Will it Happen Again? When the Mother of All Gap Windstorms Hit the Cascade Foothills

The year was 1983.  Michael Jackon's “Billie Jean” hit #1 on the Billboard 100 while movie hits like “Scarface” and “Return of the Jedi” were rolling out of the box office.  And on Christmas Eve of that year, “A Christmas Story” was not yet in marathon-mode on TBS, but actually in theatres near you!  However, for people living in the Cascade foothill communities that day the atmosphere was not so jolly. The mother of all gap windstorms was striking with hurricane-like force!  Renowned meteorologist and University of Washington Atmospheric Sciences professor Cliff Mass has called it, “probably the greatest downslope windstorm of the past century in the Pacific Northwest”.

In the city of Enumclaw, which by the way is a name derived from a Salish term that translates as "place of evil spirits", several spotters reported peak wind gusts exceeding 120 mph with sustained winds of 75 mph for over 18 hours. Yikes!

Enumclaw’s location is considered by several meteorologists to be the Cascade’s epicenter for gap windstorms; this is because of its downslope proximity to Stampede Pass, a relatively low and wide gap, or area of weakness where air movement is channeled through and accelerated in the Cascade mountain range, allowing for a rather common wintertime setup of high pressure (colder air) in eastern Washington to rush towards an incoming storm associated with low pressure (warmer air) off the Pacific coast. Other vulnerable gaps nearby include Snoqualmie pass, Steven’s pass and the Columbia Gorge.

In the Cascade foothills we average five or six gap windstorms per year with winds most commonly in the 40-50 mph range, though their occurrence has seemed more frequent in recent years.

The 12/24/1983 storm caused massive property damage in Enumclaw and surrounding areas; reports at the time cited swaths of downed trees, roofing being ripped off, mobile homes rolling several hundred feet, and even a high-tension powerline tower toppled and crumbled under its own weight.

Highly correlated to our southern neighbor, perhaps with slightly lower wind speeds on average, it’s estimated the Snoqualmie/North Bend vicinity experienced wind gusts of 90-100 mph on that day.  Scary stuff! There are some gap windstorms when our area actually appears to exceed wind speeds spotted in Enumclaw.         

I’ve compiled a Top-10 list ranking historical Cascade gap windstorms (as measured from anemometers in the vicinity of Enumclaw or North Bend):

To be clear, this table does not include the classic major windstorms that caused much broader impact to the Puget Sound region, e.g. Hanukkah Eve 2006, Inauguration Day 1993 or Columbus Day 1962.

 I find gap wind data both fascinating and useful in raising awareness of the powerful wind potential our foothills microclimate exhibits.  Several of you probably recall the 2003 gap windstorm very well.  I would love to hear windstorm memories from those that lived in the foothills area back during the biggest gap windstorms, e.g.  ’03, ‘95 or ’83..

Sources:

• The Weather of the Pacific Northwest, Cliff Mass 2008
• Windstorms along the Western Side of the Washington Cascade Mountains. Part II: Characteristics of Past Events and Three-Dimensional Idealized Simulations, Brian A. Colle and Clifford A. Mass, AMS Journals January 1998
• NOAA Storm Event Database
• WeatherFlow data WindAlert Archives