Your plan looks good. Maybe the Indi watchdog driver is able to trigger the observatory shutdown if the connection to the wheater station is lost, but not sure of that.
I a currently using something rather similar to your plan to shutdown my observatory is case of power outage. I use the indi wheater watcher driver in combination with my wheather station s (AAG Cloud whatcher and openwheather map). The principle of this driver is to read a text file where the wheather informations are written and you need to write your own script for that purpose. So, I wrote a script that periodicaly fetch the data from the wheater station a write it to the text file as required. But this same script also checks for the existance of a file named /etc/poweroutage (name it as you like) created by nut when a power outage event is happening (you need to confiure nut for that). If this file exists, the script just write that wheather is in danger zone whitch triggers the observatory shutdown.

Hope this helps.
Sebastien

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