"Phil Layton" wrote in message
...
We were doing quite well this morning with a steady flow rate matching the
actual landing rate. However this afternoon we had to change runways twice
as the front just nudged enough E to bring us 'Westerlies' for an hour.
This can be seen from the METARs:
EGLL 081750Z 12009KT 9999 FEW033 BKN044 07/06 Q0967
EGLL 081720Z 11006KT 080V150 9999 BKN042 08/06 Q0966
EGLL 081650Z 12006KT 090V230 9999 FEW034 BKN042 09/06 Q0966
EGLL 081620Z 22006KT 190V280 9999 FEW021 SCT034 09/05 Q0966
EGLL 081550Z 21007KT 9999 FEW034 SCT041 09/05 Q0966
EGLL 081520Z 15008KT 9999 FEW026 SCT036 09/06 Q0965
EGLL 081450Z 15009KT 9999 FEW009 SCT018 BKN030 08/06 Q0965
EGLL 081420Z 13012KT 9999 FEW010 SCT017 BKN025 08/06 Q0965
EGLL 081350Z 13012KT 9999 FEW009 BKN015 07/05 Q0965 TEMPO BKN012
Holding delays went up as a result.

Not predicted on the TAF, Jon, but I guess it might have deserved a Prob10
in the days we used to have them!

Phil

Not guilty m'lord on this occasion !

From a TAF perspective it all depends on the the extent of the change in
terms of degrees and also the speed before and after the change. However, in
this case it a change to 130° to 210° would be valid in the TAF as it was a
swing of 60° or more and the wind was over 10KT before it veered - but no
doubt difficult to predict accurately for such a short time. If you were
writing a TAF based on the what happened it would quite awkward, either a
short BECMG of a SW'ly immediately followed by another short BECMG back to a
SE'ly or alternatively a TEMPO SW'ly for 1 hour. Either way it's a difficult
one to convey well within the constraints of the TAF rules.

As an aside, have you tried the Openrunway service for Heathrow, Phil ? I'm
sure you'd find that interesting and it also provides hourly predictions for
wind speed and direction amongst other parameters
http://www.metoffice.gov.uk/aviation...rts/openrunway

Jon.