The 38F chime is for safety, a warning against the possibility of ice on the road. Checking the owner's manual, there seems to not be a way to turn it off. I get a temp reading all winter long on start.
If you have the 12 button OBC, to set the clock chime off, simply press S/R as you are in clock mode, and you will notice the alarm logo turn on or off.
The six button OBC; the manual says the Memo button is for the alarm (toggle on/off), 15 seconds before the hour in order to let you tune in to the hourly news.