METAR Reader

A Flask web application that turns cryptic aviation weather reports (METARs) into plain-English descriptions anyone can understand.

Type in any ICAO airport code and get a friendly summary like:

Mostly cloudy. Temperature 13°C (55°F). Wind from the West at 11 knots (13 mph). Excellent visibility.

What is a METAR?

A METAR is a standardized weather observation used by pilots and air traffic control worldwide. They look like this:

KHIO 022353Z 26011KT 10SM BKN060 13/01 A3021

This app decodes every field — wind direction and speed, visibility, cloud layers, temperature, dewpoint, and altimeter setting — and presents them in a format that requires no aviation knowledge to read.

Features

• Live data fetched directly from aviationweather.gov
• Supports any ICAO airport code worldwide (e.g. KLAX, EGLL, RJTT)
• Converts units to mph and °F alongside native aviation units
• Handles complex visibility formats, gusting winds, multiple cloud layers, and present weather (rain, snow, fog, thunderstorms, etc.)
• Collapsible raw METAR display for the curious
• Clean, mobile-friendly interface

Installation

Requirements: Python 3.10 or later

1. Clone the repository

   git clone https://github.com/your-username/metar-reader.git
   cd metar-reader

2. Create and activate a virtual environment (recommended)

   python3 -m venv venv
   source venv/bin/activate      # macOS / Linux
   venv\Scripts\activate         # Windows

3. Install dependencies

   pip install -r requirements.txt

4. Run the application

   python app.py

5. Open your browser and go to http://127.0.0.1:5000

Usage

Enter a four-letter ICAO airport code in the search box and press Get Weather.

Example code	Airport
KLAX	Los Angeles International
KJFK	John F. Kennedy International (New York)
KORD	O'Hare International (Chicago)
EGLL	London Heathrow
RJTT	Tokyo Haneda

Tip: ICAO codes are not the same as the shorter IATA codes used on flight tickets (e.g. LAX, JFK). In the US, most codes start with K followed by the three-letter IATA code.

Testing

The test suite uses pytest and covers all parsing logic and Flask routes. No network connection is required — external API calls are mocked.

Run the tests:

pytest test_app.py -v

Expected output: 72 tests passing in under a second.

The suite is organised into four test classes:

Class	Tests	Covers
TestDegreesToCompass	10	Cardinal and intercardinal wind direction conversions
TestParseVisibility	11	All visibility formats: statute miles, fractions, meters, CAVOK, "less than" prefix
TestDecodeMetar	29	Every METAR field — wind, gusts, sky layers, weather phenomena, temperatures, altimeter, edge cases
TestGenerateSummary	12	Plain-English summaries for all sky and weather conditions
TestFlaskRoutes	8	HTTP responses, mocked API calls, error handling, form behaviour

Data Source

Weather data is retrieved in real time from the Aviation Weather Center API, operated by NOAA. No API key is required.

Project Structure

metar-reader/
├── app.py              # Flask application and METAR parser
├── test_app.py         # Pytest unit and integration tests
├── requirements.txt    # Python dependencies
└── templates/
    └── index.html      # Front-end template

License

MIT