A low-pressure system off the Oregon coast will keep mostly cloudy skies over our region with an increasing chance of showers as it lifts northeast. A lingering disturbance maintains a chance of very light snowers near the Washington / British Columbia border early Friday. These showers should dissipate, leaving fair weather for much of central and northern Washington through the mid-day hours. A cold-frontal feature increases more widespread shower activity from south to north during the afternoon. Temperatures started the day mild with only upper elevations (above around 6000 ft) below freezing. Temperatures should stay fairly steady throughout the day with only weak inversions and lower elevations showering much in the way of diurnal warming.
The main event arrives Friday night as the NNW-SSE oriented lifts northward. Light to moderate SE winds aloft, combined with low-level E flow should favor the E slopes of the Cascades for a period of moderate precipitation, but the west slopes of the Cascades should still do fairly well. Expect some cooling as snow levels lower to and remain around 4000 ft on Saturday. The frontal band lingers over northern Washington. Weather models diverge regarding how far north this frontal band lifts and how much shower activity continues for the central Washington Cascades. It could be the difference between a fairly dry day vs a fairly wet/snowy one.
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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Friday
Mostly cloudy with an increasing chance of light rain or snow showers. Mild.
Friday
Night
Periods of light rain and snow (moderate in southern and eastern Olympics).
Friday
Mostly cloudy with a chance of light rain or snow showers. Mild.
Friday
Night
Periods of light rain and snow.
Friday
Mostly cloudy with a chance of light rain or snow showers. Mild.
Friday
Night
Periods of light rain and snow becoming moderate at times after midnight.
Friday
Mostly cloudy in the morning. Light rain or snow showers increase from mid-morning onward. Mild.
Friday
Night
Light rain and snow. Light to moderate rain and snow with the peak precipitation shifting from south to north.
Friday
Mostly cloudy with a chance of light rain or snow showers, mainly during the afternoon hours. Light ridgeline and light E wind at the Pass. Mild.
Friday
Night
Light rain and snow become moderate overnight. Light ridgeline and E wind at the Pass shift W overnight.
Friday
Mostly cloudy with a chance of light rain or snow showers, mainly during the afternoon hours. Increasing light to moderate ridgeline and light to occasionally moderate E wind at the Pass. Mild.
Friday
Night
Light rain and snow become moderate overnight. Light ridgeline and E wind at the Pass shift W overnight.
Friday
Mostly cloudy with some filtered sunshine at times; a slight chance of light rain or snow showers. Mild.
Friday
Night
Increasing light rain and snow.
Friday
Mostly cloudy with some filtered sunshine at times; a chance of light rain or snow showers in the afternoon. Mild.
Friday
Night
Increasing light rain and snow become moderate overnight.
Friday
Mostly cloudy with some filtered sunshine at times; a chance of light rain or snow showers in the afternoon. Mild.
Friday
Night
Light to moderate rain and snow.
Friday
Mostly cloudy with increasing chances of light rain or snow showers. Mild. Light to moderate ridgeline winds.
Friday
Night
Moderate rain and snow decrease into the light range overnight. Light to 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).