Solution: The total number of possible outcomes for 7 patterns is $4^7$. To count favorable outcomes, choose 3 patterns to show the specific outcome ("extreme heat") in $\binom73$ ways, and the remaining 4 patterns must show one of the other 3 outcomes, giving $3^4$ possibilities. The probability is $\frac\binom73 \cdot 3^44^7 = \frac35 \cdot 8116384 = \frac283516384$. Thus, the final answer is $\boxed\dfrac283516384$. - Appfinity Technologies