EVERETT, DEC. 12: The worst of the heavy rainfall is over – that is the good news. All that rainfall that fell since Monday, particularly in the mountains, continues to work its way downstream.
Nearly every river from the Canadian border to the Columbia River is or has been well over its banks. In the North Sound, all rivers have crested and are starting to recede. The key issue though it is going to take some time for all the rivers to drop back within their banks, at least through the weekend.
Historic Event?
Some feel this atmospheric river/heavy rainfall event is one for the history books. For perspective, there have been similar flood events earlier this century let alone over history going back into the 1800s. Those recent big floods occurred in early January 2009, early December 2007, and early November 2006. All of these widespread floods involved atmospheric rivers with heavy rainfall amounts and elevated snow levels.
This atmospheric river also produced copious amounts of rain with snow levels up to at least 7000 feet. In the Cascades from Mt. Baker to White Pass, rain totals ranged from 9 to 15.5 inches.
Much of that rain water rolled straight into rivers and streams. Most North Sound rivers soared to near record levels. Yet two rivers did set new records. The Skagit River at Mt. Vernon crested at 37.7 feet just after midnight Friday, nipping the previous record of 37.4 feet.
The Snohomish River at Snohomish also established a new record flood level reaching 34.15 feet near 530 PM Thursday, breaking the previous record of 33.5 feet.
How Much Rain Fell
Again, the Cascades and Olympics got the brunt of the heavy rainfall. In Western Washington, Seattle-Tacoma International Airport (SEA) received 3.44 inches from Monday through Thursday. Olympia got 5.12 inches during that same time period, and Bellingham 3.38 inches. Along the coast, Hoquiam recorded 5.35 inches of rain while Forks measured 5.84 inches.
During much of this soggy event though, the Olympic rain shadow played a role for parts of the North Sound. As an example, Everett – Paine Field received just 1.37 inches during those 4 days, and the Doppler weather radar clearly showed the absence of rain to the lee (east) side of the Olympic Mountains at times.
More Precautions
It is going to take time for the rivers to recede back into their banks. Evacuations of low-lying areas continue until further notice. Local authorities will give the ‘all clear’ to return to homes and businesses when it becomes safe to do so.
In the meantime, continue to avoid driving around high water – road closed signs. Remember – turn around, don’t drown. Driving on water covered roadways is the leading cause of flood related fatalities. These precautions are all about safety of life.
Landslide Threat
The threat of more landslides will linger through the coming weekend. Soils in the upper layers are soaked and heavy. On steep slopes, those unstable soils could slide. Be wary of the potential of additional landslides.
Another Warm Wet Storm
Unfortunately, the warm wet weather is not quite over yet. After a dry day with some sunshine Saturday, a weak weather system will spawn some showers on Sunday.
Right on that system’s heels though is another wetter weather system that will spread rain onshore Monday. This system also has some warm moist sub-tropical moisture embedded within it for another dose of heavier rainfall with high snow levels. Fortunately, this system will be more short-lived and produce less rain.
Expected rain amounts in the Olympics and Cascades Monday and Tuesday will range from 4 to 7 inches. The coast is forecast to receive another 2 to 4 and half inches, and the interior of Western Washington, a range of 1 to 2 and half inches of rain.
Nevertheless, more rainfall will keep river levels high with the potential for additional flooding. This situation bears watching. The extra rainfall will also maintain the threat of more landslides.
Some Good News!
This warm wet weather system’s associated cold front is forecast to swing onshore by late Tuesday, bringing much needed cooler air dropping snow levels down to below the passes. Showers Wednesday and rest of next week are anticipated in the Western Washington lowlands with more seasonable high temperatures mainly in the 40s. But in the mountains, the showers will fall in the form of snow.
The recent rain has also helped fill thirsty area reservoirs such as Ross Lake on the Skagit River, and the upper Yakima River lakes following a very dry year.
