Aladin Python CLI

A command-line interface for retrieving hourly forecasts from the "Aladin" model developed by the Czech Hydrometeorological Institute.

What is this?

Aladin is a weather forecasting system that can predict various weather parameters (temperature, humidity, clouds, precipitation) in the Czech region with surprisingly satisfactory accuracy. In its current mode of operation, it produces forecasts every 6 hours, each comprising 24 prediction points spaced 3 hours apart. This yields prediction horizon of 72 hours.

Recently I caught myself checking the Aladin website (in Czech) way too often. Unfortunately at the time of writing, I found the frontend not to be too user friendly, so I made this one-day project that caters to all my forecasting needs.

The Python 3 package in this repository can bypass Aladin's frontend and download all weather maps directly from the backend as PNG files, which can be processed in various ways (e.g. to produce a slideshow on your desktop).

How to use it?

You can use the package in two ways: as a library, or as a command-line tool.

Library usage

The aladin package provides a single class Aladin that serves as a client for the backend. You can use the following instance methods to retrieve things:

• list_forecasts() returns a list of available forecast IDs (ints),
• list_params() returns a dict of forecasted parameters (ID/str: human-friendly description/str)
• list_ranges(forecast) returns a list of prediction points (str) for a given forecast ID
• retrieve(param, forecast, range, legacy_radar, write_buffer) downloads PNG data for a given triple of (forecasted parameter ID, forecast ID, prediction point) and writes it to write_buffer (which can be a file or any other MemoryIO), the legacy_radar option is a boolean that enables older appearance for the prec and prec24 parameters. If the PNG data is available, the method returns True, otherwise False.

If any of the above methods encounters network or other issues, appropriate errors are raised.

Command-line usage

List all available forecasts:

aladin -l

Download all prediction points of the latest precipitation forecast:

aladin -p prec

The same thing but also for temperature and relative humidity at 2 meters:

aladin -p prec RH2m T2m

Download only 3-, 6- and 9-hour prediction points of the latest precipitation forecast:

aladin -p prec -r 3 6 9

Download all prediction points of a specific precipitation forecast:

# we retrieved "2021072412" earlier using `aladin -l`
aladin -p prec -f 2021072412

Download all prediction points of all available precipitation forecasts:

aladin -p prec -a

Download all prediction points of the latest precipitation forecast and use ffmpeg to concatenate them into a MP4 movie:

aladin -p prec -m

Here's a complete usage string for the command-line tool:

usage: aladin [-h] [-l] [--list-params] [-a] [-m] [--movie-framerate MOVIE_FRAMERATE] [--legacy-radar] [-f FORECAST [FORECAST ...]] [-p PARAM [PARAM ...]] [-r RANGE [RANGE ...]]

Download weather forecasts from the Aladin model

optional arguments:
  -h, --help            show this help message and exit
  -l, --list-forecasts  prints a list of available forecasts
  --list-params         prints a list of available parameters and their descriptions
  -a, --all-forecasts   retrieves all available forecasts
  -m, --movie           uses ffmpeg to generate mp4 movie for each param
  --movie-framerate MOVIE_FRAMERATE
                        frame rate used for movie, equal to 2 by default
  --legacy-radar        uses legacy radar visualization
  -f FORECAST [FORECAST ...], --forecast FORECAST [FORECAST ...]
                        forecasts to retrieve
  -p PARAM [PARAM ...], --param PARAM [PARAM ...]
                        forecasted parameters to retrieve, possible options include: ["T2m", "prec", "v10mmslp", "nebul", "nebulb", "nebulm", "nebulh", "RH2m", "veind", "Tmxmn", "prec24"]
  -r RANGE [RANGE ...], --range RANGE [RANGE ...]
                        forecast range to retrieve (in hours), possible options are increments of 3 from 0 to 72

Copyright

This repository was created on July 24-25, 2021 by Petr Mánek, and is licensed under the MIT license. Note that this project merely represents an alternative means of accessing the Aladin system, which is widely available to the general public. The author makes no claims regarding generated forecasts, maps and other materials, as these may be subject to other terms and conditions. For more information about their licensing, please check the CHMI website.