AvXML - Version 1.0, Release Candidate 1. Weather Types.

OPMET reports use table 4678 from WMO No 306 (Manual on Codes) to record the type of weather that is observed or forecast.

More detail on the use of code-table 4678 to support IWXXM/METCE can be found here.

Table 4678 provides lists of weather descriptions and the combinations of symbols that represent them. It also provides "rules" on how these should be combined. Three options were considered in preparing AvXML 1.0 RC 1.
1) Do not validate the weather being reported - this is the simplest to implement
2) Validate the reports using algorithms ("business rules") - this was rejected because the rules would be very complex to write, and time consuming to run.
3) Provide a list of permitted entries as a code table - entries would be validated against this list.

Option 3 is preferred by TT-AvXML, but it requires an authoritative list of permitted combinations.

Further information about the use of Table 4678 is available.

A spreadsheet is attached to this page that lists four possible sources of the "authoritative list".

Column 1 (Apply 4678 "rules") attempts to list all the possible combinations from table 4678. Forecasters have pointed out that the list contains entries that mix precipitation from layer cloud and from convective cloud that should be excluded on meteorological grounds. This list also only permits two types of precipitation to be reported in a group - forecasters have commented that reports sometimes contain three types of precipitation.
Column 2 is a list of combinations that a group of aviation forecasters thought are used in practice.
Column 3 is the list that appears in the "METAR/SPECI template" in Annex 3
Column 4 is the list that appears in the "TREND template" in Annex 3.

Request for comments

All comments and contributions will be public. Moderated comments will be collected on our Google Group: CBS-TT-AvXML.

Please prefix the subject line for all comments with [1.0RC1-feedback].

Comments are sought on:
1) whether it is appropriate to produce a list of weather types against which messages would be validated, or whether it is preferable to allow any combination of characters to be reported.

2) which column of the spreadsheet should be used as the basis of setting the authoritative list of weather types, and any additions or deletions that would be needed - bearing in mind that only those combinations in the list would be permitted in valid XML representations of OPMET reports.

3) proposals for inclusion of additional weather types or removal of (incorrect) weather types currently listed

4) proposals for the subset of weather types that may be used for reporting:

• recent weather at an aerodrome (METAR/SPECI)
• present weather at an aerodrome (METAR/SPECI)
• forecast weather at an aerodrome (METAR/SPECI trend forecast and TAF)