Enumclaw is what stands on the other side of the lowest pass in the region

The City of Seattle keeps a document that rates every disaster that could happen to it. In the chapter on windstorms, between the Columbus Day storm and the Inauguration Day storm, there is a sentence about a town forty miles away that Seattle has no jurisdiction over and mentions anyway, because it explains something. Stampede Pass, the planners write, is the lowest pass in the region, and the area immediately below it, Enumclaw, routinely sees strong winds as a result.

The rest of this piece is what that sentence leaves out.

How the air gets here

In winter the air east of the Cascades gets cold, and cold air is heavy, and heavy air means high pressure. When a low comes in off the Pacific and sits over Puget Sound, the two sides of the mountains are no longer at the same pressure, and the air on the heavy side wants very badly to be on the light side. Mountains are in the way. So it goes looking for the lowest place to get over, and around here, Seattle's planners write, the lowest place is Stampede.

The University of Washington's Cliff Mass, who has written about this for decades, describes the rest: the cold air pushes preferentially through the gap, then accelerates down the western slopes and strikes Enumclaw and the communities beside it. On a big day there is a second effect, which he calls mountain-wave amplification: a reversal of the wind above the crest or a layer of stable air there, either of which turns a strong wind into a violent one. The pressure difference on such a day can exceed ten millibars from one side of the range to the other. The highest Mass says he has seen was seventeen.

The affected swath, by his account, is about fifteen miles wide and reaches toward Puget Sound. Seattle's planners note the odd result: Fife and Federal Way can be taking winds of 50 to 60 miles an hour while Seattle itself is nearly calm. Winds of 50 to 70 knots, Mass writes, occur in this area every year. The worst ones can exceed a hundred.

Christmas Eve, 1983

Every account of the east wind this site read arrives at the same date. On December 24, 1983, the cross-Cascade pressure difference reached 17.1 millibars, and the wind that came through the gap, in Mass's words, gusted to over 120 miles an hour in Enumclaw. Roofs came off hundreds of buildings. A Snoqualmie weather writer who went back through the record found spotters reporting gusts past 120 with sustained winds of 75 for more than eighteen hours, mobile homes rolled several hundred feet, and a high-tension power tower down. A 1998 study of Cascade windstorms by Brian Colle and Mass, citing an earlier paper by Mass and Albright, called that storm perhaps the strongest to strike western Washington in the twentieth century.

It should not be confused with the Thanksgiving Day storm a month earlier, which left 75,000 people without power in King County and is listed by Seattle as a regional storm. Christmas Eve was the other thing, the thing that belongs to the gap.

The ones since

The list is only the storms that made the news:

February 12, 1995: gusts of roughly 78 to 89 miles an hour on the slopes around Enumclaw, the event Colle and Mass built their study on, with roofs damaged, trees uprooted and lines down.

One December in John Wise's years as mayor: winds topped out at 80 miles an hour in Enumclaw and Buckley, at least 400 homes in the city lost roofing, and Wise declared a state of emergency by ten in the morning, with the fire station as command post and King County engines sent in. The Courier-Herald's report survives; the year does not, lost in a website migration that dates the story April 30, 2009.

December 20, 2008: a gradient of nearly sixteen millibars by Mass's reckoning, and a commenter on his blog that night relaying a KING 5 report of a 75 mile an hour gust in Enumclaw, while another said parents who remembered 1983 were calling it just like that.

December 17 and 18, 2010: gusts of 70 to 80 at Enumclaw and Black Diamond, a band of 50 to 60 reaching west across south King County, about 100,000 customers without power. Mass rated it a two to five year event.

November 11, 2014: 60 mile an hour gusts, a tree across SR 169 between 424th and 416th that took the power lines with it, downtown dark from nine until twenty past eleven, and Puget Sound Energy saying by mid evening it had restored more than 70,000 customers while the wind kept knocking more out and was at times too dangerous for crews to work.

February 12 and 13, 2021: sustained winds near 40 with gusts near 50, ordinary by the standards above, stripped siding and shingles from new houses at Suntop Farms. Residents later won an arbitration award of $2.3 million against the builder, LGI Homes, and its subcontractor.

November 19, 2024, the bomb cyclone: 74 miles an hour on the plateau against 50 to 60 elsewhere in the county, the highest reading for any community in the state, by Wikipedia's count. Lines and trees started coming down around three in the afternoon. This time it was transmission lines, not just the wires on your street, and PSE told the 98022 ZIP code to expect power back by noon Saturday. Eleven crews came to the Enumclaw area. Trees came down on houses and across parking lot entrances, a downed line caught fire, the Rockridge Country Market lost thousands of dollars of stock, and the fire department's deputy chief, Ben Hayman, told the paper he could not recall a single injury.

Five a year

The Colle and Mass study put numbers on the routine. About five minor windstorms a year, with winds of 34 to 56 miles an hour, arrive downwind of Stampede Gap. Strong events, above 67, come annually or less. Every dated storm in the list above falls between November and February, and so does every wind advisory the National Weather Service has issued for Enumclaw that this site could find, including one this past November for southeast winds of 20 to 30 with gusts to 45, listing Enumclaw with North Bend, Maple Valley, Lea Hill and a dozen other foothill and lowland places.

Living here means that roughly once a winter, and some winters more, the air on the far side of the mountains is going to run out of patience.

What it costs

Roofs, first and always; 1983 took hundreds, the Wise-era storm at least four hundred, and 2021 proved that a 50 mile an hour gust is enough if the shingles were put on badly. Power, second: the three storms with published counts ended with tens of thousands of PSE customers dark, and 2024 showed what happens when the big lines go rather than the small ones. Roads, third: SR 169 north of town lost a tree and its power lines in 2014 and closed for days in 2024, and 410 to Greenwater closed for a morning this March after about thirty trees came down overnight.

The city's only documented response in the record is the Wise emergency declaration and a plan to recoup costs from FEMA. PSE, a year after the bomb cyclone, said it was very confident in an improved response if another one came. This site could not find anything either has published aimed at the gap wind in particular, for a hazard the region's largest city puts in its planning documents by name.

The name

There is a theory, recorded on Wikipedia and nowhere authoritative, that the mountain six miles north of town got its name either from an evil incident there or from the powerful east windstorms that affect the region. The city itself says the name means thundering noise. This site's piece on the town's name takes up the two usual versions; the wind theory is Wikipedia's and no stronger than the others, but it is the one a resident in December would vote for.

The number on the chart

The consolation of the east wind is that it is the one kind of weather in King County you can see coming from Yakima. The pressure builds on the far side of the range a day or two before it comes over, and the number that matters is printed on every surface chart: the difference between the two sides. Ten millibars is a bad night. Seventeen is Christmas Eve, 1983.