For most locations, Sunday will be a bit of the proverbial "calm before the storm." Clouds should continue to increase and thicken throughout the day as the bulk of the storm starts to approach the Pacific Northwest. While you may encounter a few stray showers, most of the precipitation should hold off until later in the afternoon. The major exception to this pattern is Mt Baker and the Olympics. A weak front sits dropped across the tip of the Olympic Peninsula and North Cascades this morning. This should provide ample moisture and strong southerly winds for locations near and north of Hwy 20.
The main event should begin for most areas in the evening hours as a warm front arrives with a very strong westerly jet stream. Expect extremely stormy conditions to develop overnight with strong and gusty winds, periods of heavy rain and snow, and fluctuating freezing levels. With such favorable dynamics, precipitation should easily spill over the mountains to locations further east.
As we head into Monday morning, the storm will rage on, with the rain snow-line hovering near Stevens/White Passes and well above Snoqualmie Pass. A trailing cold front will sweep across the region during the morning hours and send snow levels falling below all pass levels. Look for periods of heavy precipitation and very strong winds to accompany the frontal passage. With the jet stream aimed at the Cascades and plenty of moisture in places, moderate post-frontal snow will continue throughout the day. This storm looks like a good snow producer for the mountains with many sites receiving 1-2 feet of snow before we start to dry up on Tuesday.
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 rain and snow increasing in the afternoon. Moderate to strong SW winds.
Sunday
Night
Stormy with rain and snow, heavy at times. Strong and gusty SW winds.
Sunday
Stormy with rain and snow, heavy at times. Precipitation increasing in the afternoon. Moderate to strong S winds, increasing and becoming gusty later in the day.
Sunday
Night
Stormy with ran and snow, very heavy at times. Strong and gust S winds becoming SW.
Sunday
Periods of rain and snow, particularly in the northern half of the zone. Precipitation increasing in the afternoon. Moderate to strong SW winds.
Sunday
Night
Stormy with rain and snow, heavy at times. Strong and gusty SW winds inceasing overnight.
Sunday
Mostly cloudy in the morning with showers increasing in the afternoon. Heaviest near Mt Rainier. Light to moderate SW winds.
Sunday
Night
Stormy with rain and snow, heavy at times. Moderate to strong SW winds increasing and becoming very gusty overnight.
Sunday
Mostly cloudy in the morning with showers increasing during the day. Light WSW winds becoming moderate in the afternoon.
Sunday
Night
Stormy with rain and snow, heavy at times. Moderate SW winds could be very gusty overnight.
Sunday
Mostly cloudy in the morning. Showers increasing in the afternoon. Light to moderate WSW winds increasing and becoming gusty later in the day.
Sunday
Night
Stormy with rain and snow, heavy at times. Moderate SW winds could be very gusty overnight.
Sunday
Mostly cloudy in the morning with showers increasing in the afternoon. Light to moderate SW winds increasing later in the day.
Sunday
Night
Stormy with rain and snow. Moderate SW winds could be very gusty at times.
Sunday
Partly to mostly cloudy in the morning. Clouds increasing and thickening in the afternoon with a few showers near the Crest. Light to moderate WSW winds increasing later in the day.
Sunday
Night
Stormy, with rain and snow heaviest near the Crest. Winds increasing and becoming strong and gusty overnight.
Sunday
Partly to mostly cloudy with a few isolated showers possible near the Crest. Clouds thickening and lowering. Moderate WSW winds.
Sunday
Night
Cloudy with rain and snow showers. SW winds becoming strong and gusty overnight.
Sunday
Mostly cloudy in the morning with clouds increasing and thickening. A few sprinkles could be possible during the day. Winds quickly becoming WSW moderate to strong.
Sunday
Night
Stormy with periods of heavy rain and snow. Very strong and gust WSW winds. Extreme winds expected in the alpine.
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).