A persistent offshore upper-level high becomes a ridge on Tuesday before shifting toward the coast. This will bring us more sunny and clear weather.
Broad-scale subsidence keeps us in a highly stratified atmosphere with an inversion in place. This gives us primary freezing levels in the 10,000-11,000 ft range, with secondary freezing levels in the 4000-5000 ft range. If you're below this secondary freezing level, expect frigid temperatures near and east of the Cascade Crest. Mazama takes the cake once again for the coldest temperature at 0F. Temperatures within this cold pool are generally similar to this time Monday morning, but temperatures above 5000 ft are generally 3-10F warmer. Tuesday will be the warmest day of the week in most of these middle and upper-elevation locations, with highs in the upper 40s to mid-50s. Inversions should weaken in the afternoon hours, but don't expect colder valleys to warm much (or at all) above freezing. Low-level easterly flow also peaks Tuesday morning (light to moderate) and gradually decreases through Wednesday morning.
It is worth noting that NNE winds on Mt Hood are moderate to strong early Tuesday. This is likely caused by an interaction with the inversion and these winds should decrease as the inversion mixes out.
On Wednesday light WNW ridgeline winds gradually round the top of the offshore ridge as it flattens, bringing in gradual cooling at upper levels, but low levels along the east slopes of the Cascades and through the mountain gaps should warm relative to Tuesday.
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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Tuesday
Sunny and unseasonably warm with cooler air below the 4500 ft inversion.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cooler air below the 4500 ft inversion.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cooler air below the 4500 ft inversion.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cooler air below the 4500 ft inversion.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cooler air below the 4500 ft inversion. Decreasing light ridgeline and E wind at the Pass.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again. Decreasing light ridgeline and E wind at the Pass.
Tuesday
Sunny and unseasonably warm with cooler air below the 4500 ft inversion. Decreasing light to moderate ridgeline and E wind at the Pass.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again. Decreasing light ridgeline and E wind at the Pass.
Tuesday
Sunny and unseasonably warm with cold air below the 5000 ft inversion partially mixing out in the afternoon.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cold air below the 5000 ft inversion partially mixing out in the afternoon.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cold air below the 5000 ft inversion partially mixing out in the afternoon.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
Tuesday
Sunny and unseasonably warm with cooler air below the 5000 ft inversion. Decreasing moderate ridgeline winds.
Tuesday
Night
Clear and mild, with a low-level cold pool forming once again.
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).