To find the current temperature, you need to subtract the change in temperature from the temperature yesterday.
The temperature yesterday was \( 13^\circ C \), and the change in temperature overnight was \( -18.6^\circ C \).
So, the calculation is:
\[ \text{Current temperature} = 13^\circ C + (-18.6^\circ C) = 13^\circ C - 18.6^\circ C = -5.6^\circ C \]
Therefore, the current temperature is \( -5.6^\circ C \).