The wettest day in Sea-Tac Airport's history was October 20, 2003, when an eye-popping 5.02" of rain fell. That was just about the "perfect storm", pardon the pun, because the rain started right around midnight and so the bulk of the storm almost fit perfectly between the midnights on the 20th.
Second place is 3.41" set on Nov. 20, 1959 and third place was quite recent -- 3.29" on Nov. 6. 2006. To get into the top 10, you need to best 2.72".
Amazingly, number 7 and 8 on the list were set a few days apart. 2.95" fell on November 9, 1990, and then another 2.93" fell on the 24th (the infamous "sink the I-90 bridge" Thanksgiving storm) November 1990 was one of our wettest months ever, but was blown out of the water by the November in 2006 when we had over 15" of rain.
Anyway, with the current storm, we're not expecting to get anywhere near there -- maybe 1.50-2.00" for a storm total for Seattle, and with most of the rain expected to fall overnight Thursday, the midnight cutoff will split this storm's totals across two days.
So let's see those 48 hour rainfall records -- well, that Oct. 20 storm skewed that one too. The overall record is 5.24" set Oct. 20 and 21 in 2003. That's sort of like how Pete Rose and his son Pete Rose Jr. are among the top baseball father-son combinations in combined career hits at 4,258 -- Pete Rose had 4,256, and his son had 2.
Second place for 48 hour rain is 4.43" set in 1951, followed by 4.10" in April 1991 and 3.98" in October 1981.
Incidentally, if you're wondering, that record storm in 2003 also is the record for 24 hour rain over any period of time. The November record is 3.58" set November 23-24, 1990.
How about shorter bursts of rain? I've only got this data up through 1997, so I'm not 100% sure any of these haven't been broken since (especially 2003, and also the storm that had an incredible rain squall that hit Seattle on Dec. 14, 2006 right before the big winds arrived.)
But as of 1997, the record for 5 minute rain is 0.18" and 10 minute rain is 0.20", both set Aug. 9, 1991. (So, likely a thunderstorm and not these pineapple express heavy rain events.) November record is 0.08" and 0.16" respectively. Half hour is 0.35" overall (6/22/93) and 0.30" in November (1990). One hour: 0.54" (Sept. 1979) or 0.47" for November (1990).
Incidentally, you can track where we are by this new rainfall page I just set up.
Stay dry out there!