Monday will bring a spring-like day to the mountains with very subtle ridging over the area. To start the day, light winds have allowed cold air (generally in the 20s) to settle into valleys and lower elevations, while ridgelines and middle elevations are milder (largely in the 30s). Washington Pass has a 15°F inversion between our base and summit weather stations. The weather starts to change on Monday, first with thin high clouds thickening in the afternoon, then with gradually increasing but light ridgeline winds. Most locations will start the day sunny, and it may once again feel very spring-like. However, high clouds drift in from the WSW and thicken throughout the day. Temperatures will show a diurnal signal as inversions mix out by 10 AM, and 5000 ft temperatures generally rise into the 40s by the afternoon (and perhaps a few 50s down by Mt Hood).
Clouds gradually lower thicken Monday night, with SW winds increasing. In most areas, these winds remain light, but push into the moderate range for Mt Hood, the Olympics, and Mt Baker areas. A warm front spreads precipitation into the mountains in the early morning hours on Tuesday, starting with NW Washington. Precipitation likely starts with snow levels around 3000 ft, but quickly rises with the warm frontal passage on Tuesday morning, changing snow to rain as it spreads throughout the region. Expect moderate to occasionally heavy rain and high-elevation snow along the western slopes of the Cascades, peaking in the mid-day and afternoon hours, with plenty of moisture reaching east of the Cascade Crest. The cold front likely crosses the Olympics late in the afternoon and the Cascades early in the evening.
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
Mostly sunny with thin high clouds thickening in the afternoon. Mild.
Monday
Night
High clouds lower and thicken with light rain and snow developing in the early morning hours.
Monday
Mostly sunny with thin high clouds thickening in the afternoon.
Monday
Night
High clouds lower and thicken with light rain and snow developing in the early morning hours. Increasing light to moderate ridgeline winds.
Monday
Mostly sunny with thin high clouds thickening in the afternoon. Mild.
Monday
Night
High clouds lower and thicken.
Monday
Mostly sunny with thin high clouds thickening in the afternoon. Mild.
Monday
Night
High clouds lower and thicken.
Monday
Mostly sunny with thin high clouds thickening in the afternoon. Mild. Light ridgeline and W wind at the Pass.
Monday
Night
High clouds lowering and thickening. Increasing light to occasionally moderate ridgeline and light W wind at the Pass.
Monday
Mostly sunny with thin high clouds thickening in the afternoon. Mild. Light ridgeline and W wind at the Pass.
Monday
Night
High clouds lowering and thickening. Increasing light to occasionally moderate ridgeline and light W wind at the Pass.
Monday
Mostly sunny with thin high clouds thickening late in the day. A strong inversion to start the day mixes out by around 10 AM.
Monday
Night
High clouds lowering and thickening.
Monday
Mostly sunny with thin high clouds thickening late in the day.
Monday
Night
High clouds lowering and thickening.
Monday
Mostly sunny with thin high clouds thickening late in the day.
Monday
Night
High clouds lowering and thickening.
Monday
Mostly sunny with thin high clouds thickening late in the day.
Monday
Night
High clouds lowering and thickening. Increasing moderate ridgeline winds.
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).