A frontal system will slowly move inland today and tonight, eventually producing stormy conditions across the PNW. The parent upper low off the central B.C. coast will help slow its inland progress and orient the front in a more N-S fashion by day's end. Snowfall rates will increase for the northwest Cascades and Olympics this afternoon with lighter snow developing south and eastward during the daylight hours. Heavy snow will affect most areas this evening as the front slowly sags south. Strong to extreme S-SW winds are expected west of the Cascade crest by this afternoon with strong E-SE winds near the Cascade Passes themselves as cross-Cascade gradients ramp up.
Temperatures have popped up this morning into the 20s at upper elevation sites near and west of the Cascade crest as strong SW winds have pushed relatively warmer air in aloft. As offshore gradients strengthen this afternoon, look for the biting cold air along the east slopes of the Cascades to be pulled back through the Washington Pass area, Snoqualmie, Stevens, and White Pass areas with places further west like Crystal/Paradise cooling in the evening as the heaviest precipitation starts. Mt Hood will largely miss the action on Sunday, but look for heavy precipitation to afflict the central and southern Washington Cascades this evening and then Mt Hood after midnight. Mt Hood will see the brunt of the milder air, with snow levels sticking in the 4000-5000' range. Winds will become extreme late this afternoon through Monday morning in the Mt Hood area as well.
The frontal boundary will hang up around northern Oregon Monday, with heavy precipitation expected through the day. Further north, look for the upper low to rotate moderate showers into the region with significant addition snow accumulations and cool snow levels 0-1000'.
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
Light to moderate snow developing during the day. Winds becoming extreme.
Sunday
Night
Moderate to occasionally heavy snow decreasing late tonight. Strong to extreme winds decreasing in the evening.
Sunday
Light to moderate snow developing and becoming heavy later in the afternoon. Strong winds becoming extreme in the afternoon.
Sunday
Night
Moderate to occasionally heavy snow decreasing late tonight. Strong to extreme winds decreasing after midnight.
Sunday
Light to occasionally moderate snow developing during the day. Winds becoming strong in the afternoon.
Sunday
Night
Moderate to occasionally heavy snow and strong to extreme winds.
Sunday
Cloudy with periods of light snow this morning, then light snow in the afternoon becoming moderate late. SSW Winds increasing and becoming strong to extreme late in the day, Paradise and Crystal areas. Strong E-SE winds White Pass area.
Sunday
Night
Moderate to heavy snow and strong to extreme winds.
Sunday
Cloudy with periods of light snow this morning, then light snow in the afternoon becoming moderate late. Strong east winds at Pass level.
Sunday
Night
Moderate snow. Strong east winds at Pass level.
Sunday
Cloudy with periods of light snow this morning, then light snow in the afternoon becoming moderate late. Strong east winds at Pass level.
Sunday
Night
Moderate to occasionally heavy snow. Strong east winds at Pass level.
Sunday
Cloudy with periods of light snow this morning, then light to moderate snow in the afternoon. Strong ridgeline winds.
Sunday
Night
Moderate snow and strong winds easing late.
Sunday
Cloudy this morning then light snow developing in the afternoon. Moderate to strong ridgeline winds.
Sunday
Night
Moderate snow and strong winds.
Sunday
Cloudy this morning then light snow developing in the afternoon. Moderate to strong ridgeline winds.
Sunday
Night
Moderate snow and strong to extreme winds.
Sunday
Cloudy. Chance of light snow and rain late. Winds becoming strong to extreme late in the day.
Sunday
Night
Moderate rain and snow becoming heavy after midnight. Extreme 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).