Indeed, looking back over the past 109 years, Nov. 19 is far and away the day it has rained the most -- a whopping 83 times. The second-wettest day is Jan. 13 with only 76 times.
If a dry day is what you need, try late July or early August. On July 22, July 30, Aug. 1, and Aug. 4, it has only rained 9 times in the last 110 years. That's why the big SeaFair events are held during the last week in July and first week in August -- they've done their weather homework.