High clouds will stream over the region today in advance of an approaching frontal system with overcast skies for all areas by mid-day. A low pressure system will deepen as it curls towards the central British Columbia coast tonight. Warm frontal moisture will spread inland from the coast overnight, reaching as far south as Mt Hood. As the main frontal boundary sets up into southern B.C., the axis of the heaviest precipitation will shift towards the Canadian border Saturday morning. Forecast models are still struggling with just how much precipitation falls from Stevens Pass and southward during the day on Saturday. On top of a wide range of precipitation total outcomes, mild air blowing in on strong SW winds will battle with cold air entrenched over the Cascades and especially east of the Cascade Crest on Saturday.
Currently, it seems likely there will be a wintry mix including freezing rain for places like Snoqualmie Pass and White Pass from mid-morning Saturday through early afternoon before a switch to rain. Stevens Pass may see a wintry mix late in the day. The rain line should push up to 5000' for the southern Cascades and even higher for Mt Hood on Saturday albeit with lighter precipitation. Along the east slopes of the Cascades, areas north of I-90 should hold onto snow for most of the day, with a potential wintry mix between highway 2 and I-90 later Saturday afternoon. The mountains from Lake Chelan and northward will likely stick as snow all day. Alpine winds will be extreme out of the SW later Saturday as well from the central Cascades and southward.
All in all this is a messy system with a fair amount of uncertainty with precipitation totals to kick off the weekend.
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
Becoming overcast with increasing high clouds this morning.
Friday
Night
Light rain and snow developing and becoming moderate after midnight. Strong winds developing overnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Light rain and snow developing and becoming moderate after midnight. Strong winds developing overnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Light rain and snow developing and becoming moderate after midnight. Strong winds developing overnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight. Strong winds developing late.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight. Light east winds at Pass level becoming moderate after midnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight. Light east winds at Pass level becoming moderate after midnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight. Strong winds developing late.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight.
Friday
Becoming overcast with increasing high clouds this morning.
Friday
Night
Cloudy, then light rain and snow developing after midnight.
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).