Pacific Storm Parade to Lash Northwest With Heavy Rain, Mountain Snow For Days

December 6,2015

A parade of five Pacific storms are expected to rake the Pacific Northwest over the next week.
The combined effect of heavy rain and saturated ground may trigger localized flooding in parts of western Washington and western Oregon, and feet of snow may pile up in the Cascades, and other mountain chains from this Pacific onslaught.

Western Radar

Into Early Monday Morning

A classic November-December setup featuring a powerful jet stream stretching from eastern Asia across the Pacific for 5,000 miles to the Pacific Northwest will act as the conductor for this storm parade ahead.
In fact, winds at jet-stream level over parts of the North Pacific well west of the U.S. were estimated at over 200 miles per hour Friday morning. Talk about a quick flight from Tokyo to Seattle, albeit just a wee bit choppy.
The latest round of rain, wind, and mountain snow continues to impact Washington, Oregon and Northern California as of Sunday night.
NOAA's National Weather Service has issued high wind warnings that are in effect into Monday for parts of the western Washington and Oregon coasts. Wind gusts up to 75 mph are possible at times.
(FORECAST: Seattle | Portland | San Francisco)

The Parade Continues

Infrared satellite imagery shows Pacific storms lined up along the aforementioned powerhouse jet stream.

Pacific Satellite, Pressure and Winds

After the current storm, there are four additional storms in the pipeline for the Northwest and at least northern California in the new week ahead of varying intensity:

• Monday (relatively warm, wet, higher snow levels)
• Late Tuesday into Wednesday (very warm, very wet, high snow levels; then colder with lower snow levels)
• Thursday (colder, low snow levels)
• Next weekend (possibly strong; cold air may hang in low elevations, wet)

While it remains too early to get into all the forecast details, particularly for the latter two systems, the total rain from all five systems from this weekend into next weekend is eventually likely to trigger flooding, in the foothills and lower elevations of western Washington, western Oregon and northwest California. Minor flooding is possible for many rivers, especially in western Washington this week.

This Week's Forecast

Some windward slopes of the Olympics, Cascades and coastal ranges are likely to pick up over 10 inches of total rainfall by late in the week ahead.
The National Weather Service has posted flash flood watches, that are in effect through Wednesday morning across portions of northwestern Oregon and far southwestern Washington.
One other factor contributing to the flood threat is saturated ground, thanks to heavy rain the week before Thanksgiving, triggering major flooding in parts of western Washington.

Rain and Snow Outlook Through Next Sunday

In addition, feet of snow should fall in the Washington Cascades through the week ahead, with some locally heavy snow also piling up over the Bitterroots, Tetons, Siskiyous, Oregon Cascades, and at least parts of the Sierra.
This is good news for a Cascades snowpack that is well below average for early December, from a snow-water equivalent perspective.

With some colder air potentially holding over lower elevations ahead of the storms later in the week ahead, a period of freezing rain, sleet or snow can't be ruled out not simply over the colder interior of eastern Washington and eastern Oregon, but also in the Columbia Gorge and possibly along parts of the Interstate 5 corridor, including parts of the Seattle and Portland metro areas.
This is a pattern that was noticeably, largely absent last fall, winter and spring along the West Coast. Blocking high pressure aloft diverted the jet stream away from the U.S. West Coast last season, leading to the record-paltry Cascades and Sierra spring snowpack.
For the latest information on this complex setup, regularly check back to weather.com for updates.

Storm Reports: Heavy Icing Tuesday Night, Wednesday

The first in the series of impactful weather systems arrived in the region this past Tuesday night into early Wednesday.
Freezing rain accumulations of a half inch thick were reported near Skamania, Washington. In Oregon, Troutdale saw ice accumulations of up to one quarter inch thick.
Ice and snow in eastern Oregon from the storm forced school cancelations in Hermiston, Pendleton, Umatilla, Boardman, Milton-Freewater and elsewhere, The Associated Press reported. Icy roads in the Columbia River Gorge also closed or delayed schools on both sides of the Oregon-Washington line.

Wind Reports: Thursday, Saturday

On Thursday, Mount Lincoln in the Sierra of California reported a gust to 106 mph at 2:20 p.m. PST, with sustained winds as high as 74 mph earlier in the afternoon. Squaw Peak in southern Oregon recorded a wind gust of 107 mph just after 8:30 a.m. PST, with sustained winds of 80 mph an hour earlier.

A look at reported wind gusts on Thursday across the area.

Typically windy spots along the Oregon coast also reported strong wind gusts, with Mount Hebo clocking a 72-mph gust just after 9 a.m. PST Thursday.
The greater Reno area had reported just over 5,000 power outages around midday Thursday, most of the power had been restored by Thursday evening. A semi truck flipped over about 5 miles east of town, where local authorities believed high winds were the cause.
Winds were strong enough to partially blow off a metal roof from a structure near Montague, California. In Brookings, Oregon, the National Weather Service relayed reports of down fences, blown in window panes and other minor damage.
The next round of wind on Saturday was much less intense than what was observed two days prior. Although winds gusted to 78 mph atop Crystal Mountain in western Washington Saturday morning, most other wind gusts remained below 60 mph across the region.
MORE: Northwest Powerful Wind Storm, Nov. 18, 2015