Oregon Scientific weather stations can be expanded with additional sensors which we have here. You can also use these as replacements should your sensor develop a fault.
Remember that your console may need to 'search' for a replacement or additional sensor before it starts displaying readings.
As with other brands, the temperature and humidity sensors are 'splash proof' so should be kept out of direct rain to prolong their life as per the instructions. Ir you may consider housing them in a TFA sensor shelter to help prolong their life.