As colder air poured into the region behind last Monday’s windstorm, there was speculation that a strong Puget Sound Convergence Zone could form over the Everett area and head south, whitening cities along the way with several inches of snow before drifting off into the Cascades. Such a scenario, of course, never materialized—with just light snow showers affecting the region later that night.
22 years ago, it was a much different story.
Tuesday, Dec. 18, 1990, began on a relatively calm note in Seattle, with temperatures at the stroke of midnight resting in the low- to mid-40s under overcast skies. To the north, however, there was trouble brewing—with arctic air from Canada slowly sinking toward the Washington border.
As night turned to morning, the cold air began spilling into the state, dropping the temperature around Puget Sound into the upper 30s. Then, right around lunchtime, a powerful—and unpredicted—Puget Sound Convergence Zone formed near Lynnwood, and all hell broke loose.
Heavy, wet snow fell in droves as the Convergence Zone roared south into Seattle in the early afternoon, blanketing freeways and blinding motorists. Accompanied by howling northerly winds, the Zone peaked in intensity right over downtown—dumping a foot of snow in the heart of the city. As if that weren’t enough, lightning flashed overhead as peals of thunder boomed from the sky—treating stunned Seattleites to a spectacular display of thundersnow. (Thundersnow—thunder, lightning and snow, all rolled into one—also hit the region on Mar. 7, 2002 and Dec. 18, 2008, courtesy of the Convergence Zone.)
The Zone also spread its wrath to the other side of Lake Washington, dropping up to 14 inches of snow in places like Bellevue, Kirkland and Redmond as the afternoon wore on. The heavy snow caught the entire region off guard—so much so that over a thousand children in the area, trapped at school when the storm hit, were forced to spend the night in their classrooms.
Eventually, the Zone began fizzling as it meandered south of Renton, bringing only 2.5 inches of snow to Sea-Tac Airport. In the wake of the blizzard, however, the mercury plummeted as cold Canadian air settled in. By 11 p.m., the temperature at Sea-Tac stood at 21 degrees, with bitter north winds gusting to 43 mph. In Bellingham, it was even worse, with a 16-degree temperature and winds blasting above 60 mph.
The biting cold would go on to grip the region for days, with Sea-Tac staying below freezing until Christmas Day, when the temperature mercifully rose to 36 degrees—only to drop back into the 20s once more near the end of the month. Needless to say, the plethora of snow that buried the area on the 18th remained on the ground for more than a week—cementing the December 1990 Convergence Zone’s place in Seattle lore.
And making it the gold standard by which all future epic snowfalls are judged—the mother of all Puget Sound Convergence Zones.