It's no surprise that these itens are a bit useless and should receive a rework.
My suggestion for the thermometer is that upon examining it your caracter will read the world temperature from it. It's not much but knowing if the world is above 80º can tell if your safe from wildfires, or if it's below 0º and things will stop growing.
For the rainometer I know the game has a "world wetness" hidden variable that constantly increases and when it reaches a certain point it rains. My suggestion would be set the values in % and when the world reaches 100% wetness/moisture/humidity it starts raining. This way your caracter can constantly be examining the machine to see the value increasing (i.e. 60% 80% 95% and then know that rain is about to come). This is specially useful for people who likes to take advantage of electrical damage and needs to wait for the rain.