In order to clear that rainfall, you will need to wait for the rain event to end. A rain event will end when no rain registers for 8 hours OR no rain registers for 1 hour and pressure rises by .03inhg or more. Once that has happened, you should be able to hit the Clear Today button and clear those readings. If you have any additional questions, please contact AcuRite Customer support at 877-221-1252. Have a great day!