The National Weather Service is predicting heavy rain in much of Western Washington over the next two days, which is predicted to cause moderate or major flooding in many Lewis County rivers.
The heavy rain, wind and unseasonably warm weather is courtesy of a pineapple express weather system, now more commonly referred to among meteorologists as an “atmospheric river,” said Andy Haner, meteorologist from the National Weather Service in Seattle.
“Basically you end up with a really strong corridor, or spots of jet stream winds across the Pacific,” he said. “It picks up moisture down in the tropics and very quickly scoots it up here to the Pacific Northwest.”
The term “pineapple express” was first coined to describe jet stream winds, in this case of more than 200 miles per hour, driving moisture and warm temperatures from Hawaii, Haner said. However, he noted this weather system appears to originate closer to the Philippines.
This weather system is predicted to lead to flooding in the Chehalis, Newaukum and Skookumchuck rivers, according to a flood watch bulletin from the National Weather Service.
The lower Chehalis Valley is also at a higher risk of landslides due to recent heavy rains, according to a bulletin from the National Weather Service.
“We’re on this. We’re watching it,” said Steve Mansfield, manager of Lewis County’s Department of Emergency Management. “(Today) we’re supposed to get a little bit of lull and on Wednesday it’s supposed to shoot back up again.”
The Cowlitz River at Randle is also predicted to reach minor flood stage — 18 feet — Tuesday afternoon, and could get as high as 23.9 feet by 10 a.m. Wednesday, nearly 2 feet above the level considered a major flood. The record for the Cowlitz River at Randle is 25.2 feet. It is predicted to recede starting Wednesday afternoon, according to the National Weather Service.
The Chehalis River at Centralia is also predicted to flood, reaching minor flood stage at about 9 p.m. Tuesday and peaking at 69.35 feet — considered a moderate flood — late Wednesday or early Thursday morning.
Downriver, at Grand Mound, the water is predicted to reach major flood stage Wednesday and crest at 17.79 feet through Thursday. The record at that part of the river is 20.2 feet.
Mansfield said residents of the Twin Cities should have plenty of time to prepare for flooding from the Chehalis River.
The Skookumchuck River in Centralia is predicted to crest at 86.7 feet at about 4 p.m. Wednesday, just below major flood stage, which is 86.9 feet. The record flood level for the Skookumchuck is 87.3 feet, according to the National Weather Service.
The Newaukum River at Chehalis is predicted to reach minor flood stage — 10.5 feet — Tuesday night, and reach a high of 13.38 feet at 10 a.m. Wednesday before beginning to recede Wednesday night.
The flood watch is in effect from Tuesday morning through Wednesday afternoon. Flooding is also forecast in areas of Southwest Washington such as the Willapa Hills.
Haner said it normally takes about 36 hours of continuous rainfall to cause a flooding event. However, this storm is operating differently.
“As far as the flooding goes … we’ve got the strong jet stream winds and within the jet streams are these little impulses. … It’s just these 12 hours bursts of rain that come and go and come and go,” he said. “It’s just such a rapid succession of them. The rivers don’t have a chance to drop before the next round of rain comes in.”
Snow levels are expected to rise to 5,500 to 6,500 feet today, and to 8,000 feet Tuesday. The snow level should fall again to 3,500 to 4,500 feet late Wednesday.
•••
Check www.chronline.com for live updates on the flooding situation.
