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TAF/METAR interpretation


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lhe
lhe
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I've found some problems with how Skydemon interprets TAFs and METARs.

1) In some cases the TAF/METAR symbols next to an airfield on the map shows "M" even though the weather is better than the particular "Good VFR" settings. Example: Assume "Good VFR" minima settings to be OVC/BKN and SCT both 2000 feet, VIS 8000 m. Then the following TAFs/METARs all give an "M" symbol.


ESMX 150230Z 1504/1512 18010KT 9999 -RA BKN035


ESSL 150450Z 18007KT 150V210 9999 RA FEW049 BKN062 06/04 Q1020 REDZ

ESCF 150450Z 18007KT 9999 -RA NSC 07/05 Q1019


It guess that the observed/forecast rain automatically gives "M"? This doesn't seem very useful. I don't consider light rain with VIS 10 km or more and "no significant cloud" to be marginal...



2) It appears that Skydemon ignore change groups in TAFs. E.g. everything after the first BECMG, TEMPO etc. is ignored. I would expect the program to use the given departure time (if any) or the time set in the "Weather" window.



3) TAFs issued by MIL MET offices in Sweden include forecast QFE and QNH figures, e.g.


ESDF 170830Z 1709/1718 25005KT CAVOK QFE 1011 QNH 1018


I certainly don't expect Skydemon to understand such non-standard format, but it would be good if it could be more defensive in interpreting non-standard TAFs. In this case the four-figure QFE value (1011) is taken to be the horizontal visibility. (Both the TAF decode and the weather symbol on the map shows this.) As CAVOK implies at least 10 km visibility, there can't be a separate visibilty figure, so Skydemon should ignore what looks like a visibility figure following "CAVOK" (just as it appears to ignore the "1018" figure).



4) Skydemon doesn't understand the SNOWTAM part of Swedish METARs. E.g. the METAR


ESSA 150450Z 18015KT CAVOK 06/02 Q1020 R88/19//95 NOSIG


gives an error message "Unrecognised part "R88/19//95" included in METAR ". (This is certainly a very minor complaint.)




Tim Dawson
Tim Dawson
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1. You're correct that the weather conditions also affect the weather rating. We review these from time to time and will take note of your feedback.

2. All the change groups are fully depicted in the TAF inspection window. I guess you are referring to the graphical depiction on the map? If so, we do have plans to vary that for departure time in the future.

3. There is only so much work we are prepared to do in accommodating non-standard TAF/METAR formats, but in this case since CAVOK has already appeared you are correct that we should discard the apparent visibility figure.

4. For the time being SkyDemon ignores SNOWTAM.
Martin Bech
Martin Bech
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Hi Tim
To improve safety I suggest implementing decoding of Snowtam. Snowtams are very structual so decoding should not be a problem - look at attached:


Tim Dawson
Tim Dawson
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That is a good suggestion, but rather than digging up a six-year-old thread it really belongs in the Suggestions forum so others can weigh in on it.
Martin Bech
Martin Bech
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Tim Dawson - 12/2/2019 10:32:22 AM
That is a good suggestion, but rather than digging up a six-year-old thread it really belongs in the Suggestions forum so others can weigh in on it.

Done!
Thanks Tim.

Tim Dawson
Tim Dawson
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Many thanks!
GO

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