Wrong weather data for Lyon (France)

[xlucas]

Hello,

Weather forecast for Thursday 27 of April sounds really off for the city of Lyon, France.

➜  ~ curl http://wttr.in/Lyon
Weather report: Lyon, France

  _`/"".-.     Rain, Rain Shower
   ,\_(   ).   10-11 °C
    /(___(__)  ↖ 9 km/h
      ‘ ‘ ‘ ‘  6 km
     ‘ ‘ ‘ ‘   0.7 mm
                                                       ┌─────────────┐
┌──────────────────────────────┬───────────────────────┤  Tue 25 Apr ├───────────────────────┬──────────────────────────────┐
│            Morning           │             Noon      └──────┬──────┘     Evening           │             Night            │
├──────────────────────────────┼──────────────────────────────┼──────────────────────────────┼──────────────────────────────┤
│  _`/"".-.     Light rain sho…│  _`/"".-.     Light rain sho…│      .-.      Patchy light r…│      .-.      Light rain     │
│   ,\_(   ).   13-14 °C       │   ,\_(   ).   14-15 °C       │     (   ).    14 °C          │     (   ).    11-12 °C       │
│    /(___(__)  ↑ 18-22 km/h   │    /(___(__)  ↑ 15 km/h      │    (___(__)   ↘ 15-21 km/h   │    (___(__)   ↘ 18-26 km/h   │
│      ‘ ‘ ‘ ‘  19 km          │      ‘ ‘ ‘ ‘  17 km          │     ‘ ‘ ‘ ‘   13 km          │     ‘ ‘ ‘ ‘   11 km          │
│     ‘ ‘ ‘ ‘   0.8 mm | 61%   │     ‘ ‘ ‘ ‘   0.8 mm | 89%   │    ‘ ‘ ‘ ‘    3.0 mm | 100%  │    ‘ ‘ ‘ ‘    2.0 mm | 100%  │
└──────────────────────────────┴──────────────────────────────┴──────────────────────────────┴──────────────────────────────┘
                                                       ┌─────────────┐
┌──────────────────────────────┬───────────────────────┤  Wed 26 Apr ├───────────────────────┬──────────────────────────────┐
│            Morning           │             Noon      └──────┬──────┘     Evening           │             Night            │
├──────────────────────────────┼──────────────────────────────┼──────────────────────────────┼──────────────────────────────┤
│  _`/"".-.     Patchy rain po…│    \  /       Partly cloudy  │  _`/"".-.     Light rain sho…│  _`/"".-.     Patchy rain po…│
│   ,\_(   ).   4-6 °C         │  _ /"".-.     7 °C           │   ,\_(   ).   11 °C          │   ,\_(   ).   8 °C           │
│    /(___(__)  ↘ 10-21 km/h   │    \_(   ).   ↓ 16-23 km/h   │    /(___(__)  ↘ 16-23 km/h   │    /(___(__)  ↘ 12-21 km/h   │
│      ‘ ‘ ‘ ‘  16 km          │    /(___(__)  16 km          │      ‘ ‘ ‘ ‘  15 km          │      ‘ ‘ ‘ ‘  14 km          │
│     ‘ ‘ ‘ ‘   0.0 mm | 21%   │               0.1 mm | 68%   │     ‘ ‘ ‘ ‘   0.2 mm | 83%   │     ‘ ‘ ‘ ‘   0.1 mm | 47%   │
└──────────────────────────────┴──────────────────────────────┴──────────────────────────────┴──────────────────────────────┘
                                                       ┌─────────────┐
┌──────────────────────────────┬───────────────────────┤  Thu 27 Apr ├───────────────────────┬──────────────────────────────┐
│            Morning           │             Noon      └──────┬──────┘     Evening           │             Night            │
├──────────────────────────────┼──────────────────────────────┼──────────────────────────────┼──────────────────────────────┤
│  _`/"".-.     Light sleet sh…│      .-.      Heavy snow     │  _`/"".-.     Light rain sho…│  _`/"".-.     Patchy rain po…│
│   ,\_(   ).   4-6 °C         │     (   ).    10 °C          │   ,\_(   ).   11-12 °C       │   ,\_(   ).   7-8 °C         │
│    /(___(__)  ↘ 20 km/h      │    (___(__)   ↘ 22-24 km/h   │    /(___(__)  ↘ 21-26 km/h   │    /(___(__)  ↘ 14-24 km/h   │
│      ‘ * ‘ *  18 km          │    * * * *    16 km          │      ‘ ‘ ‘ ‘  14 km          │      ‘ ‘ ‘ ‘  15 km          │
│     * ‘ * ‘   1.8 mm | 32%   │   * * * *     1.2 mm | 81%   │     ‘ ‘ ‘ ‘   0.6 mm | 89%   │     ‘ ‘ ‘ ‘   0.2 mm | 83%   │
└──────────────────────────────┴──────────────────────────────┴──────────────────────────────┴──────────────────────────────┘

You can see snow prediction for this particular day while it's spring there and weather is getting mild, with temperature records usually above 10 - 15°C at noon.

Local and other popular weather forecast services show no such thing. For instance, the french weather forecast agency shows this : http://www.meteofrance.com/previsions-meteo-france/lyon/69000 (click on 'jeudi 27').

[chubin]

@xlucas: Hi, Lucas!

Thank you for reporting this, but I must note that there were no snow predictions:
(that is the same in French)

Prévisions météo pour: Lyon, France

  _`/"".-.     Averse de pluie modérée
   ,\_(   ).   9-11 °C        
    /(___(__)  ↑ 13 km/h      
    ‚‘‚‘‚‘‚‘   8 km           
    ‚’‚’‚’‚’   0.7 mm         
                                                       ┌─────────────┐                                                       
┌──────────────────────────────┬───────────────────────┤mar. 25 avril├───────────────────────┬──────────────────────────────┐
│             Matin            │          Après-midi   └──────┬──────┘       Soir            │             Nuit             │
├──────────────────────────────┼──────────────────────────────┼──────────────────────────────┼──────────────────────────────┤
│  _`/"".-.     Averse de plui…│  _`/"".-.     Averse de plui…│      .-.      Pluie légère é…│      .-.      Pluie légère   │
│   ,\_(   ).   13-14 °C       │   ,\_(   ).   14-15 °C       │     (   ).    14 °C          │     (   ).    11-12 °C       │
│    /(___(__)  ↑ 18-22 km/h   │    /(___(__)  ↑ 15 km/h      │    (___(__)   ↘ 15-21 km/h   │    (___(__)   ↘ 18-26 km/h   │
│      ‘ ‘ ‘ ‘  19 km          │      ‘ ‘ ‘ ‘  17 km          │     ‘ ‘ ‘ ‘   13 km          │     ‘ ‘ ‘ ‘   11 km          │
│     ‘ ‘ ‘ ‘   0.8 mm | 61%   │     ‘ ‘ ‘ ‘   0.8 mm | 89%   │    ‘ ‘ ‘ ‘    3.0 mm | 100%  │    ‘ ‘ ‘ ‘    2.0 mm | 100%  │
└──────────────────────────────┴──────────────────────────────┴──────────────────────────────┴──────────────────────────────┘
                                                       ┌─────────────┐                                                       
┌──────────────────────────────┬───────────────────────┤mer. 26 avril├───────────────────────┬──────────────────────────────┐
│             Matin            │          Après-midi   └──────┬──────┘       Soir            │             Nuit             │
├──────────────────────────────┼──────────────────────────────┼──────────────────────────────┼──────────────────────────────┤
│  _`/"".-.     Pluie éparse à │    \  /       Partiellement …│  _`/"".-.     Averse de plui…│  _`/"".-.     Pluie éparse à │
│   ,\_(   ).   4-6 °C         │  _ /"".-.     7 °C           │   ,\_(   ).   11 °C          │   ,\_(   ).   8 °C           │
│    /(___(__)  ↘ 10-21 km/h   │    \_(   ).   ↓ 16-23 km/h   │    /(___(__)  ↘ 16-23 km/h   │    /(___(__)  ↘ 12-21 km/h   │
│      ‘ ‘ ‘ ‘  16 km          │    /(___(__)  16 km          │      ‘ ‘ ‘ ‘  15 km          │      ‘ ‘ ‘ ‘  14 km          │
│     ‘ ‘ ‘ ‘   0.0 mm | 21%   │               0.1 mm | 68%   │     ‘ ‘ ‘ ‘   0.2 mm | 83%   │     ‘ ‘ ‘ ‘   0.1 mm | 47%   │
└──────────────────────────────┴──────────────────────────────┴──────────────────────────────┴──────────────────────────────┘
                                                       ┌─────────────┐                                                       
┌──────────────────────────────┬───────────────────────┤jeu. 27 avril├───────────────────────┬──────────────────────────────┐
│             Matin            │          Après-midi   └──────┬──────┘       Soir            │             Nuit             │
├──────────────────────────────┼──────────────────────────────┼──────────────────────────────┼──────────────────────────────┤
│  _`/"".-.     Légères averse…│      .-.      Neige forte    │  _`/"".-.     Averse de plui…│  _`/"".-.     Pluie éparse à │
│   ,\_(   ).   4-6 °C         │     (   ).    10 °C          │   ,\_(   ).   11-12 °C       │   ,\_(   ).   7-8 °C         │
│    /(___(__)  ↘ 20 km/h      │    (___(__)   ↘ 22-24 km/h   │    /(___(__)  ↘ 21-26 km/h   │    /(___(__)  ↘ 14-24 km/h   │
│      ‘ * ‘ *  18 km          │    * * * *    16 km          │      ‘ ‘ ‘ ‘  14 km          │      ‘ ‘ ‘ ‘  15 km          │
│     * ‘ * ‘   1.8 mm | 32%   │   * * * *     1.2 mm | 81%   │     ‘ ‘ ‘ ‘   0.6 mm | 89%   │     ‘ ‘ ‘ ‘   0.2 mm | 83%   │
└──────────────────────────────┴──────────────────────────────┴──────────────────────────────┴──────────────────────────────┘

(if you mean 25 apr). It was shower prediction, not snow prediction.

If you mean 27 apr, there is snow indeed, but why are you sure that it is impossible?
We had snow in Munich two days ago, why it's not possible that it comes again?

And look at this photo:

https://pbs.twimg.com/media/C-CPAjTXYAAC6L9.jpg

This photo I received from one of wttr.in users.
The city on the photo has almost the same latitude as Lyon.

[xlucas]

Hello @chubin

I'm referring to the 27th of April, as mentioned in the beginning of my post.

It sounds really impossible for this time of year, given predicted temperatures for that day and current temperatures, and their evolution for the past few weeks. It could be rain but not snow.

The French weather forecast agency detailed predictions is 0% snow probability and 0% frost probability for the whole week. Basically looks like this other weather forecast service : http://www.accuweather.com/en/en/lyon/171210/hourly-weather-forecast/171210?hour=57.

Also there's no snow predicted anywhere else in the surrounding countryside nor in the whole country for the local weather forecast service at noon.

I can send you a picture on thursday :)

[chubin]

Check this forecast for example:

https://www.worldweatheronline.com/v2/weather.aspx?q=Lyon,%20France

Open Thursday, afternoon

As you can see, in this forecast you also have snow

[chubin]

Yes, but you are right. Our datasource is sometimes really inaccurate. I think the best solution would be to have several datasources and let users choose from

[xlucas]

That would be nice !

[the-n3i]

so how about accessing different countries' official weather services? At least the German weather service offers free FTP access and I'm sure others do that as well. Using a local weather service should give more accurate predictions, right?

[chubin]

@the-n3i It's a good question. I don't know if a local weather service gives more accurate predictions, but it is at least a good idea to have different data sources and combine them (or give a user ability to chose from). What German local weather services are you talking about?

[the-n3i]

I'm talking about "DWD" (Deutscher Wetterdienst, literally "German Weather Service"). It's a state-run service and therefore has to give access to its data under a relatively free license.
Information about DWD in English can be found here.
Info about FTP Access to their data and the restrictions can be found here.

[chubin]

@the-n3i Das ist echt interessant. Ich werde mir das mal genauer ansehen. Vielen Dank für den Hinweis. Ich wusste gar nicht, dass die DWD Daten frei zu Verfügung gestellt werden.

(I better switch back to English because of other users who could read this issue later).
Thank you very much for the link. I'll check the format of the data, and how often they are actualized and other things like that.

[chubin]

see also #9

[pabloab]

All the issues related to inaccurate forecasts are duplicates of issue #9, isn't it?

[chubin]

@pabloab Maybe yes, or maybe not. This also can be caused by #523 or #526

[vestingz]

@the-n3i Das ist echt interessant. Ich werde mir das mal genauer ansehen. Vielen Dank für den Hinweis. Ich wusste gar nicht, dass die DWD Daten frei zu Verfügung gestellt werden.

(I better switch back to English because of other users who could read this issue later).
Thank you very much for the link. I'll check the format of the data, and how often they are actualized and other things like that.

Yes, fortunately DWD has an [Open Data Program](https://www.dwd.de/EN/ourservices/opendata/opendata.html].
It's usage seems to be a bit tedious, so one might be interested in a free and simple JSON interface to that data, which is provided by brightsky.dev. It is also well documented, including examples of working requests through curl.

[chubin]

@vestingz BrightSky looks pretty decent. Thank you for pointing me at it. I will add it to the potential data sources list

[ScanuNicco]

Have you considered adding weather.gov to the list of potential sources? They have a free JSON API with a seemingly high data limit. https://www.weather.gov/documentation/services-web-api

It seems there's a two step process to getting the weather. First a call has to be made to https://api.weather.gov/points/{latitude},{longitude} to determine the responsible weather office and the position of the location on that office's grid. Then a call can be made to https://api.weather.gov/gridpoints/{office}/{grid X},{grid Y}/forecast to get the forecast. The first item under periods seems to contain the current forecast.

[patrick-zippenfenig]

I just came across this ticket while browsing GitHub. I started my own weather API that also offers direct access to DWD, MeteoFrance, NOAA GFS, Yr.no, etc. Depending on the location different weather models are used automatically. I actually made it for open source projects to be used without any API key: https://open-meteo.com

Code is available here: https://github.com/open-meteo/open-meteo