formats.
The World Meteorological Organiza-
tion has published a 62-page guide to
the new codes called “Aerodrome Re-
ports and Forecasts, a users’ handbook
to the codes.” The publication, WMO-
No. 782, can be obtained from the
American Meteorological society, Attn:
WMO Publications Center, 45 Beacon
Street, Boston, Massachusetts 02108,
at a cost of $16 plus $5 shipping and
handling.
The division by eights was introduced in UK and western Europe on 1 Jan 1949 when the system of tenths was abandoned. That was also when QNH was introduced, wind speeds were to be reported in knots instead of Beaufort numbers, and the compass was to be divided into 36 intervals of ten degrees instead of 32 points. (The Aeroplane, vol. LXXV No. 1959, 24 Dec 1948. *)
