The interminable ridge parked just off our coast remains in place, keeping the weather dry and the skies mostly cloud-free. On this start to MLK day, we've likely reached peak inversion conditions. What does that mean? Typically, temperatures in a well-mixed atmosphere decrease with height. In the current highly stratified atmosphere, middle- and upper-elevation temperatures are significantly warmer than those at lower elevations and in deeper valley locations. Washington Pass upper station is around 20F warmer than the base, Alpental upper station is 16F warmer than the base, and Mission Ridge is 10F warmer than the base.
Light to moderate easterly gap winds continue, as low cloud/stratus laps at the eastern slopes of the Cascades below 3500 ft on Monday.
The biggest piece of uncertainty is the impact of a weak disturbance sliding down the east slopes of the Rockies Monday night. While all the moisture remains east of our area, it could bring some high clouds over our area overnight into early Tuesday. It will also bring some increased, but mostly light WNW ridgeline winds to some areas. These winds will oppose the persistent low-level E winds through the gaps. At this time, we think higher ridgelines and areas away from gap winds will switch WNW overnight into Tuesday morning. However, the major mountain gaps are more likely to experience reduced easterly wind speeds before they pick back up on Tuesday afternoon.
The disturbance should also bring subtle cooling on Tuesday, but freezing levels remain well above the Cascade Crest.
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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Monday
Sunny and warm at upper elevations. Inversion below 5000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 5500 ft.
Monday
Sunny and warm at upper elevations. Inversion below 5000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 5000 ft.
Monday
Sunny and warm at upper elevations. Inversion below 5000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 5500 ft.
Monday
Sunny and warm at upper elevations. Inversion below 5000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 5500 ft.
Monday
Sunny and warm at upper elevations. Cold and inverted temperatures below 5000 ft. Light to occasionally moderate ridgeline and light E wind at the Pass.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 6000 ft. Light ridgeline and E wind at the Pass.d
Monday
Sunny and warm at upper elevations. Cold and inverted temperatures below 5000 ft. Moderate ridgeline and E wind at the Pass.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 6000 ft. Light to moderate ridgeline and E wind at the Pass.
Monday
Sunny and warm at upper elevations. Cold and inverted temperatures below 7000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 6500 ft.
Monday
Sunny and warm at upper elevations. Cold and inverted temperatures below 7000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 7000 ft.
Monday
Sunny and warm at upper elevations. Cold and inverted temperatures below 7000 ft.
Monday
Night
Mostly clear with a few high clouds overnight and mild. Colder, with temperatures inverted below 7000 ft.
Monday
Sunny and warm at upper elevations. Colder and inverted temperatures below 6500 ft.
Monday
Night
Clear and mild. Colder, with temperatures inverted below 5000 ft.
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).