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Decoding METARS

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beeman
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Decoding METARS

Postby beeman » Sat Jan 22, 2011 2:11 pm

Hi all,
I look at my local airport METARS to compare the readings I get from my weather station. Today I've seen a code WHT which I've never seen before. I've done a search and can't find what it means.

Can anyone help?

METAR EGUB 220750Z 15001KT 4500 PL SCT020 OVC030 M01/M01 Q1038 GRN BECMG 6000 BR WHT
METAR EGUB 221050Z 00000KT 6000 BR BKN018 BKN030 01/01 Q1038 WHT TEMPO 4000 -RA BKN012 GRN
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steve
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Re: Decoding METARS

Postby steve » Sat Jan 22, 2011 2:29 pm

It's the 'fitness' of the airfield. See 'my' Weatherfaqs site: http://weatherfaqs.org.uk/node/197

Colour states: METAR reports from military airfields operated by the RAF, some USAF and others may have a 'colour-code' appended (usually only when ATC is open), which describes the airfield 'fitness': these run from BLU best, through WHT GRN YLO (1 and 2), AMB and RED. The colour is based on the lowest cloud base (usually 3 oktas or more cover, but some use 5 oktas) and the horizontal 'MET' visibility. BLACK is also used, for airfield closed for non-weather reasons.
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Please read the posts in the Announcements section about the current status of Cumulus development since I have retired from my day job

beeman
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Re: Decoding METARS

Postby beeman » Sat Jan 22, 2011 2:35 pm

Great, thanks Steve and thanks for the link. Why didn't I find that with my searching?????
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gemini06720
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Re: Decoding METARS

Postby gemini06720 » Sat Jan 22, 2011 2:55 pm

You could also check the METAR page on Wikipedia... ;)

beeman
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Re: Decoding METARS

Postby beeman » Sat Jan 22, 2011 3:36 pm

gemini06720 wrote:You could also check the METAR page on Wikipedia... ;)


Hi Ray, that was the second place I looked but even looking again I can't find WHT. Maybe I should get some new glasses :lol:
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GraemeT
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Re: Decoding METARS

Postby GraemeT » Sun Jan 23, 2011 1:18 am

Cheers,
Graeme.

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beeman
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Re: Decoding METARS

Postby beeman » Fri Jan 28, 2011 10:25 pm

Thanks Graeme I also found this http://metaf2xml.sourceforge.net/gui.html
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GraemeT
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Re: Decoding METARS

Postby GraemeT » Thu Feb 03, 2011 9:35 pm

For anyone who's interested, here is my php script, a bit rough in places, to make some use of metars for display on a webpage.
It is called by a vbs script, run as a windoze task and takes input from a textfile created by mweather.exe, also called by the same vbs script.
The output is written to the currentconditions.txt file for Cumulus to use.

http://weather.gktnet.com/public/weather/metar_scripts.zip

Cheers,
Cheers,
Graeme.

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uncle_bob
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Re: Decoding METARS

Postby uncle_bob » Mon Oct 17, 2011 8:50 am

Hi Graeme, thanks for this.
Any chance though, of a readme or something with instructions for usage?
Cheers Bob

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nking
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Re: Decoding METARS

Postby nking » Mon Oct 17, 2011 1:55 pm

uncle_bob wrote:Hi Graeme, thanks for this.
Any chance though, of a readme or something with instructions for usage?
Cheers Bob


Hi Bob,

Would you like to see if the attached works OK for you
You do not have the required permissions to view the files attached to this post.

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GraemeT
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Re: Decoding METARS

Postby GraemeT » Tue Oct 18, 2011 2:37 am

Bob,
Neil's doco pretty much sums it up. He's tackled it in a somewhat less complex way than I did.
My .php and .vbs scripts just give flexibility in the sense that you only need to download the Metar data every 30 mins or so.
They were originally intended to perform a few more functions, but to date, I haven't gotten around to adding the code (by the time I do, Cumulus might be up to version 8 or so :roll: ).
Cheers,
Graeme.

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gemini06720
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Re: Decoding METARS

Postby gemini06720 » Wed Oct 19, 2011 2:45 pm

For the past days, I have been working on a old PHP script ... the rewritten updated version of the script can now download the METAR data from NOAA, save that data into a cache directory, read the data from the cache directory and create (and save) a 'currentconditions.txt' type file.

It is not quite ready for distribution - lots of debugging code still left in there as there are still a few more bugs to quash...

...

Unfortunately, because of the use of old functions, the script stopped working when I upgraded PHP on my server :( and too many changes would be required to make the script useful.
Last edited by gemini06720 on Thu Jan 10, 2013 3:32 pm, edited 2 times in total.

uncle_bob
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Re: Decoding METARS

Postby uncle_bob » Sun Oct 23, 2011 1:34 am

Ok I got it working, thanks! Had to wrap it a bat file per this thread.
viewtopic.php?f=14&t=6138

I'm actually thinking it may be better to scrape the google weather api for more info.
I think I'll start a thread regarding this topic, and post back the link to it.
Edit: New thread here viewtopic.php?f=14&t=6172

Cheers Bob

lee4019
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Re: Decoding METARS

Postby lee4019 » Thu Jan 10, 2013 12:31 pm

Thanks

I'm going to try these and see if I can it to work.

sfws
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Re: Decoding METARS

Postby sfws » Fri Sep 29, 2017 8:19 am

Re-opening this old topic to mention some METAR changes in 2017.

The International Civil Aviation Organization do not seem to have changed their guidance Annex 3 to the Convention on International Civil Aviation, the latest 16th edition was published July 2007 and effective 7 November 2007. [EDIT - removed repeated phase].

World Meteorological Office specification for METAR is in WMO Document No. 306, Manual on Codes, Volume 1, Part A; current form code FM 15–XIV - the Roman numeral XIV identifies the session of CSM (Commission for Synoptic Meteorology) or of CBS (Commission for Basic Systems) which made the latest amendment and this indicates that latest update has changed several times from the FM 15-IX that is indirectly referenced by this thread. I have not purchased any WMO document (WMO sell them, they do not make them available for free viewing on-line) but you can look up on-line reports from the various sessions. I have not worked through those (because I got confused by those I did look at), but have gained an impression that WMO are trying to tighten the specification to make METAR more consistent internationally for example by standardising on units used for wind speed and cloud height and removing a few seldom used formats (WMO have withdrawn the 'VVVNDV' format (as of June 2011)).

EDIT - ICAO/WMO in 2016 announced (http://www.ofcm.gov/groups/iwxxm/meetin ... status.pdf) that the METAR format of traditional alphanumerical characters (TAC) would be replaced by a new international XML style version mandatory from ICAO Standards and Recommended Practices - Annex 3 Amendment 78 (November 2020). The new format IWXXM is being developed by WMO and ICAO.
IWXXM Messages will be exchanged over Aeronautical Message Handling System (AMHS) as the Aeronautical Fixed Telecommunications Network (AFTN) can't accept them.


The UK Civil Aviation Authority defines content of METAR in chapter 4 in 'CAP 746: Requirements for Meteorological Observations at Aerodromes', they published version 4 of that guidance in March 2017. The changes from 2003, 2012, and 2014 versions are listed on pages 9-11 of the document (too many to list here since the previous post in this topic) and it can be downloaded freely from "http://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=11&mode=detail&id=1110".

The US standard for aviation surface observations is in Federal Meteorological Handbook No. 1 (FCM-H1-2017), that is a new edition just published that will be effective 30 November 2017 found at "http://www.ofcm.gov/publications/fmh/FMH1/FMH1_2017.pdf". Again the changes from the September 2005 edition are listed in it, they relate to snow pellets, hail, present weather, intensity modifiers for precipitation, and ice accretion.

Current raw METAR (excluding NIL reports) can still be read from '//tgftp.nws.noaa.gov/data/observations/metar/stations/????.TXT' (where ???? is replaced by the relevant ICAO identifier) using either CURL, file socket reads, or FTP. Any METAR back to 1 January 2005 can be downloaded from a storage database at http://www.ogimet.com/metars.phtml.en (with an option to output in text format) and viewed on a web page on that site.

Steve Loft published (back in January 2008) a guide to METAR content at http://weatherfaqs.org.uk/node/197. There are a number of decoders still available online, they vary in how much of a METAR they actually turn into plain English, most focus on the mandatory groups and ignore the least used ones. Several Cumulus-using web sites already include Ken True's script available at "http://saratoga-weather.org/scripts.php" rather than the Nirsoft programme mentioned in this topic, there you can either download a stand-alone zip that contains scripts for reading METAR, for decoding them, and for a web page that displays them or you can download his whole package that displays information from many sources (more information in Saratoga Templates part of forum).

If anyone is interested, I have written in PHP 7 a METAR decoding script that takes into account all the 2017 changes listed above. Although initially based on the guidance in the 'CAP 746' document, because I use it for decoding UK METAR, I have extended it using (FCM-H1-2017) to work for our USAF stations too (it decodes 26 of the 41 possible codes appearing in the USA use of the remarks group) and it even decodes content in the METAR optional groups that obeys the guidance from ICAO and others found on-line. I have included my own text for the additional Colour State pseudo Group added to METAR Present Weather and Trend Groups by RAF in UK and military airfields in Holland with certain METAR issues. [EDIT - corrected spelling errors in this paragraph].

Although I believe my script will work in other environments, it was written to run on my PC's web server (from Uniform) in conjunction with other scripts that I have on my server, my decoder script does not include any language translation options, it simply takes in a raw METAR string (a separate script is needed to read the METAR from the sources I mention), and populates a number of arrays (a separate script is needed to take information out of the arrays and produce a web page). I cannot commit to support, so you need some expertise in PHP to do any tailoring you want. My script is well commented, it has optional diagnostic output to show what it is doing as it decodes a METAR and it will output the whole METAR to a text file if it finds it cannot decode part of the content. I have used this last feature to rewrite my code to cope with more extensive METAR decoding (unfortunately some aerodrome observers do make coding mistakes sometimes).
Last edited by sfws on Thu Nov 23, 2017 10:20 am, edited 3 times in total.


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