A vertically stacked low moves onshore over southern Oregon today. The influence of this low has brought colder air into the region along with N flow aloft. A weak shortwave ridge moving in on Tuesday creates some subtleties to the weather pattern today, capping moisture mostly below 9000 ft and limiting it primarily to the west slopes of the Cascades. A band of more continuous showers over northern and central Washington will gradually drift southward as convection helps diversify precipitation around the region in the afternoon. NW winds will also pick up for Mt Hood and the southern Cascade Volcanoes in the afternoon.
A shortwave trough moves into the region Tuesday night into Wednesday. This will keep light snow showers focused on the western sides of our ranges. A converge band likely forms near Snoqualmie Pass Tuesday night and likely shifts northward toward the mountain loop on Wednesday. Models diverge regarding how well this band stays together.
Snow levels will be in the 3000-3500 ft range during the day and drop overnight to 2000-3000 ft. Expect freezing levels to be in the 4000 ft range during the day when showers are not overhead.
Light rain and snow showers, steadiest early in the day.
Tuesday
Night
Light snow showers.
Tuesday
Light rain and snow showers, steadiest in the morning.
Tuesday
Night
Light snow showers and weak convergence.
Tuesday
Light rain and snow showers, increasing in the mid-day and afternoon hours.
Tuesday
Night
Light snow showers.
Tuesday
Light rain and snow becoming showery in the afternoon. Light to moderate ridgeline and light W wind at the Pass.
Tuesday
Night
Light snow showers (steadier and more intense in potential convergence banding). Light ridgeline and W wind at the Pass.
Tuesday
Light rain and snow becoming showery in the afternoon. Light to moderate ridgeline and light W wind at the Pass.
Tuesday
Night
Light snow showers (steadier and more intense in potential convergence banding). Light ridgeline and W wind at the Pass.
Tuesday
A few light rain or snow showers near the Cascade Crest. Otherwise, partly cloudy. Light to moderate ridgeline winds.
Tuesday
Night
Partly cloudy. Light to moderate ridgeline winds.
Tuesday
A few light rain or snow showers near the Cascade Crest. Otherwise, partly cloudy. Light to moderate ridgeline winds.
Tuesday
Night
Mostly cloudy with some convergence spillover (western part). Light to moderate ridgeline winds.
Tuesday
A few light rain or snow showers near the Cascade Crest. Otherwise, partly cloudy. Light to moderate ridgeline winds.
Tuesday
Night
Partly cloudy. Light to moderate ridgeline winds.
Tuesday
Mostly cloudy in the morning. Light snow showers in the afternoon. Light ridgeline winds in the morning. Increasing light to moderate ridgeline winds in the afternoon.
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).