It's pretty stormy across the mountains this morning. A compact frontal system is running a little behind schedule but seems to have arrived with a vengeance in the pre-dawn hours. Moderate to locally heavy snowfall is impacting sites near and west of the Cascade crest. As the front pushes further east, it should drag precipitation with it.
While it's already windy across the region, look for the winds to turn more westerly and increase behind the front mid-morning. These often strong and gusty post-frontal winds will combine with a relatively unstable and moisture-laden air mass to drive snow showers in the mountains throughout the day. Some of these showers could be locally heavy and produce periods of graupel. A Puget Sound Convergence Zone should also form by mid-day and take aim at the Central Cascades near the Mountain Loop Highway. Expect heavier snowfall rates under this narrow band of precipitation. The surprise for the day could be some significant sun breaks in the afternoon. With an unstable trough overhead, skies should gather into puffy cumulus clouds and allow for sunshine to poke through between those ongoing snow showers.
Overnight, showers and winds should decrease as we enjoy a relative break in the weather ahead of our next storm system.
A developing low pressure will approach the Oregon coast Monday morning; this will have two big effects on the region. This setup could drive relatively strong E-SE winds across the Cascade Crest and Passes. It will also rotate bands of precipitation up into the mountains from the S and SE. This flow pattern often favors locations along the east slopes of the Cascades. While not a major snow producer, areas near and south of I90 could see several more inches of snow pile up on Monday.
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
Snow showers. Light to moderate NW winds becoming W. Sun breaks possible in the afternoon.
Sunday
Night
Mostly cloudy with isolated snow showers.
Sunday
Snow showers throughout the day. Could be heavy at times. Moderate to strong and gusty westerly winds. Sun breaks possible in the afternoon.
Sunday
Night
Mostly cloudy with isolated snow showers. Light to moderate W winds decreasing.
Sunday
Snow throughout the day. Puget Sound Convergence Zone bringing heavier precipitation to the Mountain Loop Highway area. Moderate to strong SW winds decreasing slightly in the afternoon.
Sunday
Night
Mostly cloudy. A Puget Sound Convergence Zone bringing locally heavier precipitation to the Mountain Loop Highway area. Light to moderate W winds decreasing.
Sunday
Snow in the morning becoming showery by mid-day. Showers could be locally heavy at times. Moderate to strong W winds increasing in the afternoon. Sun breaks possible during the day.
Sunday
Night
Mostly cloudy with scattered showers. Light to moderate SW winds.
Sunday
Snow in the morning, becoming more showery by mid-day. Snow showers could be heavy at times. W winds becoming moderate. Sun breaks possible in the afternoon.
Sunday
Night
Mostly cloudy with a few snow showers possible. Light to moderate W winds decreasing. Light E flow developing at Pass level overnight.
Sunday
Snow in the morning, becoming more showery by mid-day. Snow showers could be heavy at times. W winds becoming strong and gusty. Sun breaks possible in the afternoon.
Sunday
Night
Mostly cloudy with snow showers. Light to moderate W winds decreasing. Light E flow developing at Pass level overnight.
Sunday
Snow in the morning, becoming showery. SW winds turning W and increasing. Becoming Moderate to strong and gusty. Sun breaks possible in the afternoon.
Sunday
Night
Partly to mostly cloudy with isolated snow showers. Moderate W winds decreasing.
Sunday
Snow in the morning, heaviest near the crest. Becoming showery. Precipitation could be heavy at times. Strong and gusty W winds. Sun breaks possible, especially in the afternoon.
Sunday
Night
Partly to mostly cloudy with isolated snow showers. Moderate to strong SW wind decreasing.
Sunday
Snow in the morning, heaviest near the crest. Becoming showery. Precipitation could be locally heavy at times. Strong and gusty W winds. Sun breaks possible.
Sunday
Night
Mostly cloudy with isolated snow showers. Moderate to strong W winds decreasing and turning SW.
Sunday
Snow in the morning, becoming more showery. Precipitation could be locally heavy at times. Strong and gusty W winds decreasing slightly in the afternoon. A few sun breaks possible.
Sunday
Night
Mostly cloudy with snow showers. Moderate to strong SW 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).