Heavy Rain, Flood Threat Targets Pacific Northwest, Washington, Oregon

Linda Lam
Published: November 12,2015
The powerful low-pressure system that is sweeping across southern Alaska will bring heavy rain and mountain snow to the Pacific Northwest late this week. This rapidly intensifying storm brought wind gusts in excess of 90 mph to several spots in Alaska earlier this week.
(MORE: Aleutians Cyclone Undergoes Bombogenesis)
This impressive storm will kick off a prolonged period of heavy rain and mountain snow to the region that will last into next week, with rainfall totals in excess of a foot possible.

Rainfall Forecast

The low-pressure system is approaching the Pacific Northwest and a cold front will move through Washington and Oregon Friday into Saturday.
An upper-level trough, or southward dip in the jet stream, will remain over the Pacific Northwest into early next week. This will allow disturbances to move through the region bringing rounds of rain, heavy at times, that will drench the area west of the Cascades in Washington and Oregon over the next week.

Flood Watches and Warnings

The rain will become lighter between systems, but it does not look like it will completely dry out.
Widespread rainfall totals of 3 to 5 inches are expected with up to 10 inches or more in the foothills of the Olympic and Cascade mountains and the coastal range through this weekend. Rain is expected to soak the region through the middle of next week which could possibly send rainfall totals in some areas of western Washington over 18 inches.
(MAPS: Interactive Radar)
The Pacific Northwest has been in a long-term drought, but this rain will be far too much of a good thing.
Flood watches have been issued through Sunday morning for western Washington due to the threat of river flooding from the heavy rainfall.
Some snow fell across portions of the Cascades on Thursday, but snow levels were rising Thursday night, limiting the snow potential.
Snow levels will fall again this weekend behind the cold front. This should allow the Cascade snowpack to build, which is running a little behind average in mid-November.
Winds will be a concern as well with strong southerly winds sustained at 20 to 40 mph with gusts up to 60 mph through Friday night. This may bring down trees, causing power outages. High surf and beach erosion are also possible along the central coast of Washington state. Let's break down the forecast over the next few days.

Friday

Friday's Forecast

Rain will persist across much of Washington and northwest Oregon, with snow in the highest elevations of the Cascades. Gusty winds will also continue in Washington. Rain and snow are also likely in northern Idaho and northwestern Montana.
(FORECAST: Seattle | Coeur d'Alene, Idaho)

Saturday

Saturday's Forecast

Rain and mountain snow will spread farther south through much of western Oregon and into northwestern California while persisting in western Washington. On Saturday night, rain and snow will push south and east into central California, northwestern Nevada, most of Oregon and western Idaho.
(FORECAST: Portland, Oregon | San Francisco)

Sunday

Sunday's Forecast

Much of the West will see the chance of rain and mountain snow by Sunday, with heavy snow possible from the Cascades to the Sierra Nevada.
(FORECAST: South Lake Tahoe, California | Spokane, Washington)
Another low pressure system is expected to approach the Pacific Northwest early next week, which will bring another shot of rain and mountain snow. The flood threat may increase with this next system, due to the rain expected through this weekend.
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