An upper trough slowly rotates toward the Pacific Northwest on Sunday, bringing increasingly cloudy weather and chances for light rain or snow in southern portions of the forecast region. Sunday started mild in most areas except locations east of the Cascade Crest, particularly valley locations where temperatures dropped below freezing.
Upper-level winds are southerly ahead in advance of trough with E low-level flow peaking during the morning hours. This should generate some periods of moderate E-SE winds for the Cascade Crest from around I-90 southward. Foothill locations west of the Crest could see moderate winds and strong gusts at times. With mild conditions already in place, these same locations experiencing downslope winds will also experience the mildest temperatures. Freezing levels should remain around 5000-6000 ft for most of the day, but as light rain/snow spreads into Mt Hood and then the southern Washington Cascades from mid-morning into the afternoon hours, snow levels should drop to around 4500-5000 ft.
Overnight, periods of increasing light rain/snow spread throughout the region from the SW as the trough axis moves into the near-shore waters. Snow levels gradually lower to around 3500-4000.
The trough moves onshore Monday with continued periods of light snow becoming slightly more showery as the trough moves overhead. Snow levels should be in the 3000-4000 ft range. Moderate WSW ridgeline winds peak in morning hours for southern portions of the forecast region with mostly light winds further north.
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
Mild. Mid-level clouds lower and thicken with a slight chance of light rain/snow late in the day.
Sunday
Night
Light rain/snow at times.
Sunday
Mild. Mid-level clouds lower and thicken.
Sunday
Night
Increasing light rain/snow at times.
Sunday
Mild. Mid-level clouds lower and thicken.
Sunday
Night
Increasing light rain/snow at times.
Sunday
Mild. Mid-level clouds lower and thicken with increasing chances of light rain/snow from late morning onwards.
Sunday
Night
Increasing light rain/snow. Moderate ridgeline winds near the Cascade Crest.
Sunday
Mild. Mid-level clouds lower and thicken. Light to occasionally moderate ridgeline and E wind at the Pass.
Sunday
Night
Increasing light rain/snow at times. Light ridgeline and E wind becoming variable at the Pass.
Sunday
Mild. Mid-level clouds lower and thicken. Light to moderate ridgeline and E wind at the Pass.
Sunday
Night
Increasing light rain/snow at times. Light ridgeline and E wind becoming variable at the Pass.
Sunday
Mild. Mid-level clouds lower and thicken.
Sunday
Night
Cloudy in the evening with periods of light rain/snow overnight.
Sunday
Mild. Mid-level clouds lower and thicken.
Sunday
Night
Periods of light rain/snow.
Sunday
Mild. Mid-level clouds lower and thicken with increasing chances of light rain/snow in the afternoon.
Sunday
Night
Periods of light rain/snow.
Sunday
Lowering and thickening mid-level clouds with increasing light rain/snow from mid-morning onwards.
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).