Proposal to Align the Issuance Time of Wafs SIGWX Forecasts

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WAFSOPSG/5-WP/17
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International Civil Aviation Organization
WORKING PAPER / WAFSOPSG/5-WP/17
23/6/09

WORLD AREA FORECAST SYSTEM OPERATIONS GROUP (WAFSOPSG)

FIFTH MEETING

Paris, France, 16 to 18 September 2009

Agenda Item / 5: / Operation of the WAFS
5.6: / Other issues related to the operation and implementation of the WAFS

PROPOSAL TO ALIGN THE ISSUANCE TIME

OF WAFS SIGWX FORECASTS

(Presented by the WAFC Provider States)

SUMMARY
This working paper presents a proposal to align the issuance time of WAFS SIGWX forecasts in order to overcome concerns expressed by some members at the WAFSOPSG/4 Meeting.

1.INTRODUCTION

1.1The group will recall that the WAFSOPSG/3 Meeting formulated Conclusion 3/14 calling on the WAFC Provider States to advance, in time for the WAFSOPSG/4 Meeting, the lead time of issuance of SIGWX forecasts in the BUFR code form to:

a)17 hours for high levels (SWH); and

b)16 hours for medium levels (SWM).

Whilst not explicitly mentioned in Conclusion 3/14, portable network graphics (PNG) SIGWX products are to be issued with a lead time of 16 hours. When operating in back-up mode, SWM BUFR and all PNG charts are issued with a lead time of 15 hours.

1.2The WAFC Provider States implemented these changes in February 2008 in accordance with Conclusion 3/14.

1.3At the WAFSOPSG/4 Meeting, some members raised concerns that should Volcanic Ash (VA) or Tropical Cyclone (TC) advisory information become available from a designated VAAC or TCAC between issuance of the SWH BUFR (at 17 hours ahead of validity) and issuance of the SWM BUFR and all PNG charts (at 16 hours ahead of validity), the WAFCs are not required to incorporate the new information on the latter set of products. Instead, the new information would be taken into account on the subsequent set of products issued 6 hours later. This working arrangement is to ensure that SWH and SWM BUFR and PNG products are entirely consistent, as per the user requirement.

1.4The WAFCs share the above concerns expressed, and accordingly propose to align the issuance times of WAFS SIGWX forecasts in the BUFR code and PNG chart forms.

2.Proposal to align the issuance time of WAFS SIGWX

2.1All SIGWX products should contain consistent information, particularly with regards VA and TC. Any new VA or TC advisory information arriving after the nominal issue time will be reflected in subsequent product issuances.

2.2In light of the concerns expressed at the WAFSOPSG/4 Meeting, the WAFCs have reconsidered their working practices and are now confident that they would be capable of issuing all SIGWX products at 17 hours ahead of validity time during normal modes of operation. During back-up modes of operation, however, owing to the additional time required to generate the contingent set of WAFC products, the WAFCs would still require a buffer zone of 2 hours to prepare and issue the routine and contingent set of SIGWX products.

2.3WAFS SIGWX backup tests are conducted by each WAFC on a quarterly basis. This means that over a 12 months period, eight SIGWX back-up tests are conducted (i.e. four by each of the two WAFCs). This equates to <0.3 percent of the total number of product issues per year. Of course, a short notice back-up may be called at any time; however such instances are extremely rare (typically once per year on average), and would not impact this percentage greatly.

2.4Accordingly, the WAFCs propose to align the issuance times of WAFS SIGWX as follows:

PRODUCT / CURRENT / PROPOSED
Normal issue time / Contingency issue time / Normal issue time / Contingency issue time
SWH BUFR / T-17 hours ahead of VT / T-17 hours ahead of VT / T-17 hours ahead of VT / T-15 hours ahead of VT
SWH PNG / T-16 hours ahead of VT / T-15 hours ahead of VT / T-17 hours ahead of VT / T-15 hours ahead of VT
SWM BUFR / T-16 hours ahead of VT / T-15 hours ahead of VT / T-17 hours ahead of VT / T-15 hours ahead of VT
SWM PNG / T-16 hours ahead of VT / T-15 hours ahead of VT / T-17 hours ahead of VT / T-15 hours ahead of VT

2.5Notable changes from the current issues times are highlighted in bold underscored italics. It is important for the group to recognise that, during period of contingency (i.e. backup mode), the above proposal would mean that SWH BUFR would be issued 2 hours later than currently during. However, by issuing all of the products at the same nominal hour (i.e. 17 hours ahead of VT in standard mode and 15 hours ahead of VT in contingency mode), the content of the products would be consistent – e.g. contain the same VA or TC related information. For example, for SIGWX products valid at 270000 UTC, the WAFCs would issue all of the products at 260700 UTC during normal modes of operation. If operating in backup mode, all of the products would be issued at 260900 UTC.

2.6Noting that contingency periods equate to a very small percentage of the total number of issuances, the WAFSOPSG may wish to agree that the above amendment proposal is sensible to ensure high- and medium-level BUFR and PNG SIGWX products are consistent with regards their content, particularly VA and TC.

2.7The proposed changes would not necessitate an amendment to Annex 3 since Appendix 2paragraph 1.3.1.1 states that “the dissemination of each forecast shall be completed as soon as technically feasible but not later than 11 hours after standard time of observation”. The above proposal would continue to exceed this requirement.

3.Conclusions

3.1In view of the above discussion, the WAFSOPSG is invited to formulate the following draft conclusion:

Conclusion 5/.. – Alignment to the issuance time of WAFS SIGWX forecasts
That, the WAFC Provider States align, in time for the WAFSOPSG/6 Meeting, the issuance time of WAFS SIGWX forecasts:
a)in the BUFR-code form to 17 hours ahead of validity for high- and medium level SIGWX forecasts; and
b)in the PNG chart form to 17 hours ahead of validity for high- and medium-level SIGWX forecasts.
Note 1.—During WAFC backup modes of operation, including the routine backup tests, the WAFC Provider Statesissue all SIGWX products at 15 hours ahead of validity time;
Note 2.—Volcanic ash and tropical cyclone advisory information arriving after these nominal issue times is incorporated into the subsequent set of SIGWX forecasts issued 6 hours later; and
Note 3.—WAFS users will be advised six months before the implementation of this change via the WAFS Change Notice Board:
).

4.ACTION BY THE wafSOPSG

4.1The WAFSOPSG is invited to:

a)note the information contained in this paper; and

b)agree on a draft conclusion for the groups consideration.

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