A slow-moving upper-level trough will cross the north Cascades this morning and leftover isolated showers along the west slopes of the Cascades and near the Canadian border will come to an end later this morning. Look for low clouds to break up but not completely clear out along the west slopes of the Cascades from the border down to near and west of Snoqualmie Pass and the eastern portion of Hwy20. Sunnier conditions will prevail elsewhere but we'll see some high clouds advancing from the SW in the afternoon for areas like Mt Hood, the Olympics and the south WA Cascades. Freezing levels dropped overnight, settling around 3000-3500' this morning and will only see a modest rise to 4000-4500' this afternoon. Worth noting is the colder temperatures at higher elevations, our highest weather stations above 7000' are showing temperatures in the teens or even single digits...some of the colder reports we've seen in quite awhile.
We'll ring in the New Year without much fanfare weather-wise. High clouds from the next frontal system will start to encroach on the area from the west Monday afternoon. Offshore gradients will increase, starting a round of east flow through the Cascade Passes. While wind speeds are unremarkable during the daylight hours, we should see some low clouds develop along the east slopes of the Cascades start to approach the Cascades Passes. While the lower slopes forecast for the Cascade Passes is uncertain, clearer conditions from mid-mountain up look like a better bet. Mt Hood will be the mild spot in the forecast area, with freezing levels in the 5000-6000' from Sunday afternoon through Monday afternoon.
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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Sunday
Mostly sunny with increasing high clouds in the afternoon.
Sunday
Night
Cloudy then becoming mostly clear late tonight.
Sunday
Mostly cloudy with isolated light rain and snow showers in the morning. Partly sunny to mostly cloudy in the afternoon.
Sunday
Night
Cloudy then becoming mostly clear late tonight.
Sunday
Mostly cloudy with isolated light rain and snow showers in the morning. Partly sunny to mostly cloudy in the afternoon.
Sunday
Night
Cloudy then becoming partly cloudy late tonight.
Sunday
Partly to mostly cloudy with isolated light rain and snow showers in the morning, then mostly sunny around mid-day. Increasing high clouds in the afternoon.
Sunday
Night
Cloudy then becoming partly cloudy late tonight.
Sunday
Mostly cloudy with isolated light rain and snow showers in the morning, then partly sunny around mid-day. Increasing high clouds later in the afternoon. Light west winds at Pass level and ridgeline.
Sunday
Night
Cloudy then becoming mostly cloudy late tonight. Light east winds at Pass level, light west winds at ridgeline.
Sunday
Mostly cloudy with isolated light rain and snow showers in the morning, then partly sunny around mid-day. Increasing high clouds later in the afternoon. Light to moderate west winds at Pass level and ridgeline.
Sunday
Night
Cloudy then becoming mostly cloudy late tonight. Light east winds at Pass level, light west winds at ridgeline.
Sunday
Mostly cloudy with isolated light rain and snow showers in the morning. Partly sunny to mostly cloudy in the afternoon.
Sunday
Night
Cloudy.
Sunday
Partly cloudy with isolated light rain and snow showers in the morning. Mostly sunny in the afternoon.
Sunday
Night
Cloudy.
Sunday
Mostly sunny with increasing high clouds later in the afternoon.
Sunday
Night
Cloudy.
Sunday
Mostly sunny with increasing high clouds in the afternoon. Moderate ridgeline winds easing this afternoon.
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).