Pesky light scattered snow showers and low level clouds will define this morning with NW flow aloft and cold temperatures settled over much of the region. The coldest air is located across the northern half of the region, where mountain temperatures are commonly in the single digits. We may see some partly sunny skies break out between the Mt Baker area and Washington Pass this afternoon as showers decrease. High clouds will continue to stream in for the rest of the region from the WSW in advance of the next system.
The broad upper low that has carved a longwave trough over the PNW will become more zonal, or westerly tonight and Tuesday. Practically speaking, this will open the door for a developing frontal system to quickly move through the region, traversing quickly from west to east tonight and Tuesday.
Warm frontal moisture, generally light snow, will move over the region tonight with snowfall rates ramping up Tuesday morning for the north Cascades and heavier precipitation spreading south mid-day and Tuesday afternoon as the cold front begins to sweep through. There is still quite a bit of uncertainty with the track of the low, but right now the central Washington Cascades are most likely to see the heaviest precipitation, with lower confidence near the Canadian border and south of Snoqualmie Pass. With cold temperatures entrenched over the region, look for high snow to water ratios, i.e. low density snow. Some locations will likely see up to 2 ft by Tuesday afternoon. One caveat is a subtle warming trend for areas south of the low on Tuesday afternoon. Right now, that's most likely to impact the Mt Hood area and perhaps the SW Cascades away from the Cascade crest. W-SW winds will also ramp up with this system as well.
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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Monday
Cloudy with scattered light snow showers.
Monday
Night
Light snow developing and becoming moderate by late tonight. Winds becoming strong.
Monday
Mostly cloudy with scattered light snow showers this morning, becoming partly sunny this afternoon.
Monday
Night
Light snow developing and becoming moderate by late tonight. Winds becoming strong.
Monday
Cloudy with scattered light snow showers.
Monday
Night
Light snow developing and becoming moderate by late tonight. Winds becoming strong.
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).