Issued: 3:04 PM PST Monday, December 20, 2021
by Robert Hahn

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

Weather Synopsis

Forecast updated 3 PM to fix a typo in the West South Snow level.

The warm front bringing moderate to heavy rain and snow to southern Washington and Northern Oregon on Monday fizzles as the energy gets taken up by a large-scale closed low off the Northern California coastline. The lower atmosphere has become relatively isothermal west of the Cascade Crest by Monday afternoon as warm air moves in aloft. Warm air continues to spill into the region and will increasingly erode the cold air in the northern Washington Cascades and east of the Cascade Crest. Rain and snow over the southern and central Washington Cascades should taper quickly into the light range and will end in many areas by midnight. Some areas may see a period of light freezing rain overnight as warmer air overruns shallow cold air remaining east of the Cascade Crest that continues to filter through the mountain gaps on easterly flow.

A very weak and poorly-defined frontal feature may bring some very light rain and high elevation snow to parts of the northern and central Cascades on Tuesday. Snow levels will be in the 4000-5000 ft range. Ridgeline winds will increase into the moderate range for parts of the east slopes of the Cascades as flow turns westerly.

Rain and snow ramp up ahead of a tight, but strong low dropping down the west coast of Canada on Tuesday night. We expect 0.5-1" of snow water equivalent (SWE) to fall along the west slopes of the Cascades with 0.5" of SWE or less along the east slopes. Snow levels remain elevated in the 4000-5500 ft range and WSW winds will increase.

Wednesday looks similar to Tuesday night, but snow levels should drop to the 3000-4000 ft range as the approaching low brings cooling to the region. SW winds should favor the Cascades volcanoes.

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
Monday Night Mostly cloudy. Milder.
Tuesday Partly cloudy in the morning, then mostly cloudy in the afternoon. Mild.
Monday Night Mostly cloudy.
Tuesday Cloudy with a chance of rain or snow late showers. Rising snow levels.
Monday Night Light rain or snow possible in the evening, then becoming mostly cloudy. Milder.
Tuesday Mostly cloudy with very light rain or high elevation snow possible late in the day.
Monday Night Rain and snow rapidly decreasing or ending during the evening hours then becoming cloudy and milder.
Tuesday Cloudy with a chance of light rain or high elevation snow later in the day.
Monday Night Milder with periods of light snow or snow showers. A chance of light freezing rain mainly after midnight. Light E winds at the Pass.
Tuesday Cloudy with very light rain or high elevation snow showers, mainly in the afternoon
Monday Night Milder with periods of light snow in the evening possibly changing to freezing rain during the early morning hours. Light E winds at the Pass.
Tuesday Cloudy with very light light rain or high elevation snow most likely during the afternoon.
Monday Night Cloudy with a slight chance of very light precipitation including freezing rain overnight. Milder.
Tuesday Mostly cloudy. Milder.
Monday Night Light snow at times, possibly mixing with rain or freezing rain late. Milder.
Tuesday Mostly cloudy. Milder.
Monday Night Light rain or snow, ending during the evening hours. Milder.
Tuesday Mostly cloudy.
Monday Night Light rain and snow in the evening, then becoming cloudy with a chance of freezing rain at lower elevations overnight.
Tuesday Partly to mostly cloudy. Mild.

Issued: 3:04 PM PST Monday, December 20, 2021

Precipitation (in)

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

Issued: 3:04 PM PST Monday, December 20, 2021

Snow Level (ft)

Monday Evening* Monday Night* Tuesday Morning* Tuesday Afternoon* Tuesday Evening* Tuesday Night* Wednesday Morning Wednesday Afternoon
Olympics 3500' 5000' 5500' 6000' 5000' 4500' 3500' 3500'
West North 1000' 1000' 2500' 4000' 4000' 3500' 3000' 3000'
West Central 2500' 4000' 5500' 4500' 4500' 4000' 3500' 3500'
West South 4000' 4500' 6000' 6500' 5500' 4500' 3500' 3500'
Stevens Pass 2000' 3000' 4500' 5000' 5000' 4000' 3500' 3500'
Snoqualmie Pass 2000' 4000' 4500' 5000' 5000' 4500' 3500' 3500'
East North 1000' 1000' 2500' 4500' 3500' 3500' 3000' 3500'
East Central 1500' 2000' 3000' 4500' 4500' 4000' 3500' 3500'
East South 4000' 4500' 6000' 6500' 6000' 5000' 4000' 3500'
Mt. Hood 5500' 6000' 4500' 7000' 5500' 4500' 4000' 3500'
Olympics Elevation
Monday Evening* 3500'
Monday Night* 5000'
Tuesday Morning* 5500'
Tuesday Afternoon* 6000'
Tuesday Evening* 5000'
Tuesday Night* 4500'
Wednesday Morning 3500'
Wednesday Afternoon 3500'
West North Elevation
Monday Evening* 1000'
Monday Night* 1000'
Tuesday Morning* 2500'
Tuesday Afternoon* 4000'
Tuesday Evening* 4000'
Tuesday Night* 3500'
Wednesday Morning 3000'
Wednesday Afternoon 3000'
West Central Elevation
Monday Evening* 2500'
Monday Night* 4000'
Tuesday Morning* 5500'
Tuesday Afternoon* 4500'
Tuesday Evening* 4500'
Tuesday Night* 4000'
Wednesday Morning 3500'
Wednesday Afternoon 3500'
West South Elevation
Monday Evening* 4000'
Monday Night* 4500'
Tuesday Morning* 6000'
Tuesday Afternoon* 6500'
Tuesday Evening* 5500'
Tuesday Night* 4500'
Wednesday Morning 3500'
Wednesday Afternoon 3500'
Stevens Pass Elevation
Monday Evening* 2000'
Monday Night* 3000'
Tuesday Morning* 4500'
Tuesday Afternoon* 5000'
Tuesday Evening* 5000'
Tuesday Night* 4000'
Wednesday Morning 3500'
Wednesday Afternoon 3500'
Snoqualmie Pass Elevation
Monday Evening* 2000'
Monday Night* 4000'
Tuesday Morning* 4500'
Tuesday Afternoon* 5000'
Tuesday Evening* 5000'
Tuesday Night* 4500'
Wednesday Morning 3500'
Wednesday Afternoon 3500'
East North Elevation
Monday Evening* 1000'
Monday Night* 1000'
Tuesday Morning* 2500'
Tuesday Afternoon* 4500'
Tuesday Evening* 3500'
Tuesday Night* 3500'
Wednesday Morning 3000'
Wednesday Afternoon 3500'
East Central Elevation
Monday Evening* 1500'
Monday Night* 2000'
Tuesday Morning* 3000'
Tuesday Afternoon* 4500'
Tuesday Evening* 4500'
Tuesday Night* 4000'
Wednesday Morning 3500'
Wednesday Afternoon 3500'
East South Elevation
Monday Evening* 4000'
Monday Night* 4500'
Tuesday Morning* 6000'
Tuesday Afternoon* 6500'
Tuesday Evening* 6000'
Tuesday Night* 5000'
Wednesday Morning 4000'
Wednesday Afternoon 3500'
Mt. Hood Elevation
Monday Evening* 5500'
Monday Night* 6000'
Tuesday Morning* 4500'
Tuesday Afternoon* 7000'
Tuesday Evening* 5500'
Tuesday Night* 4500'
Wednesday Morning 4000'
Wednesday Afternoon 3500'

Issued: 3:04 PM PST Monday, December 20, 2021

5000' Temperatures (°F)

Monday Night Tuesday
Max / Min Max / Min
Olympics 33 / 26 35 / 31
West North 23 / 20 32 / 26
West Central 31 / 24 33 / 31
West South 33 / 29 36 / 30
Stevens Pass 32 / 27 34 / 32
Snoqualmie Pass 32 / 29 34 / 31
East North 24 / 17 32 / 24
East Central 31 / 27 34 / 30
East South 33 / 30 35 / 28
Mt. Hood 33 / 27 38 / 27
Olympics 5000' Temperature Forecast
(Max / Min)
Monday Night 33 / 26
Tuesday 35 / 31
West North 5000' Temperature Forecast
(Max / Min)
Monday Night 23 / 20
Tuesday 32 / 26
West Central 5000' Temperature Forecast
(Max / Min)
Monday Night 31 / 24
Tuesday 33 / 31
West South 5000' Temperature Forecast
(Max / Min)
Monday Night 33 / 29
Tuesday 36 / 30
Stevens Pass 5000' Temperature Forecast
(Max / Min)
Monday Night 32 / 27
Tuesday 34 / 32
Snoqualmie Pass 5000' Temperature Forecast
(Max / Min)
Monday Night 32 / 29
Tuesday 34 / 31
East North 5000' Temperature Forecast
(Max / Min)
Monday Night 24 / 17
Tuesday 32 / 24
East Central 5000' Temperature Forecast
(Max / Min)
Monday Night 31 / 27
Tuesday 34 / 30
East South 5000' Temperature Forecast
(Max / Min)
Monday Night 33 / 30
Tuesday 35 / 28
Mt. Hood 5000' Temperature Forecast
(Max / Min)
Monday Night 33 / 27
Tuesday 38 / 27

Issued: 3:04 PM PST Monday, December 20, 2021

Ridgeline Winds (mph)

Monday Evening Monday Night Tuesday Morning Tuesday Afternoon
Olympics SW 5-15 SW 5-15 WSW 10-20 SW 10-20
West North SSW 0-10 SW 5-15 WSW 10-20 WSW 10-20
West Central SW 0-10 WSW 5-15 WSW 5-15 WSW 10-20
West South WSW 0-10 SW 0-10 WSW 0-10 WSW 0-10
Stevens Pass W 0-10 WSW 0-10 W 5-15 WSW 10-20
Snoqualmie Pass W 5-15 W 5-15 W 5-15 W 5-15
East North W 5-15 WSW 10-20 WSW 15-25 W 15-25
East Central W 10-20 W 10-20 W 15-25 W 15-25
East South W 5-15 WSW 0-10 WSW 0-10 WSW 0-10
Mt. Hood WSW 5-15 SW 5-15 WSW 5-15 WSW 5-15
Olympics Ridgeline Winds (mph)
Monday Evening SW 5-15
Monday Night SW 5-15
Tuesday Morning WSW 10-20
Tuesday Afternoon SW 10-20
West North Ridgeline Winds (mph)
Monday Evening SSW 0-10
Monday Night SW 5-15
Tuesday Morning WSW 10-20
Tuesday Afternoon WSW 10-20
West Central Ridgeline Winds (mph)
Monday Evening SW 0-10
Monday Night WSW 5-15
Tuesday Morning WSW 5-15
Tuesday Afternoon WSW 10-20
West South Ridgeline Winds (mph)
Monday Evening WSW 0-10
Monday Night SW 0-10
Tuesday Morning WSW 0-10
Tuesday Afternoon WSW 0-10
Stevens Pass Ridgeline Winds (mph)
Monday Evening W 0-10
Monday Night WSW 0-10
Tuesday Morning W 5-15
Tuesday Afternoon WSW 10-20
Snoqualmie Pass Ridgeline Winds (mph)
Monday Evening W 5-15
Monday Night W 5-15
Tuesday Morning W 5-15
Tuesday Afternoon W 5-15
East North Ridgeline Winds (mph)
Monday Evening W 5-15
Monday Night WSW 10-20
Tuesday Morning WSW 15-25
Tuesday Afternoon W 15-25
East Central Ridgeline Winds (mph)
Monday Evening W 10-20
Monday Night W 10-20
Tuesday Morning W 15-25
Tuesday Afternoon W 15-25
East South Ridgeline Winds (mph)
Monday Evening W 5-15
Monday Night WSW 0-10
Tuesday Morning WSW 0-10
Tuesday Afternoon WSW 0-10
Mt. Hood Ridgeline Winds (mph)
Monday Evening WSW 5-15
Monday Night SW 5-15
Tuesday Morning WSW 5-15
Tuesday Afternoon WSW 5-15

Issued: 3:04 PM PST Monday, December 20, 2021

Extended Weather Synopsis

The open low sliding down the west coast of Canada becomes a cold trough as it approaches the Pacific Northwest Wednesday night. Moderate to strong SW winds should bring plentiful moisture into the Cascades which should pick up 0.5-1.5" of snow water equivalent. Models bringing the trough across the Cascades Thursday morning, resulting in more showery precipitation and convergence activity with approximately another 0.5" of snow water equivalent for locations near and west of the Cascade Crest.

Another open trough sliding down the Canadian Coast arrives late Thursday night into Friday morning with more sustained snowfall.

Snow levels start off in the 3000-3500 ft range, but drop quickly Wednesday night, trending lower throughout the latter half of the week They should end the week in the 500-1500 ft range.

 

Extended Snow Level (ft)

Wednesday Night* Thursday Thursday Night Friday
West North 2500' 1000' 500' 500'
Snoqualmie Pass 2500' 1500' 1000' 500'
Mt. Hood 3500' 2000' 1500' 1500'
West North Elevation
Wednesday Night* 2500'
Thursday 1000'
Thursday Night 500'
Friday 500'
Snoqualmie Pass Elevation
Wednesday Night* 2500'
Thursday 1500'
Thursday Night 1000'
Friday 500'
Mt. Hood Elevation
Wednesday Night* 3500'
Thursday 2000'
Thursday Night 1500'
Friday 1500'

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

Previous forecast from Dec 20, 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’.