Automation to display different photos depending on weather conditions

Configuration
10

Ok, you need to check for lower case state in your template. So “snowy” not “Snowy”.

And you can simplify your template a bit:

template:
  - trigger:
      - platform: state
        entity_id: weather.forecast_home
        to: 
    image:
     - name: Weather Image
       unique_id: 7bbd302d-3246-40ab-aad8-3760d1b75a76
       url: >
         {% if is_state('weather.forecast_home','cloudy') %}
           http://192.168.1.107:8123/local/weather_images/Cloudy.jpg
         {% elif is_state('weather.forecast_home','snowy') %}
           http://192.168.1.107:8123/local/weather_images/Snowy.jpg
         {% elif is_state('weather.forecast_home','sunny') %}
           http://192.168.1.107:8123/local/weather_images/Sunny.jpg
         {% else %}
           http://192.168.1.107:8123/local/weather_images/Unknown.jpg
         {% endif %}

Note the letter case of the file names in the template are capitalised. This must match your file names exactly. Also you need to restart HA after creating the config/www folder if it does not already exist.

Finally, you can add as many elif tests as you need. e.g. you could add this if the state exists:
``

         {% elif is_state('weather.forecast_home','stormy') %}
           http://192.168.1.107:8123/local/weather_images/Stormy.jpg