Sketching Quadratic Graphs

The predicted amount of rain in Clovertown during the month of July is modeled by the function

$$J(t) = 0.02(t - 13)^2 + 0.05,$$

where $t$ represents the $t$th day in July and $J(t)$ is in inches. On which day of the month should Clovertown expect the least amount of rain?