Issued: 2:09 PM PST Sunday, December 27, 2020
by Robert Hahn

Jump to: Weather Forecast I Precipitation I Snow Level I 5000' Temps I Ridgeline Winds I Extended Weather

Weather Synopsis

The subtropical jetstream is taking the storm track south into California, leaving our region under high pressure through Tuesday.

The warm front that brought clouds and light precipitation to the region on Sunday should exit north by Sunday evening, leaving milder temperatures to the west of the Cascade Crest. E gradients peaking Sunday evening and driving decreasing light to moderate E flow through the passes. Expect inversion conditions to develop in many areas on Sunday night with strong radiational cooling under clear skies with light winds aloft throughout the region. East flow will keep areas near the Cascade Crest cool as it draws a strengthened east side cold pool through the mountain gaps.

Monday should have a chilly start, but temperatures should moderate throughout the region with above freezing 5000 ft temperatures by afternoon in many areas west of the Crest and even in some cases near the Cascade Crest as E flow becomes light and variable.

Monday night should also be clear with very light winds, but not as cold.

Mid-level clouds work into the region ahead of an approaching system on Tuesday.

Weather Forecast

Olympics
West North
West Central
West South
Stevens Pass
Snoqualmie Pass
East North
East Central
East South
Mt. Hood
Use dropdown to select your zone
Sunday Night Partly cloudy early, then becoming mostly clear. Significantly milder with temperatures rising above freezing at 5000 ft. Low cloud possible in the valleys.
Monday Sunny and mild.
Sunday Night Partly cloudy before midnight then becoming mostly clear.
Monday Mostly clear early with mid-level clouds passing around mid-day.
Sunday Night Partly cloudy in the evening, then becoming mostly clear.
Monday Mostly sunny with some high clouds.
Sunday Night Mostly clear.
Monday Decreasing filtered sunshine, then becoming clear.
Sunday Night Decreasing clouds and becoming mostly clear aloft. Low cloud and inversion conditions likely. Decreasing light E flow at pass level.
Monday Mostly clear and cold early with low clouds and inversion mixing out by late morning, then becoming milder. Light E winds at pass level becoming variable late in the day.
Sunday Night Decreasing clouds and becoming mostly clear aloft. Low cloud and inversion conditions likely. Decreasing light to moderate E flow at pass level.
Monday Mostly clear with low clouds and inversion mixing out by late morning, then milder. Light E winds at pass level possibly becoming variable late in the day.
Sunday Night Mostly clear aloft. Low clouds in the valleys with an inversion.
Monday Mostly clear early with increased mid-level clouds in the afternoon.
Sunday Night Mostly clear aloft with low clouds in the valleys with an inversion.
Monday Mostly clear aloft with low clouds in the valley decreasing as inversion conditions relax.
Sunday Night Mostly clear aloft with low clouds in the valleys with an inversion.
Monday Mostly clear aloft with low clouds in the valley decreasing as inversion conditions relax.
Sunday Night Mostly clear with high clouds increasing after midnight. Low clouds in the valleys with an inversion.
Monday Mostly clear aloft with some high clouds. Low clouds and inversion conditions diminishing through the morning hours.

Issued: 2:09 PM PST Sunday, December 27, 2020

Precipitation (in)

Sunday Night Monday Monday Night Tuesday
4 pm - 4 am 4 am - 4 pm 4 pm - 4 am 4 am - 4 pm
Hurricane Ridge 0 0 0 0
Mt Baker Ski Area 0 0 0 0
Mt. Loop - Barlow Pass 0 0 0 0
Stevens Pass 0 0 0 0
Snoqualmie Pass 0 0 0 0
Crystal Mt 0 0 0 0
Paradise 0 0 0 0
White Pass 0 0 0 0
Washington Pass 0 0 0 0
Mission Ridge 0 0 0 0
Salmon la Sac - Gallagher Head 0 0 0 0
Tieton River - Darland Mt. 0 0 0 0
Mt Hood Meadows 0 0 0 0
Timberline 0 0 0 0
Hurricane Ridge Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Mt Baker Ski Area Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Mt. Loop - Barlow Pass Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Stevens Pass Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Snoqualmie Pass Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Crystal Mt Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Paradise Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
White Pass Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Washington Pass Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Mission Ridge Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Salmon la Sac - Gallagher Head Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Tieton River - Darland Mt. Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Mt Hood Meadows Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0
Timberline Precipitation (in)
Sunday Night 0
Monday 0
Monday Night 0
Tuesday 0

Issued: 2:09 PM PST Sunday, December 27, 2020

Snow Level (ft)

Sunday Evening* Sunday Night* Monday Morning* Monday Afternoon* Monday Evening Monday Night Tuesday Morning Tuesday Afternoon
Olympics 4500' 4500' 5000' 5500' 4000' 4000' 4000' 4500'
West North 4000' 3500' 3500' 4500' 3500' 2500' 2500' 3000'
West Central 3500' 3000' 3500' 5000' 3500' 2500' 2500' 3500'
West South 3500' 3000' 3000' 5500' 3500' 3000' 3000' 4000'
Stevens Pass 2500' 2000' 2000' 4000' 3000' 2500' 2500' 3500'
Snoqualmie Pass 3000' 2000' 3000' 4500' 3000' 2500' 2500' 3500'
East North 2000' 2000' 2000' 3500' 3000' 2500' 2000' 3000'
East Central 2500' 2000' 2000' 3500' 3000' 2500' 2500' 3500'
East South 2500' 2000' 2000' 4500' 3500' 3000' 3000' 4500'
Mt. Hood 3500' 3000' 3000' 4500' 4000' 4000' 4000' 5500'
Olympics Elevation
Sunday Evening* 4500'
Sunday Night* 4500'
Monday Morning* 5000'
Monday Afternoon* 5500'
Monday Evening 4000'
Monday Night 4000'
Tuesday Morning 4000'
Tuesday Afternoon 4500'
West North Elevation
Sunday Evening* 4000'
Sunday Night* 3500'
Monday Morning* 3500'
Monday Afternoon* 4500'
Monday Evening 3500'
Monday Night 2500'
Tuesday Morning 2500'
Tuesday Afternoon 3000'
West Central Elevation
Sunday Evening* 3500'
Sunday Night* 3000'
Monday Morning* 3500'
Monday Afternoon* 5000'
Monday Evening 3500'
Monday Night 2500'
Tuesday Morning 2500'
Tuesday Afternoon 3500'
West South Elevation
Sunday Evening* 3500'
Sunday Night* 3000'
Monday Morning* 3000'
Monday Afternoon* 5500'
Monday Evening 3500'
Monday Night 3000'
Tuesday Morning 3000'
Tuesday Afternoon 4000'
Stevens Pass Elevation
Sunday Evening* 2500'
Sunday Night* 2000'
Monday Morning* 2000'
Monday Afternoon* 4000'
Monday Evening 3000'
Monday Night 2500'
Tuesday Morning 2500'
Tuesday Afternoon 3500'
Snoqualmie Pass Elevation
Sunday Evening* 3000'
Sunday Night* 2000'
Monday Morning* 3000'
Monday Afternoon* 4500'
Monday Evening 3000'
Monday Night 2500'
Tuesday Morning 2500'
Tuesday Afternoon 3500'
East North Elevation
Sunday Evening* 2000'
Sunday Night* 2000'
Monday Morning* 2000'
Monday Afternoon* 3500'
Monday Evening 3000'
Monday Night 2500'
Tuesday Morning 2000'
Tuesday Afternoon 3000'
East Central Elevation
Sunday Evening* 2500'
Sunday Night* 2000'
Monday Morning* 2000'
Monday Afternoon* 3500'
Monday Evening 3000'
Monday Night 2500'
Tuesday Morning 2500'
Tuesday Afternoon 3500'
East South Elevation
Sunday Evening* 2500'
Sunday Night* 2000'
Monday Morning* 2000'
Monday Afternoon* 4500'
Monday Evening 3500'
Monday Night 3000'
Tuesday Morning 3000'
Tuesday Afternoon 4500'
Mt. Hood Elevation
Sunday Evening* 3500'
Sunday Night* 3000'
Monday Morning* 3000'
Monday Afternoon* 4500'
Monday Evening 4000'
Monday Night 4000'
Tuesday Morning 4000'
Tuesday Afternoon 5500'

Issued: 2:09 PM PST Sunday, December 27, 2020

5000' Temperatures (°F)

Sunday Night Monday
Max / Min Max / Min
Olympics 28 / 26 33 / 26
West North 27 / 25 30 / 23
West Central 25 / 24 30 / 25
West South 28 / 26 37 / 26
Stevens Pass 22 / 19 33 / 18
Snoqualmie Pass 23 / 21 31 / 21
East North 21 / 18 30 / 19
East Central 22 / 19 33 / 20
East South 22 / 20 37 / 21
Mt. Hood 27 / 25 38 / 26
Olympics 5000' Temperature Forecast
(Max / Min)
Sunday Night 28 / 26
Monday 33 / 26
West North 5000' Temperature Forecast
(Max / Min)
Sunday Night 27 / 25
Monday 30 / 23
West Central 5000' Temperature Forecast
(Max / Min)
Sunday Night 25 / 24
Monday 30 / 25
West South 5000' Temperature Forecast
(Max / Min)
Sunday Night 28 / 26
Monday 37 / 26
Stevens Pass 5000' Temperature Forecast
(Max / Min)
Sunday Night 22 / 19
Monday 33 / 18
Snoqualmie Pass 5000' Temperature Forecast
(Max / Min)
Sunday Night 23 / 21
Monday 31 / 21
East North 5000' Temperature Forecast
(Max / Min)
Sunday Night 21 / 18
Monday 30 / 19
East Central 5000' Temperature Forecast
(Max / Min)
Sunday Night 22 / 19
Monday 33 / 20
East South 5000' Temperature Forecast
(Max / Min)
Sunday Night 22 / 20
Monday 37 / 21
Mt. Hood 5000' Temperature Forecast
(Max / Min)
Sunday Night 27 / 25
Monday 38 / 26

Issued: 2:09 PM PST Sunday, December 27, 2020

Ridgeline Winds (mph)

Sunday Evening Sunday Night Monday Morning Monday Afternoon
Olympics S 0-10 SSW 0-10 NW 0-10 WNW 0-10
West North S 0-10 SSW 0-10 W 0-10 WNW 0-10
West Central SE 5-15 SE 5-15 SE 0-10 NW 0-10
West South ESE 0-10 SE 0-10 W 0-10 NNW 0-10
Stevens Pass SE 5-15 SSE 5-15 SSE 0-10 WNW 0-10
Snoqualmie Pass ESE 5-15 ESE 5-15 ESE 0-10 NW 5-15
East North S 5-15 S 5-15 WSW 0-10 WNW 5-15
East Central S 10-20 S 5-15 SW 5-15 WNW 5-15
East South SE 5-15 SSE 5-15 SSW 0-10 WNW 0-10
Mt. Hood S 10-20 S 10-20 S 5-15 W 0-10
Olympics Ridgeline Winds (mph)
Sunday Evening S 0-10
Sunday Night SSW 0-10
Monday Morning NW 0-10
Monday Afternoon WNW 0-10
West North Ridgeline Winds (mph)
Sunday Evening S 0-10
Sunday Night SSW 0-10
Monday Morning W 0-10
Monday Afternoon WNW 0-10
West Central Ridgeline Winds (mph)
Sunday Evening SE 5-15
Sunday Night SE 5-15
Monday Morning SE 0-10
Monday Afternoon NW 0-10
West South Ridgeline Winds (mph)
Sunday Evening ESE 0-10
Sunday Night SE 0-10
Monday Morning W 0-10
Monday Afternoon NNW 0-10
Stevens Pass Ridgeline Winds (mph)
Sunday Evening SE 5-15
Sunday Night SSE 5-15
Monday Morning SSE 0-10
Monday Afternoon WNW 0-10
Snoqualmie Pass Ridgeline Winds (mph)
Sunday Evening ESE 5-15
Sunday Night ESE 5-15
Monday Morning ESE 0-10
Monday Afternoon NW 5-15
East North Ridgeline Winds (mph)
Sunday Evening S 5-15
Sunday Night S 5-15
Monday Morning WSW 0-10
Monday Afternoon WNW 5-15
East Central Ridgeline Winds (mph)
Sunday Evening S 10-20
Sunday Night S 5-15
Monday Morning SW 5-15
Monday Afternoon WNW 5-15
East South Ridgeline Winds (mph)
Sunday Evening SE 5-15
Sunday Night SSE 5-15
Monday Morning SSW 0-10
Monday Afternoon WNW 0-10
Mt. Hood Ridgeline Winds (mph)
Sunday Evening S 10-20
Sunday Night S 10-20
Monday Morning S 5-15
Monday Afternoon W 0-10

Issued: 2:09 PM PST Sunday, December 27, 2020

Extended Weather Synopsis

Things get a lot more active in the extended period. Tuesday night, an initial frontal system skirting over the retreating ridge brings a wave of light rain and snow to Washington State. With cool air in place, most of this is expected to fall as snow. The next system, hot on the heels of the first, lifts a warm front northward across the region with moderate rain and snow expected and snow levels bumping up to above 5000 ft for the Olympics. A sizeable cold air pool east of the Cascades combined with moderate E flow should keep the passes as snow. The occluded low sends a cold front into the region late Wednesday, with heavy rain and snow. A deep trough settles into the region Wednesday night and Thursday with generally moderate snow shower activity decreasing and becoming light by Thursday. Lower pressure offshore continues to drive diminishing E flow through the mountain gaps. We'll have to watch the potential for secondary lows to develop around the trough.

Extended Snow Level (ft)

Tuesday Night* Wednesday * Wednesday Night* Thursday *
West North 2000' 3000' 2500' 2500'
Snoqualmie Pass 2000' 3000' 2500' 2500'
Mt. Hood 4000' 4500' 3500' 3500'
West North Elevation
Tuesday Night* 2000'
Wednesday * 3000'
Wednesday Night* 2500'
Thursday * 2500'
Snoqualmie Pass Elevation
Tuesday Night* 2000'
Wednesday * 3000'
Wednesday Night* 2500'
Thursday * 2500'
Mt. Hood Elevation
Tuesday Night* 4000'
Wednesday * 4500'
Wednesday Night* 3500'
Thursday * 3500'

Jump to: Weather Forecast I Precipitation I Snow Level I 5000' Temps I Ridgeline Winds I Extended Weather

Previous forecast from Dec 27, 2020

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).

The label LT, is shorthand for ‘less than’.