At the beginning of the week, Seattle will see mild autumn weather: Monday is expected to be sunny and cool, with temperatures around 16–18 °C, while Tuesday will bring similar conditions, though more high clouds will move in from the north. Cloud cover will increase on Wednesday as an atmospheric system shifts south, but temperatures will remain at roughly the same level. The city will then begin warming quickly: on Thursday, strengthening high pressure and offshore airflow will push temperatures up to 19–22 °C, while Friday will see temperatures rise confidently to 21–23 °C — about 10 degrees above the seasonal average for this time of year.
Based on: Seattle weather: Mild weather turns to warm burst later in the week