The incoming system carries the same AR-4 rating as the atmospheric river that shattered flood records across the region this week. The Skagit River near Mount Vernon crested at 41.54 feet early Friday, surpassing the previous record of 41.18 feet set in November 1990. The Snohomish River crested at 34.1 feet Thursday, topping its 1990 record of 33.5 feet.<\/p>\n
What is a Pineapple Express?<\/p>\n
You\u2019ve probably heard both terms thrown around this week, sometimes interchangeably. Here\u2019s the difference: an atmospheric river is any long, narrow corridor of moisture that flows through the atmosphere, often stretching thousands of miles from the tropics to the Pacific Northwest. A Pineapple Express is a specific type of atmospheric river that originates near Hawaii.<\/p>\n
\u201cAtmospheric river and Pineapple Express are pretty much interchangeable; it just depends on where the moisture source originates,\u201d Tsaparis explained. \u201cBut tropical moisture reaching the Pacific Northwest is a recipe for disaster, as we\u2019re seeing right now.\u201d<\/p>\n
This week\u2019s storm stretched even farther than Hawaii, pulling moisture from nearly as far as Asia. Next week\u2019s system fits the classic Pineapple Express pattern, drawing warm, wet air directly from the Hawaiian islands.<\/p>\n
Next week\u2019s storm won\u2019t be as severe, but rivers could flood again<\/p>\n
The good news: next week\u2019s Pineapple Express should not match the destruction caused by this week\u2019s event. The key difference is duration.<\/p>\n
\u201cIt won\u2019t be as extreme because, unlike this week, where it was on and off pretty much since Sunday, the rain will be more confined to just a couple of days next week,\u201d Tsaparis said.<\/p>\n
Rainfall totals are expected to reach 5 to 10 inches in the hardest-hit areas, compared to the 15 to 20 inches that fell in parts of the Olympic and Cascade Mountains this week. Still, that is more than enough to cause problems for rivers that have barely begun to recede.<\/p>\n
\u201cThe takeaway message is we could still see those rivers rise again,\u201d Tsaparis said. \u201cIf you\u2019re in a flood-prone region, heed those evacuation orders when they\u2019re given, or even as a precaution, consider getting out before orders are issued.\u201d<\/p>\n
Warm temperatures continue to make flooding worse<\/p>\n
One factor compounding the flood risk: it\u2019s simply too warm. Record temperatures across the western U.S. have meant that precipitation is falling as rain rather than snow, even at higher elevations.<\/p>\n
\u201cThe reason that\u2019s making the rainfall situation worse is that if it were colder, we\u2019d be talking about the foothills and above getting mostly snow,\u201d Tsaparis said. \u201cThat snow would stay locked in, which would be good not just for skiers but also to hold that water until next spring before it flowed downhill.\u201d<\/p>\n
Instead, all that moisture races directly into rivers and streams.<\/p>\n
\u201cIt\u2019s all liquid rain for the most part, with the exception being the far peaks where we\u2019re getting snowfall,\u201d Tsaparis said. \u201cElsewhere, it just races downhill and turns into this historic flooding event.\u201d<\/p>\n
How the atmospheric river scale works<\/p>\n
The AR scale, which rates atmospheric rivers from 1 to 5 based on their intensity and potential impact, is a relatively recent tool. Tsaparis said it has only been in use for the past couple of years, but it helps communicate risk to the public in a way similar to hurricane categories.<\/p>\n
\u201cLevel 4 out of 5 is pretty intense,\u201d he said.<\/p>\n
The scale measures a combination of moisture content, wind speed, and how long the system will affect a given area. This week\u2019s AR-4 caused catastrophic flooding in part because it lingered over the same region for days. Next week\u2019s AR-4, while equally intense on paper, should move through more quickly.<\/p>\n
What to expect this weekend and beyond<\/p>\n
Saturday looks dry across most of western Washington, giving rivers a chance to recede and residents time to assess damage. Clouds return Sunday with scattered showers, followed by heavy rain on Monday and Tuesday.<\/p>\n
After next week\u2019s Pineapple Express passes through, the system is expected to shift southward.<\/p>\n
\u201cIt will turn into Oregon\u2019s problem, even into Northern California, as we get later into the workweek heading towards Christmas,\u201d Tsaparis said.<\/p>\n
But western Washington is unlikely to see a prolonged dry stretch anytime soon.<\/p>\n
\u201cThis atmospheric river setup isn\u2019t going anywhere,\u201d Tsaparis said. \u201cIt\u2019s just going to be a question of who gets the focus of that very heavy rainfall.\u201d<\/p>\n
Charlie Harger is the host of\u00a0\u00a0on KIRO Newsradio. You can read more of his stories and commentaries\u00a0. Follow Charlie\u00a0\u00a0and email him\u00a0.\u00a0<\/p>\n
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