Issued: 2:13 PM PST Friday, December 17, 2021
by Dennis D'Amico

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

Weather Synopsis

After a benign day with increasing high clouds, a major winter storm is on tap for the weekend. A low pressure system curling towards the central British Columbia coast will spread warm frontal moisture inland tonight. Forecast models have trended heavier with this first wave of moisture overnight.  With cold air entrenched in place, snow levels will be slow to rise over the Cascades tonight. The warm frontal precipitation will lift northwards Saturday morning, potentially relaxing precipitation rates south of Snoqualmie Pass during the morning hours. The trailing cold front will slowly sag south Saturday afternoon, bringing extreme SW alpine winds and heavy precipitation to most areas. There's still wild divergence in precipitation amounts from Stevens Pass and southward regarding how heavy precipitation is during the day on Saturday. On top of that, warm air overrunning cold air entrenched in the Cascades opens the door for a wintry mix, including freezing rain, in some locations. The west-side south of Hwy 2 and Snoqualmie and White Passes may a mix late morning while the east slopes of the Cascades near and south of I-90 may see a wintry mix in the afternoon to early evening Saturday. The north Cascades and likely Stevens Pass will stay snow with a much more muted warming trend. Mt Hood will be on the warm side for this system with 6000-7000' snow levels Saturday.

The front will slowly sag south Saturday evening and become a stationary feature across the Columbia River gap by early Sunday morning. Showers should quickly end from north to south overnight Saturday for the Washington Cascades and Olympics as snow levels fall behind the front. The frontal boundary may stay draped over the Washington/Oregon border on Sunday, where locally moderate to heavy precipitation is possible for Mt. Hood. Much drier air will filter into closer to the Canadain border on Sunday.  

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
Friday Night Light rain and snow developing and becoming moderate after midnight. Strong winds developing overnight.
Saturday Heavy rain and snow in the morning becoming scattered rain and snow showers in the afternoon. Strong to extreme ridgeline winds in the morning, easing in the afternoon. Cooling trend in the afternoon.
Friday Night Light rain and snow developing and becoming moderate after midnight. Strong winds developing overnight.
Saturday Heavy rain and snow in the morning becoming scattered rain and snow showers late in the afternoon. Strong to extreme ridgeline winds in the morning, easing in the afternoon. Cooling trend late.
Friday Night Light rain and snow developing and becoming moderate after midnight. Strong winds developing overnight.
Saturday Heavy rain and snow. Strong to extreme ridgeline winds.
Friday Night Cloudy, then light rain and snow developing after midnight. Strong winds developing late.
Saturday Light rain and snow becoming moderate to locally heavy in the afternoon. Strong to extreme ridgeline winds developing during the day. Warming trend.
Friday Night Cloudy, then light rain and snow developing after midnight and increasing late. Light east winds at Pass level becoming moderate after midnight.
Saturday Moderate to occasionally heavy rain and snow. Strong to extreme ridgeline west winds developing during the day. Moderate east winds at Pass level becoming west in the afternoon. Slight chance of freezing rain late. Slight warming trend.
Friday Night Cloudy, then light rain and snow developing after midnight and increasing late. Light east winds at Pass level becoming moderate after midnight.
Saturday Light to moderate rain and snow becoming heavy in the afternoon. Strong to extreme ridgeline west winds developing during the day. Moderate east winds at Pass level becoming west in the afternoon. Chance for freezing rain from mid-morning through early afternoon. Warming trend.
Friday Night Cloudy, then light rain and snow developing after midnight and increasing late.
Saturday Moderate to occasionally heavy snow. Strong ridgeline winds.
Friday Night Cloudy, then light rain and snow developing after midnight. Strong winds developing late.
Saturday Light to moderate snow increasing in the afternoon. Chance of freezing rain late in the day. Strong to extreme ridgeline winds developing. Slight warming trend.
Friday Night Cloudy, then light rain and snow developing after midnight.
Saturday Light to occasionally moderate snow increasing in the afternoon. Chance of freezing rain in the afternoon.Strong to extreme ridgeline winds developing. Slight warming trend.
Friday Night Cloudy, then light rain and snow developing after midnight.
Saturday Light rain and snow increasing in the afternoon. Strong to extreme winds, especially in the alpine. Warming trend.

Issued: 2:13 PM PST Friday, December 17, 2021

Precipitation (in)

Friday Night Saturday Saturday Night Sunday
4 pm - 4 am 4 am - 4 pm 4 pm - 4 am 4 am - 4 pm
Hurricane Ridge 0.50 - 0.75 1.50 LT 0.10 0
Mt Baker Ski Area 0.75 1.50 - 2.00 LT 0.25 0
Mt. Loop - Barlow Pass 0.50 2.00 0.50 0
Stevens Pass 0.25 - 0.50 1.00 - 1.50 0.50 0
Snoqualmie Pass 0.25 - 0.50 1.00 0.75 0
Crystal Mt LT 0.25 0.50 - 0.75 0.50 LT 0.10
Paradise 0.50 1.00 - 1.50 0.75 LT 0.25
White Pass 0.25 0.50 0.75 -1.00 LT 0.25
Washington Pass 0.25 1.00 - 1.50 0.25 - 0.50 0
Mission Ridge LT 0.25 0.25 LT 0.25 LT 0.10
Salmon la Sac - Gallagher Head 0.25 0.75 0.25 - 0.50 0
Tieton River - Darland Mt. LT 0.25 0.25 - 0.50 0.50 LT 0.25
Mt Hood Meadows LT 0.25 0.50 1.00 1.00
Timberline 0.25 0.50 1.00 - 1.50 1.00
Hurricane Ridge Precipitation (in)
Friday Night 0.50 - 0.75
Saturday 1.50
Saturday Night LT 0.10
Sunday 0
Mt Baker Ski Area Precipitation (in)
Friday Night 0.75
Saturday 1.50 - 2.00
Saturday Night LT 0.25
Sunday 0
Mt. Loop - Barlow Pass Precipitation (in)
Friday Night 0.50
Saturday 2.00
Saturday Night 0.50
Sunday 0
Stevens Pass Precipitation (in)
Friday Night 0.25 - 0.50
Saturday 1.00 - 1.50
Saturday Night 0.50
Sunday 0
Snoqualmie Pass Precipitation (in)
Friday Night 0.25 - 0.50
Saturday 1.00
Saturday Night 0.75
Sunday 0
Crystal Mt Precipitation (in)
Friday Night LT 0.25
Saturday 0.50 - 0.75
Saturday Night 0.50
Sunday LT 0.10
Paradise Precipitation (in)
Friday Night 0.50
Saturday 1.00 - 1.50
Saturday Night 0.75
Sunday LT 0.25
White Pass Precipitation (in)
Friday Night 0.25
Saturday 0.50
Saturday Night 0.75 -1.00
Sunday LT 0.25
Washington Pass Precipitation (in)
Friday Night 0.25
Saturday 1.00 - 1.50
Saturday Night 0.25 - 0.50
Sunday 0
Mission Ridge Precipitation (in)
Friday Night LT 0.25
Saturday 0.25
Saturday Night LT 0.25
Sunday LT 0.10
Salmon la Sac - Gallagher Head Precipitation (in)
Friday Night 0.25
Saturday 0.75
Saturday Night 0.25 - 0.50
Sunday 0
Tieton River - Darland Mt. Precipitation (in)
Friday Night LT 0.25
Saturday 0.25 - 0.50
Saturday Night 0.50
Sunday LT 0.25
Mt Hood Meadows Precipitation (in)
Friday Night LT 0.25
Saturday 0.50
Saturday Night 1.00
Sunday 1.00
Timberline Precipitation (in)
Friday Night 0.25
Saturday 0.50
Saturday Night 1.00 - 1.50
Sunday 1.00

Issued: 2:13 PM PST Friday, December 17, 2021

Snow Level (ft)

Friday Evening* Friday Night* Saturday Morning* Saturday Afternoon Saturday Evening Saturday Night Sunday Morning Sunday Afternoon
Olympics 2000' 2500' 5000' 3500' 2000' 1500' 1000' 2000'
West North 1000' 1500' 2000' 3500' 2000' 1000' 500' 1500'
West Central 1000' 1500' 3000' 4500' 2500' 1000' 1000' 2000'
West South 1500' 2000' 3500' 5000' 3000' 2000' 1500' 2500'
Stevens Pass 500' 1000' 1500' 4000' 2500' 1000' 500' 2000'
Snoqualmie Pass 1000' 1500' 3000' 4500' 3000' 1500' 1000' 2500'
East North 0 0 1000' 1000' 1500' 0 0 2000'
East Central 0 0 1000' 1500' 2000' 1000' 500' 2000'
East South 1000' 1500' 2500' 5000' 3500' 2000' 2500' 2500'
Mt. Hood 3000' 2500' 6500' 7000' 4500' 4500' 4500' 4000'
Olympics Elevation
Friday Evening* 2000'
Friday Night* 2500'
Saturday Morning* 5000'
Saturday Afternoon 3500'
Saturday Evening 2000'
Saturday Night 1500'
Sunday Morning 1000'
Sunday Afternoon 2000'
West North Elevation
Friday Evening* 1000'
Friday Night* 1500'
Saturday Morning* 2000'
Saturday Afternoon 3500'
Saturday Evening 2000'
Saturday Night 1000'
Sunday Morning 500'
Sunday Afternoon 1500'
West Central Elevation
Friday Evening* 1000'
Friday Night* 1500'
Saturday Morning* 3000'
Saturday Afternoon 4500'
Saturday Evening 2500'
Saturday Night 1000'
Sunday Morning 1000'
Sunday Afternoon 2000'
West South Elevation
Friday Evening* 1500'
Friday Night* 2000'
Saturday Morning* 3500'
Saturday Afternoon 5000'
Saturday Evening 3000'
Saturday Night 2000'
Sunday Morning 1500'
Sunday Afternoon 2500'
Stevens Pass Elevation
Friday Evening* 500'
Friday Night* 1000'
Saturday Morning* 1500'
Saturday Afternoon 4000'
Saturday Evening 2500'
Saturday Night 1000'
Sunday Morning 500'
Sunday Afternoon 2000'
Snoqualmie Pass Elevation
Friday Evening* 1000'
Friday Night* 1500'
Saturday Morning* 3000'
Saturday Afternoon 4500'
Saturday Evening 3000'
Saturday Night 1500'
Sunday Morning 1000'
Sunday Afternoon 2500'
East North Elevation
Friday Evening* 0'
Friday Night* 0'
Saturday Morning* 1000'
Saturday Afternoon 1000'
Saturday Evening 1500'
Saturday Night 0'
Sunday Morning 0'
Sunday Afternoon 2000'
East Central Elevation
Friday Evening* 0'
Friday Night* 0'
Saturday Morning* 1000'
Saturday Afternoon 1500'
Saturday Evening 2000'
Saturday Night 1000'
Sunday Morning 500'
Sunday Afternoon 2000'
East South Elevation
Friday Evening* 1000'
Friday Night* 1500'
Saturday Morning* 2500'
Saturday Afternoon 5000'
Saturday Evening 3500'
Saturday Night 2000'
Sunday Morning 2500'
Sunday Afternoon 2500'
Mt. Hood Elevation
Friday Evening* 3000'
Friday Night* 2500'
Saturday Morning* 6500'
Saturday Afternoon 7000'
Saturday Evening 4500'
Saturday Night 4500'
Sunday Morning 4500'
Sunday Afternoon 4000'

Issued: 2:13 PM PST Friday, December 17, 2021

5000' Temperatures (°F)

Friday Night Saturday
Max / Min Max / Min
Olympics 33 / 24 33 / 25
West North 28 / 20 31 / 24
West Central 28 / 21 33 / 26
West South 30 / 23 33 / 28
Stevens Pass 25 / 19 33 / 25
Snoqualmie Pass 24 / 19 34 / 26
East North 17 / 13 27 / 18
East Central 22 / 19 33 / 23
East South 29 / 23 34 / 30
Mt. Hood 31 / 25 36 / 32
Olympics 5000' Temperature Forecast
(Max / Min)
Friday Night 33 / 24
Saturday 33 / 25
West North 5000' Temperature Forecast
(Max / Min)
Friday Night 28 / 20
Saturday 31 / 24
West Central 5000' Temperature Forecast
(Max / Min)
Friday Night 28 / 21
Saturday 33 / 26
West South 5000' Temperature Forecast
(Max / Min)
Friday Night 30 / 23
Saturday 33 / 28
Stevens Pass 5000' Temperature Forecast
(Max / Min)
Friday Night 25 / 19
Saturday 33 / 25
Snoqualmie Pass 5000' Temperature Forecast
(Max / Min)
Friday Night 24 / 19
Saturday 34 / 26
East North 5000' Temperature Forecast
(Max / Min)
Friday Night 17 / 13
Saturday 27 / 18
East Central 5000' Temperature Forecast
(Max / Min)
Friday Night 22 / 19
Saturday 33 / 23
East South 5000' Temperature Forecast
(Max / Min)
Friday Night 29 / 23
Saturday 34 / 30
Mt. Hood 5000' Temperature Forecast
(Max / Min)
Friday Night 31 / 25
Saturday 36 / 32

Issued: 2:13 PM PST Friday, December 17, 2021

Ridgeline Winds (mph)

Friday Evening Friday Night Saturday Morning Saturday Afternoon
Olympics S 10-20 SW 25-35 SW 35-50 WSW 15-25
West North S 15-25 SSW 25-35 SSW 40-55 WSW 15-25
West Central SW 10-20 SW 20-30 SW 40-55 WSW 25-35
West South SW 10-20 SSW 20-30 SW 25-35 SW 40-55
Stevens Pass SW 5-15 SSE 5-15 SW 25-35 SW 30-40
Snoqualmie Pass SW 5-15 SSE 5-15 SW 25-35 SW 35-50
East North SW 10-20 SW 10-20 SW 25-35 WSW 20-30
East Central SW 5-15 SSW 15-25 SW 20-30 SW 40-55
East South SSW 5-15 SW 10-20 WSW 25-35 WSW 40-55
Mt. Hood SW 10-20 WSW 20-30 WSW 25-35 WSW 40-55
Olympics Ridgeline Winds (mph)
Friday Evening S 10-20
Friday Night SW 25-35
Saturday Morning SW 35-50
Saturday Afternoon WSW 15-25
West North Ridgeline Winds (mph)
Friday Evening S 15-25
Friday Night SSW 25-35
Saturday Morning SSW 40-55
Saturday Afternoon WSW 15-25
West Central Ridgeline Winds (mph)
Friday Evening SW 10-20
Friday Night SW 20-30
Saturday Morning SW 40-55
Saturday Afternoon WSW 25-35
West South Ridgeline Winds (mph)
Friday Evening SW 10-20
Friday Night SSW 20-30
Saturday Morning SW 25-35
Saturday Afternoon SW 40-55
Stevens Pass Ridgeline Winds (mph)
Friday Evening SW 5-15
Friday Night SSE 5-15
Saturday Morning SW 25-35
Saturday Afternoon SW 30-40
Snoqualmie Pass Ridgeline Winds (mph)
Friday Evening SW 5-15
Friday Night SSE 5-15
Saturday Morning SW 25-35
Saturday Afternoon SW 35-50
East North Ridgeline Winds (mph)
Friday Evening SW 10-20
Friday Night SW 10-20
Saturday Morning SW 25-35
Saturday Afternoon WSW 20-30
East Central Ridgeline Winds (mph)
Friday Evening SW 5-15
Friday Night SSW 15-25
Saturday Morning SW 20-30
Saturday Afternoon SW 40-55
East South Ridgeline Winds (mph)
Friday Evening SSW 5-15
Friday Night SW 10-20
Saturday Morning WSW 25-35
Saturday Afternoon WSW 40-55
Mt. Hood Ridgeline Winds (mph)
Friday Evening SW 10-20
Friday Night WSW 20-30
Saturday Morning WSW 25-35
Saturday Afternoon WSW 40-55

Issued: 2:13 PM PST Friday, December 17, 2021

Extended Weather Synopsis

We'll be in split-flow Sunday night through the extended with a cut-off low off th California coast and NW flow carving out a trough over western Canada, leaving the PNW in a bit of no man's land. Eventually, moisture will rotate up from the south but the timing and intensity are tough to pin down in this pattern. We can say with higher confidence that gradients and winds will remain offshore (east or southeasterly) with cooler temps on the east side of the Cascades and some milder air along the west slopes of the Cascades and Olympics.  

Extended Snow Level (ft)

Sunday Night* Monday * Monday Night* Tuesday *
West North 0 1500' 2000' 3500'
Snoqualmie Pass 1000' 2000' 3000' 3000'
Mt. Hood 2000' 4000' 3000' 3000'
West North Elevation
Sunday Night* 0'
Monday * 1500'
Monday Night* 2000'
Tuesday * 3500'
Snoqualmie Pass Elevation
Sunday Night* 1000'
Monday * 2000'
Monday Night* 3000'
Tuesday * 3000'
Mt. Hood Elevation
Sunday Night* 2000'
Monday * 4000'
Monday Night* 3000'
Tuesday * 3000'

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

Previous forecast from Dec 17, 2021

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’.