WAFC london forecast validity

[B777_my]

anyone can enlighten me of the validity of these charts? its shows 0000, 0600,1200,1800. but does it valid at 0000utc itself or like the australian charts that valid +-3hrs of the validity time. thanks

[bflyer]

Hi...i believe it is valid at the times mentioned..i.e...valid at 0000 UTC..etc
but then again let's wait for a more informed opinion

[alatnariver]

As I have learned, the SIGWX and wind charts produced by the WAFC London are showing the forecasted situation for the time indicated only. If you would like to call this validity, well then I guess these charts are valid only at the specified time indicated.

However just take the charts that are available during dispatch of a flight covering the time during which the flight is operated.

[B777_my]

WAFC london

quote from aus AIP GEN3.5
-----------------------------------
20. SIGNIFICANT WEATHER CHARTS
...
20.3 The availability of the Australian area significant weather charts
and validity times are as follows:
Appropriate Availability Time (UTC) Validity Time (UTC)
0100 1800
0700 0000
1300 0600
1900 1200
20.4 Significant variations during the period validity time
plus or minus three hours
are included. Amendments between routine issues
are normally narrative advices of variations, but they may be
incorporated in a new chart.
-------------------------------------
about the WAFC london i only got this
http://www.metoffice.gov.uk/research...ar03/wafc.html
quote:
...In addition, the following charts will appear with the same header every six hours, with a validity time 13 1/2 hours later: PGAE06, PGCE06...
;;
i am not sure weather the chart only valid at the valid time like a snapshot...perhaps anyone could supply me with a reference. Thanks

[bookworm]

It's an interesting question. I believe WAFC SigWx charts are a snapshot. Here's what Annex 3 App 2 says:

1.3.1 Forecasts of significant weather phenomena
prepared by WAFCs shall be issued four times a day for fixed
valid times of 0000, 0600, 1200 and 1800 UTC.

It doesn't rule out the idea of a validity window, but I believe there is no requirement, nor intent, to provide one. I can't find anything relevant in the SADIS User Guide, except similar wording to the above.

[InSoMnIaC]

I think I read somewhere that the london issued sigwx charts have a validity period of 4 hours before until 5 hours after the stated validity time.

its not a snapshot of the wx at the particular valid time as it is issued ahead of time.

[bookworm]

I think I read somewhere that the london issued sigwx charts have a validity period of 4 hours before until 5 hours after the stated validity time.

The Low Level (< FL100) SigWx charts issued by London (Forms 215 and 415) have exactly that validity -- it's printed on the chart. But I don't think the Mid and High Level SigWx have any such validity window.

its not a snapshot of the wx at the particular valid time as it is issued ahead of time.

That doesn't follow. By "snapshot" all we mean is that only weather forecast to occur at the validity time is shown on the chart. The Low Level charts will show weather forecast to disappear before or appear after the validity time for the fronts and zones as well. So for example today the F215 with fronts shown for 1800Z says "ISOL CB 020/XXX FAR N TL 17Z", because the validity window is 1400 to 2300Z. If it were a "snapshot" at 1800 it wouldn't show such weather.

[robin747]

Sig Wx charts Validity

As per WMO convention the validity for SigWx charts is 6-9 hrs.
UK Met office revised the validity considering the flight duration times for most users. So, if the vaild time is 1200z it is valid from 0800-1700z [ 4hrs before and 5 hrs after] The issue time is of no relevance except for the overall picture as they are issued 12-14 hrs prior to vaild times.

http://www2.metoffice.gov.uk/aviatio...s/details.html

[bookworm]

robin747

The charts referred to in your link are the low level SigWx charts issued by the Met Office for UK domestic consumption. B777_my is asking about the medium and high level SigWx charts issued by the Met Office acting in its capacity as WAFC London.

I'll ask.

[robin747]

SigWx charts

<WAFS convention states all
fixed time charts are regarded as being valid from 3 hours prior to the
fixed time to three hours after the fixed time.>

[LYKA]

UK AIP (23 Nov 06) GEN 3-5-13

Issue times: Validity Times

1100 0000
1700 0600
2300 1200
0500 1800

Charts cover the period within 3 hours either side of the quoted fixed time, except 215 charts and surface isobaric charts, which are
valid for the time specified.