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    Pacific river of moisture to focus flood threat on Northern California early this week

    By Alex Sosnowski, AccuWeather senior meteorologist
    February 18, 2017, 11:51:09 PM EST


    One storm after another will roll in from the Pacific Ocean and across the northwestern United States, causing more travel problems and flooding from heavy precipitation, early this week.

    Much of Washington, Oregon and northern California will get a break from substantial precipitation through the first part of this weekend. However, the break will be short-lived.

    Storms will resume across the Northwestern states later this weekend.

    "The storms will have significant impacts on Washington and Oregon from Sunday through Tuesday with rounds of drenching low-elevation rain and mountain snow," according to AccuWeather Senior Meteorologist Brett Anderson.

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    "Northern California is likely to be slammed again as it appears the heaviest rain from the storms will target the region at the start of next week," Anderson said.

    While the storms will bring the risk of mudslides and avalanches, the greatest threat to lives and property will be from flooding.

    There is the potential for 3 to 6 inches of rain to fall on the mountains, below snow level from Sunday to Monday over the northern half of California.

    "Similar totals will be measured around the San Francisco Bay area and a part of the Sacramento Valley," AccuWeather Senior Meteorologist Kristina Pydynowski said.

    This new dose of heavy rain combined with prior heavy rain this season will aggravate the flooding situation. Many reservoirs are at full capacity. Many rivers are near or above flood stage.

    The full reservoirs are forcing officials to release water downstream that would normally be captured.

    People living along streams and rivers are encouraged to monitor the situation closely.

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    A general 1 to 3 inches of rain will fall from the lower western slopes of the Cascades to the Washington and Oregon coasts.

    Heavy snow will fall over the mountains. Snow levels are likely to be low enough during all or part of the period during early next week to cause slippery travel over the major passes in the Cascades and northern Sierra Nevada from Washington to Northern California.

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    Episodes of snow and an icy mix will also lead to travel hazards over the interior Northwest, east of the Cascades for a time next week.

    “Above 7,500 feet, two feet will be common with four feet in places. For highway I-80 at Donner Summit, the precipitation could fluctuate between heavy snow and heavy rain and it could be mixed for a significant fraction of the time," AccuWeather Meteorologist Jim Andrews said.

    Gusty winds and soggy soil will allow some trees to be knocked over, which can lead to sporadic power outages.

    There are some signs the pattern may break for part of the Northwest later next week as colder air begins to push southward.

    "Drier air will push across Washington and Oregon from Canada later next week," Anderson said.

    Static Late Next Week NW

    There is some uncertainty as to how far south this dry air will push. It may not be dry all across the Northwest, despite the pattern change.

    Additional rain and mountain snow may fall on Northern California from Tuesday to Thursday.

    It may take until late next week or next weekend before the wet weather ends for more than a day or two south of Oregon.

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