Blind spot monitor error?
 

2013 ML 350, has blind spot monitor system and park assist. In a slight rain today the system went out. The yellow triangle was flashing at 50 mph, the warning sounds came on for blind spot indication. No red warning light in the mirror however, reset the system and was okay for a few miles. Then the warning on the dash indicated that blind spot monitor was disable, please reffer to owners manuel.

Does the rain sometimes affect the sensor? I am going to wait for a dry day and see if that clears the problem. Just wondering if it is something I need to call the dealership about.

Yes, absolutely call the dealership. Rain should never be detrimental to the functions of your vehicle. It's especially important because this could be considered a safety issue.