Seattle averages 41 days of dense fog a year (with visibility of 1/4 mile or less) with (surprise!) October being the foggiest month of the year with an average of 7 days of fog.
The foggiest year was 1954, where we had 65 days of dense fog.
And those of you who were here during the Holidays in 1985 must have wondered if the fog would ever lift, as the 13 days between Dec. 16 and Dec. 28 holds the record of most consecutive days with dense fog.
If you're trying to dodge the fog, stay away from Oct. 16, Dec. 13 and Dec. 16 as those are statistically the foggiest days of the year, each with 16 instances of dense fog over the past 49 years.