Anomalously cold air continues to move into the Pacific Northwest this holiday season. An anomalously strong high pressure over the North Pacific has created the ideal conditions for modified arctic air to move into our region. Northerly flow sweeps down from the Yukon, picking up some moisture and generating instability (clouds and weak lows), which rotate around a trough and into our region. Saturday night, generally light to occasionally moderate snow shower activity continues across the Cascades. A boundary between deep Fraser River outflow and southerly winds ahead of the trough axis seems to have produced moderate to heavy convergence snowfall across western Watcom County. We're keeping an eye on the potential for this to shift eastward and bring snowfall amounts that may be higher than our current 3-8" forecast for Mt. Baker overnight. We expect 3-8" at Snoqualmie Pass, Paradise, and Mt. Hood Saturday night as well.
The large-scale setup changes slowly over the short-term forecast period. We're watching the track of a weak low just off the central Vancouver Island coastline, spinning SE toward our region. The exact track of this low will determine how quickly and how much modified arctic air spills into the region and how quickly the moisture and mostly light snow shower shuts off Sunday and Sunday night. At the moment, most models take the low toward southern Washington. This will help suck the cold air from interior British Columbia into our region, making Sunday dangerously cold in all mountain locations with 5000 ft highs temperatures only reaching the single digits or teens. We do still expect moderate snow showers to continue for Mt. Hood and possibly the southern Washington Volcanoes on Sunday with decreasing light winds.
The trough axis shifts should be over our area with clearing skies and light/variable winds. Light snow shower activity tapers to flurries and ends Sunday night. Temperatures will plummet, resulting in a slew of record low temperatures on Monday morning which will continue into a slew of record low high temperatures on Monday. Temperatures will be bitterly cold at all elevations.
Weather Forecast
Olympics
West North
West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
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Saturday
Night
Light to moderate snow, heaviest in Olympic foothills with upslope flow. Very cold.
Sunday
Decreasing light to occasionally moderate snow. Very cold.
Saturday
Night
Light to moderate snow showers, possibly heavy in convergence.
Sunday
Light snow showers.
Saturday
Night
Light to occasionally moderate snow showers.
Sunday
Light snow showers.
Saturday
Night
Light to moderate snow showers, heaviest at Paradise.
Sunday
Light to moderate snow showers, heaviest at Paradise.
Saturday
Night
Light snow showers. Light and variable wind at the Pass.
Sunday
Light snow showers. Light and variable wind at the Pass in the morning, then switching westerly.
Saturday
Night
Decreasing light to moderate snow showers. Light and variable wind at the Pass.
Sunday
Light snow showers. Light and variable wind at the Pass in the morning, then switching westerly.
Bitterly cold weather will continue, but temperatures should not be quite as cold as Monday. A weak shortwave passes Monday night, bringing clouds to much of the region and a chance of very light snowfall in the western Olympic Mountains and the southern Cascades into Tuesday morning. Conditions dry out fully once again, through Wedesday.
The NWAC program is administered by the USDA-Forest Service and operates from the National Weather Service Forecast Office in Seattle. NWAC services are made possible by important collaboration and support from a wide variety of federal, state and private cooperators.
The 5000’ temperature forecast does not imply a trend over the 12 hr period and only represents the max and min temperatures within a 12 hr period in the zone. The 6-hr snow level forecast, the forecast discussion, and weather forecast sections may add detail regarding temperature trends.
The snow level forecast represents the general snow level over a 6 hr time period. Freezing levels are forecast when precipitation is not expected.
*Easterly or offshore flow is highlighted with an asterisk when we expect relatively cool east winds in the major Cascade Passes. Easterly flow will often lead to temperature inversions and is a key variable for forecasting precipitation type in the Cascade Passes. Strong easterly flow events can affect terrain on a more regional scale.
Ridgeline winds are the average wind speed and direction over a 6 hr time period.
The wind forecast represents an elevation range instead of a single elevation slice. The elevation range overlaps with the near and above treeline elevation bands in the avalanche forecast and differs per zone.
Wind direction indicates the direction the wind originates or comes from on the 16-point compass rose.
Water Equivalent (WE) is the liquid water equivalent of all precipitation types; rain, snow, ice pellets, etc., forecast to the hundredth of an inch at specific locations. To use WE as a proxy for snowfall amounts, start with a snow to water ratio of 10:1 (10 inches of snow = 1 inch WE). Temperatures at or near freezing will generally have a lower ratio (heavy wet snow) and very cold temperatures can have a much higher ratio (dry fluffy snow).