The Thanksgiving deluge of 1990: Record floods and a sinking I-90 Bridge

It was 40 years ago a big snowstorm and following arctic blast on Thanksgiving weekend that cemented holiday memories for a lifetime.

But 35 years ago, it was a huge rain and wind storm that made waves — literally — that led to record flooding in the mountains and the sinking of the old I-90 Bridge across Lake Washington.

The powerful, multi-day atmospheric river storm arrived on Wednesday just as everyone was heading out on their Thanksgiving travels.

Seared into my memory were my parents flying in that day and then trying to get to pick me up at UW, then take us to other family in Port Angeles for Thanksgiving. Normally about a 2.5-3 hour drive, Seattle traffic was gridlocked for hours during the soggy evening commute with multiple crashes on freeways. It took 7 hours to get there.

Over a foot of rain in just days

But the rains kept falling through the weekend, triggering mudslides and other travel headaches. Up in the Cascades, relentless rains coming on top of another heavy rain event just two weeks triggered massive and widespread flooding.

Some mountain areas saw 1.5-2.5 inches of rain in 6 hours, and 4-8 inches of rain in 24 hours. Multi-day storm totals topped 12-16 inches.

The Snoqualmie River set what was then a record crest in Carnation at 60.70 feet (since topped by storms in 2006 and 2009).  The Skagit River’s record crest at Mount Vernon that week of 37.37 feet still stands today.

Other rivers that broke records in November 1990 include:

• North Fork Stillaguamish at Arlington (Now in 3rd place (2010, 2023))
• Snohomish at Monroe (Still stands)
• Skykomish at Gold Bar (now in 2nd (2006))
• Cedar River at Renton (Still stands)

Two people died in the storm — one man died the he drove around two barriers and attempted to cross a flooded road; a second killed while kayaking in the Green River, which was experiencing 10 times normal river flow, according to the National Weather Service.

Some 450 cattle died as farm lands became inundated. Over 2,000 people were evacuated, including all of Ebey Island near Everett, and at one point, most of the town of Snoqualmie, where the namesake river temporarily reclaimed its flood plain.

Along the Snohomish River, the National Weather Service is credited with issuing a special flood warning urging evacuations when models indicated levees were in danger of failing. “They were able to evacuate persons in the forecast area that if they had not been evacuated would have later been trapped and possibly have lost their lives,” the NWS said in its recap of the storm.

There goes the bridge…

For Seattle, the peak of the rain came on Saturday when 2.93 inches fell in the city — what was at the time, the 5th wettest day on record at Sea-Tac. (Ironically, 4th place was hit just two weeks’ prior at 2.95 inches.  The 2.93 inches sits in 12th place today.)

Holiday traffic was already struggling with the heavy rains, overwhelmed storm rains and road closures due to flooding. It got worse on Sunday when pontoons left open on the old I-90 Bridge during renovation work became filled with the waters from heavy rains and a very stormy Lake Washington.

Engineers discovered this fact on Saturday when the bridge was straining under the weight of the water and tried to start pumping out the pontoons, but it was too late. On Sunday, the bridge began to sink in spectacular fashion.

Luckily, that bridge was no longer used for traffic, having shifted to the new adjacent I-90 bridge, so no one was in peril. But the sinking bridge did do damage to some of the anchors of the new bridge, forcing the closure of I-90 on the super busy Sunday travel day.

Overall damage from the storm was estimated at $100 million, including 42 homes destroyed, and another 1,400 with varying levels of damage.