Quickie please.

When reporting past weather in the weather group beginning with 7

i.e 762w1w2

is w1 weather obs the past hour
and
w2 weather obs in past 3 hours ?

Thanks

Phil

--
www.layton.me.uk/meteo.htm

"Phil Layton" wrote in message
...

When reporting past weather in the weather group beginning with 7
i.e 762w1w2
is w1 weather obs the past hour
and
w2 weather obs in past 3 hours ?

.... not quite as straightforward ... the full regs are quoted below and
are available from the WMO web site, but is essence, as you are
(presumably) looking at SYNOP's from 'main' hours (00,06,12 & 18Z), the
the period covered by both in combination is 6 hours.

Martin.

12.2.6.6 Past weather reported from a manned weather station: W1W2

12.2.6.6.1 The period covered by W1 and W2 shall be:

(a) Six hours for observations at 0000, 0600, 1200 and 1800 UTC;

(b) Three hours for observations at 0300, 0900, 1500 and 2100 UTC;

(c) Two hours for intermediate observations if taken every two hours.

12.2.6.6.2 The code figures for W1 and W2 shall be selected in such a
way that W1W2 and ww

together give as complete a description as possible of the weather in
the time interval

concerned. For example, if the type of weather undergoes a complete
change during the

time interval concerned, the code figures selected for W1 and W2 shall
describe the

weather prevailing before the type of weather indicated by ww began.

12.2.6.6.3 When W1 and W2 are used in hourly reports other than those
covered by Regulation

12.2.6.6.1 (a) and (b), they cover a short period of time and Regulation
12.2.6.6.2

shall apply.

12.2.6.6.4 If, using Regulation 12.2.6.6.2, more than one code figure
may be given to W1 with regard

to the past weather, the highest figure shall be reported for W1 and the
second highest

code figure shall be reported for W2.

12.2.6.6.5 If the weather during the period has not changed so that only
one code figure may be

selected for the past weather, then that code figure shall be reported
for both W1 and W2.

For example, rain during the entire period shall be reported as W1W2 =
66.

12.2.6.7 Past weather reported from an automatic weather station :
Wa1Wa2

12.2.6.7.1 The period covered by Wa1Wa2 shall be :

(a) Six hours for observations at 0000, 0600, 1200 and 1800 UTC;

(b) Three hours for observations at 0300, 0900, 1500 and 2100 UTC;

(c) Two hours for intermediate observations if taken every two hours.

12.2.6.7.2 The code figures for Wa1Wa2 shall be selected so that the
maximum capability of the automatic

station to discern past weather is utilized, and so that Wa1Wa2 and wawa
together

give as complete a description as possible of the weather in the time
interval concerned.

12.2.6.7.3 In cases where the automatic station is capable only of
discerning very basic weather

conditions, the lower code figures representing basic and generic
phenomena may be

used. If the automatic station has higher discrimination capabilities,
the higher code

figures representing more detailed explanation of the phenomena shall be
used. For

each basic type of phenomenon, the highest code figure within the
discrimination

capability of the automatic station shall be reported.

12.2.6.7.4 If the type of weather during the time interval concerned
undergoes complete and discernible

changes, the code figures selected for Wa1 and Wa2 shall describe the
weather

prevailing before the type of weather indicated by wawa began. The
highest figure shall be

reported for Wa1, and the second highest code figure shall be reported
for Wa2.

12.2.6.7.5 If a discernible change in weather has not occurred during
the period, so that only one code

figure may be selected for the past weather, then that code figure shall
be reported for both

Wa1 and Wa2. For example, rain during the entire period shall be
reported as Wa1Wa2 = 44

in the case of an automatic station incapable of differentiating types
of precipitation, or

Wa1Wa2 = 66 in the case of a station with the higher discrimination
capability.



--
FAQ & Glossary for uk.sci.weather at:-
http://homepage.ntlworld.com/booty.weather/uswfaqfr.htm
and
http://booty.org.uk/booty.weather/metindex.htm

"Martin Rowley" m wrote in
message ...
"Phil Layton" wrote in message
...

When reporting past weather in the weather group beginning with 7
i.e 762w1w2
is w1 weather obs the past hour
and
w2 weather obs in past 3 hours ?

... not quite as straightforward ... the full regs are quoted below and
are available from the WMO web site, but is essence, as you are
(presumably) looking at SYNOP's from 'main' hours (00,06,12 & 18Z), the
the period covered by both in combination is 6 hours.

Martin.

Thanks Martin. Thats useful.

I take it then when only w1 is reported, that the condition didn't last for
longer than 50% (i.e 3hrs of a main hour ob) of the time, otherwise it
would have been reported twice W1w2.

Phil