Issued: 2:20 PM PST Saturday, December 12, 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 first in a series of storms arrives late Saturday night into Sunday morning. Out ahead of it, clouds increase Saturday evening as milder air arrives to the west of the Cascade Crest, brought in by increasing southerly flow aloft. Easterly low-level flow peaks in the moderate range overnight, driven by an entrenched cold air pool creating high pressure at the surface east of the Cascade Crest and a deep upper-level trough offshore. Expect some strong winds in exposed locations in the Snoqualmie, Crystal, White Pass, and east Central Cascades. This offshore flow should insulate most of the Cascades from any warming. Thus, snow levels will be well below pass level and the Cascade foothills may start off as snow when the precipitation arrives late Saturday night or early Sunday.

The frontal passes Sunday morning, switching flow to the SW as E flow becomes light. Expect snow to be generally in the light to moderate range on Sunday, but Paradise and Mt. Hood area likely to see heavier snowfall. Winds will also be more sustained at Mt Hood.

The trough moves onshore Sunday night and slides east on Monday with lighter snow shower activity diminishing throughout with cool air remaining over the region.

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
Saturday Night Clouds lowering and thickening in the evening with light rain and snow developing in the early morning hours. Mild. Precipitation could start as a rain/snow mix at Hurricane Ridge. Moderate winds.
Sunday Decreasing light rain and snow showers. Gradual cooling. Moderate ridgeline winds becoming light.
Saturday Night Increasing clouds, lowering and thickening after midnight. Ridgeline winds increasing into the moderate range after midnight.
Sunday Moderate snow. Decreasing moderate winds.
Saturday Night Increasing clouds, lowering and thickening after midnight with a chance of light snow developing late. Ridgeline winds increasing into the moderate range after midnight.
Sunday Light to moderate snow becoming showery. Decreasing moderate winds becoming light late in the day.
Saturday Night Increasing clouds, lowering and thickening after midnight with light snow developing late. Increasing light ridgeline winds with gusts into the moderate range.
Sunday Heavy snow (Paradise) with light to moderate snow (Crystal/White Pass). Light ridgeline winds with moderate gusts.
Saturday Night Increasing clouds, lowering and thickening after midnight with light snow developing late. Cold. Moderate ridgeline and E pass-level winds with strong gusts.
Sunday Light snow becoming showery. Decreasing light ridgeline and E pass-level winds.
Saturday Night Increasing clouds, lowering and thickening after midnight with light snow developing late. Cold. Moderate ridgeline and E pass-level winds with strong gusts.
Sunday Increasing moderate snow. Decreasing moderate ridgeline and E pass-level winds, becoming light.
Saturday Night Clear in the evening, then increasing clouds. Cold. Increasing light to moderate ridgeline winds.
Sunday Light snow becoming showery. Light ridgeline winds with moderate gusts.
Saturday Night Increasing clouds, lowering and thickening after midnight with light snow developing late. Cold. Moderate ridgeline winds with strong gusts.
Sunday Light snow becoming showery. Moderate ridgeline winds becoming light.
Saturday Night Increasing clouds, lowering and thickening after midnight with light snow developing late. Cold. Light to moderate ridgeline with some strong gusts.
Sunday Light snow becoming showery. Light ridgeline winds.
Saturday Night Increasing clouds, lowering and thickening after midnight with light to moderate snow developing late. Cool. Increasing moderate ridgeline winds with strong gusts.
Sunday Periods of moderate to heavy snow. Moderate ridgeline winds with strong gusts.

Issued: 2:20 PM PST Saturday, December 12, 2020

Precipitation (in)

Saturday Night Sunday Sunday Night Monday
4 pm - 4 am 4 am - 4 pm 4 pm - 4 am 4 am - 4 pm
Hurricane Ridge LT 0.25 0.25 - 0.50 LT 0.10 LT 0.10
Mt Baker Ski Area 0 0.50 - 0.75 0.25 LT 0.10
Mt. Loop - Barlow Pass 0 0.25 - 0.50 0.50 LT 0.25
Stevens Pass 0 0.25 0.25 - 0.50 0.25
Snoqualmie Pass LT 0.10 0.25 - 0.50 0.50 0.25
Crystal Mt LT 0.10 0.25 LT 0.10 LT 0.10
Paradise LT 0.25 0.75 -1.00 0.50 LT 0.25
White Pass LT 0.10 0.25 - 0.50 0.25 LT 0.10
Washington Pass 0 LT 0.10 LT 0.10 LT 0.10
Mission Ridge 0 LT 0.25 LT 0.10 0
Salmon la Sac - Gallagher Head LT 0.10 0.25 LT 0.25 LT 0.10
Tieton River - Darland Mt. LT 0.10 0.25 LT 0.10 0
Mt Hood Meadows 0.25 0.75 -1.00 0.75 LT 0.25
Timberline 0.25 1.00 0.75 -1.00 LT 0.25
Hurricane Ridge Precipitation (in)
Saturday Night LT 0.25
Sunday 0.25 - 0.50
Sunday Night LT 0.10
Monday LT 0.10
Mt Baker Ski Area Precipitation (in)
Saturday Night 0
Sunday 0.50 - 0.75
Sunday Night 0.25
Monday LT 0.10
Mt. Loop - Barlow Pass Precipitation (in)
Saturday Night 0
Sunday 0.25 - 0.50
Sunday Night 0.50
Monday LT 0.25
Stevens Pass Precipitation (in)
Saturday Night 0
Sunday 0.25
Sunday Night 0.25 - 0.50
Monday 0.25
Snoqualmie Pass Precipitation (in)
Saturday Night LT 0.10
Sunday 0.25 - 0.50
Sunday Night 0.50
Monday 0.25
Crystal Mt Precipitation (in)
Saturday Night LT 0.10
Sunday 0.25
Sunday Night LT 0.10
Monday LT 0.10
Paradise Precipitation (in)
Saturday Night LT 0.25
Sunday 0.75 -1.00
Sunday Night 0.50
Monday LT 0.25
White Pass Precipitation (in)
Saturday Night LT 0.10
Sunday 0.25 - 0.50
Sunday Night 0.25
Monday LT 0.10
Washington Pass Precipitation (in)
Saturday Night 0
Sunday LT 0.10
Sunday Night LT 0.10
Monday LT 0.10
Mission Ridge Precipitation (in)
Saturday Night 0
Sunday LT 0.25
Sunday Night LT 0.10
Monday 0
Salmon la Sac - Gallagher Head Precipitation (in)
Saturday Night LT 0.10
Sunday 0.25
Sunday Night LT 0.25
Monday LT 0.10
Tieton River - Darland Mt. Precipitation (in)
Saturday Night LT 0.10
Sunday 0.25
Sunday Night LT 0.10
Monday 0
Mt Hood Meadows Precipitation (in)
Saturday Night 0.25
Sunday 0.75 -1.00
Sunday Night 0.75
Monday LT 0.25
Timberline Precipitation (in)
Saturday Night 0.25
Sunday 1.00
Sunday Night 0.75 -1.00
Monday LT 0.25

Issued: 2:20 PM PST Saturday, December 12, 2020

Snow Level (ft)

Saturday Evening* Saturday Night* Sunday Morning* Sunday Afternoon* Sunday Evening* Sunday Night Monday Morning Monday Afternoon
Olympics 6500' 5000' 4000' 4000' 3500' 3000' 3000' 3000'
West North 2500' 2000' 2000' 2500' 2500' 2500' 2500' 2500'
West Central 2500' 2000' 2000' 2500' 2500' 2500' 2500' 2500'
West South 2500' 2000' 2500' 3000' 3000' 3000' 2500' 3000'
Stevens Pass 1500' 1000' 1000' 2000' 2000' 2000' 2000' 2500'
Snoqualmie Pass 1500' 1000' 1500' 2000' 2500' 2500' 2500' 2500'
East North 1000' 0 500' 1500' 1500' 1500' 1500' 2000'
East Central 1500' 1000' 1000' 2000' 2000' 2000' 2000' 2500'
East South 1500' 1000' 1500' 2500' 2500' 3000' 3000' 3000'
Mt. Hood 2500' 2500' 3500' 3500' 3000' 3000' 3000' 3000'
Olympics Elevation
Saturday Evening* 6500'
Saturday Night* 5000'
Sunday Morning* 4000'
Sunday Afternoon* 4000'
Sunday Evening* 3500'
Sunday Night 3000'
Monday Morning 3000'
Monday Afternoon 3000'
West North Elevation
Saturday Evening* 2500'
Saturday Night* 2000'
Sunday Morning* 2000'
Sunday Afternoon* 2500'
Sunday Evening* 2500'
Sunday Night 2500'
Monday Morning 2500'
Monday Afternoon 2500'
West Central Elevation
Saturday Evening* 2500'
Saturday Night* 2000'
Sunday Morning* 2000'
Sunday Afternoon* 2500'
Sunday Evening* 2500'
Sunday Night 2500'
Monday Morning 2500'
Monday Afternoon 2500'
West South Elevation
Saturday Evening* 2500'
Saturday Night* 2000'
Sunday Morning* 2500'
Sunday Afternoon* 3000'
Sunday Evening* 3000'
Sunday Night 3000'
Monday Morning 2500'
Monday Afternoon 3000'
Stevens Pass Elevation
Saturday Evening* 1500'
Saturday Night* 1000'
Sunday Morning* 1000'
Sunday Afternoon* 2000'
Sunday Evening* 2000'
Sunday Night 2000'
Monday Morning 2000'
Monday Afternoon 2500'
Snoqualmie Pass Elevation
Saturday Evening* 1500'
Saturday Night* 1000'
Sunday Morning* 1500'
Sunday Afternoon* 2000'
Sunday Evening* 2500'
Sunday Night 2500'
Monday Morning 2500'
Monday Afternoon 2500'
East North Elevation
Saturday Evening* 1000'
Saturday Night* 0'
Sunday Morning* 500'
Sunday Afternoon* 1500'
Sunday Evening* 1500'
Sunday Night 1500'
Monday Morning 1500'
Monday Afternoon 2000'
East Central Elevation
Saturday Evening* 1500'
Saturday Night* 1000'
Sunday Morning* 1000'
Sunday Afternoon* 2000'
Sunday Evening* 2000'
Sunday Night 2000'
Monday Morning 2000'
Monday Afternoon 2500'
East South Elevation
Saturday Evening* 1500'
Saturday Night* 1000'
Sunday Morning* 1500'
Sunday Afternoon* 2500'
Sunday Evening* 2500'
Sunday Night 3000'
Monday Morning 3000'
Monday Afternoon 3000'
Mt. Hood Elevation
Saturday Evening* 2500'
Saturday Night* 2500'
Sunday Morning* 3500'
Sunday Afternoon* 3500'
Sunday Evening* 3000'
Sunday Night 3000'
Monday Morning 3000'
Monday Afternoon 3000'

Issued: 2:20 PM PST Saturday, December 12, 2020

5000' Temperatures (°F)

Saturday Night Sunday
Max / Min Max / Min
Olympics 34 / 28 31 / 28
West North 28 / 25 28 / 24
West Central 23 / 20 26 / 20
West South 29 / 25 30 / 27
Stevens Pass 19 / 16 23 / 18
Snoqualmie Pass 19 / 17 24 / 18
East North 15 / 14 20 / 14
East Central 18 / 16 23 / 17
East South 19 / 15 28 / 18
Mt. Hood 26 / 22 31 / 26
Olympics 5000' Temperature Forecast
(Max / Min)
Saturday Night 34 / 28
Sunday 31 / 28
West North 5000' Temperature Forecast
(Max / Min)
Saturday Night 28 / 25
Sunday 28 / 24
West Central 5000' Temperature Forecast
(Max / Min)
Saturday Night 23 / 20
Sunday 26 / 20
West South 5000' Temperature Forecast
(Max / Min)
Saturday Night 29 / 25
Sunday 30 / 27
Stevens Pass 5000' Temperature Forecast
(Max / Min)
Saturday Night 19 / 16
Sunday 23 / 18
Snoqualmie Pass 5000' Temperature Forecast
(Max / Min)
Saturday Night 19 / 17
Sunday 24 / 18
East North 5000' Temperature Forecast
(Max / Min)
Saturday Night 15 / 14
Sunday 20 / 14
East Central 5000' Temperature Forecast
(Max / Min)
Saturday Night 18 / 16
Sunday 23 / 17
East South 5000' Temperature Forecast
(Max / Min)
Saturday Night 19 / 15
Sunday 28 / 18
Mt. Hood 5000' Temperature Forecast
(Max / Min)
Saturday Night 26 / 22
Sunday 31 / 26

Issued: 2:20 PM PST Saturday, December 12, 2020

Ridgeline Winds (mph)

Saturday Evening Saturday Night Sunday Morning Sunday Afternoon
Olympics S 10-20 S 15-25 SSW 10-20 WSW 5-15
West North SE 5-15 SSE 10-20 S 15-25 SSW 10-20
West Central SE 15-25 SE 15-25 SE 15-25 SSE 5-15
West South SE 5-15 SSE 5-15 S 5-15 SSW 5-15
Stevens Pass SE 10-20 SE 10-20 SE 5-15 S 0-10
Snoqualmie Pass ESE 15-25 ESE 15-25 ESE 10-20 SSE 5-15
East North SE 5-15 SE 10-20 SSE 5-15 SSW 5-15
East Central SSE 10-20 S 15-25 S 10-20 SW 10-20
East South SSE 10-20 SSE 10-20 S 5-15 SW 5-15
Mt. Hood SSW 10-20 SSW 20-30 SW 20-30 WSW 25-35
Olympics Ridgeline Winds (mph)
Saturday Evening S 10-20
Saturday Night S 15-25
Sunday Morning SSW 10-20
Sunday Afternoon WSW 5-15
West North Ridgeline Winds (mph)
Saturday Evening SE 5-15
Saturday Night SSE 10-20
Sunday Morning S 15-25
Sunday Afternoon SSW 10-20
West Central Ridgeline Winds (mph)
Saturday Evening SE 15-25
Saturday Night SE 15-25
Sunday Morning SE 15-25
Sunday Afternoon SSE 5-15
West South Ridgeline Winds (mph)
Saturday Evening SE 5-15
Saturday Night SSE 5-15
Sunday Morning S 5-15
Sunday Afternoon SSW 5-15
Stevens Pass Ridgeline Winds (mph)
Saturday Evening SE 10-20
Saturday Night SE 10-20
Sunday Morning SE 5-15
Sunday Afternoon S 0-10
Snoqualmie Pass Ridgeline Winds (mph)
Saturday Evening ESE 15-25
Saturday Night ESE 15-25
Sunday Morning ESE 10-20
Sunday Afternoon SSE 5-15
East North Ridgeline Winds (mph)
Saturday Evening SE 5-15
Saturday Night SE 10-20
Sunday Morning SSE 5-15
Sunday Afternoon SSW 5-15
East Central Ridgeline Winds (mph)
Saturday Evening SSE 10-20
Saturday Night S 15-25
Sunday Morning S 10-20
Sunday Afternoon SW 10-20
East South Ridgeline Winds (mph)
Saturday Evening SSE 10-20
Saturday Night SSE 10-20
Sunday Morning S 5-15
Sunday Afternoon SW 5-15
Mt. Hood Ridgeline Winds (mph)
Saturday Evening SSW 10-20
Saturday Night SSW 20-30
Sunday Morning SW 20-30
Sunday Afternoon WSW 25-35

Issued: 2:20 PM PST Saturday, December 12, 2020

Extended Weather Synopsis

With snow flurry activity winding down as the previous trough moves east, the next system moves into the nearshore waters Monday night. Like Sunday's system, the frontal system is attached to a deep low tracking toward the Alaska Panhandle. This system should bring some moderate snowfall, on Tuesday. Post-frontal snow showers may be lighter and shorter-lived this time as limited moisture continues to spill into the region over a subtle ridge pops that up behind the front Tuesday night. Another significant system tracks more directly toward the Pacific Northwest and is expected to arrive Wednesday night and could be a major snow producer.

Extended Snow Level (ft)

Monday Night* Tuesday * Tuesday Night Wednesday *
West North 1500' 2000' 2500' 3000'
Snoqualmie Pass 1500' 2000' 3000' 3500'
Mt. Hood 3000' 3500' 4500' 5000'
West North Elevation
Monday Night* 1500'
Tuesday * 2000'
Tuesday Night 2500'
Wednesday * 3000'
Snoqualmie Pass Elevation
Monday Night* 1500'
Tuesday * 2000'
Tuesday Night 3000'
Wednesday * 3500'
Mt. Hood Elevation
Monday Night* 3000'
Tuesday * 3500'
Tuesday Night 4500'
Wednesday * 5000'

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

Previous forecast from Dec 12, 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’.