Issued: 3:40 PM PST Saturday, December 19, 2020
by Robert Hahn

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

Weather Synopsis

A warm and very wet system tapping into a subtropical moisture feed will unload on the Pacific Northwest Saturday night. A warm front lifted across northern Washington Saturday evening with heavy rain and snow associated with an extended cold-frontal rainband moving into the region from the west. Expect very heavy rain and snow with snow levels spiking in all areas during the evening hours and peaking in the 5000-8000 ft range overnight. The cold front works through the region overnight from NW to SE and lingers longer over the southern Washington Cascades and Mt. Hood regions. We expect 1-3"+ of water equivalent overnight.

Sunday will bring cooler weather to Washington state, with decreasing light rain and snow showers. Rain and snow will focus on Mt. Hood and Oregon where the frontal band stalls, maintaining very mild conditions and strong winds.

A wave develops a surface low on Sunday with a track aiming it directly at Washington State from the WSW in the latest model runs. With a strong warm front lifting northward over the region and E flow ahead of the front Sunday night, expect significant upslope flow and accumulation of rain and snow on the E side of the Cascades and Olympics. The cold front behind that follows is quite strong with a significant temperature gradient and wind direction shift. A more southerly track will result in a significant snow event for parts of the Cascades and Olympics, while a more northerly track will keep our region in the warm sector significantly longer. Either way, the cold front should pass the Cascades during the mid-day hours on Monday, allowing snow levels to drop and a period of intense post-frontal NW flow Monday afternoon.

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 Moderate to heavy rain and high elevation snow becoming light showers after midnight. Mild. Strong wind gusts.
Sunday Cloudy.
Saturday Night Heavy rain and snow in the early evening, decreasing to light by morning. Warming until shortly after midnight, then cooling. Strong winds in the evening.
Sunday Light to occasionally moderate rain and snow showers.
Saturday Night Heavy rain and high elevation snow in the evening, becoming light to moderate showers after midnight. Warming trend. Strong winds in the evening. Strong winds in the evening.
Sunday Light rain and snow showers. Cooler.
Saturday Night Very heavy (Paradise and White Pass) and moderate to heavy (Crystal) rain and snow. Strong winds in the evening.
Sunday Northern part: Light rain and snow in the morning, then becoming cloudy. Southern part: Moderate rain and snow becoming light.
Saturday Night Heavy rain and high elevation snow. Rapid warming trend in the evening. Strong ridgeline winds in the evening. Light to moderate E winds at pass level switching W in the evening. Light to moderate E winds at pass level switching to moderate W in the evening.
Sunday Light rain/snow showers and convergence activity decreasing during the morning hours and possibly ending. Pass-level winds light to moderate westerly.
Saturday Night Heavy rain and high elevation snow. Rapid warming trend in the evening. Ridgeline winds ramping up to strong overnight. Light to moderate E winds at pass level switching to moderate W in the evening.
Sunday Light rain/snow showers and convergence activity decreasing during the morning hours and possibly ending. Pass-level winds light to moderate westerly.
Saturday Night Heavy rain and high elevation snow in the evening, becoming moderate. Warming trend from 7 PM to midnight. Strong winds overnight.
Sunday Decreasing light snow showers. Strong winds in the morning.
Saturday Night Heavy rain and high elevation snow in the evening, becoming moderate. Warming trend from 7 PM to midnight. Strong winds.
Sunday Decreasing light rain and snow showers. Strong winds in the morning.
Saturday Night Heavy rain and high elevation snow in the evening, becoming moderate. Warming trend from 7 PM to midnight. Strong winds.
Sunday Decreasing light rain and snow showers. Strong winds in the morning.
Saturday Night Increasing very heavy rain and high elevation snow. Rapid warming during the evening hours, becoming very mild. Very strong to extreme ridgeline winds.
Sunday Heavy rain and high elevation snow decreasing to moderate in the afternoon. Very mild. Strong winds.

Issued: 3:40 PM PST Saturday, December 19, 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 0.75 0 0.50 1.00
Mt Baker Ski Area 1.00 - 1.50 LT 0.25 0.25 1.50
Mt. Loop - Barlow Pass 1.50 - 2.00 LT 0.25 0.25 - 0.50 1.00 - 1.50
Stevens Pass 1.50 0.25 0.50 0.50 - 0.75
Snoqualmie Pass 1.50 - 2.00 LT 0.25 0.75 0.75
Crystal Mt 0.75 LT 0.10 0.25 - 0.50 0.50 - 0.75
Paradise 2.50 - 3.50 0.25 1.00 1.00
White Pass 1.50 - 2.00 0.25 0.50 - 0.75 0.50
Washington Pass 1.00 LT 0.10 0.25 - 0.50 1.00
Mission Ridge 0.75 -1.00 LT 0.10 0.25 - 0.50 0.25
Salmon la Sac - Gallagher Head 1.50 LT 0.10 0.50 0.50 - 0.75
Tieton River - Darland Mt. 1.00 - 1.50 LT 0.25 0.50 0.25 - 0.50
Mt Hood Meadows 2.50 - 3.50 1.50 1.00 0.50
Timberline 2.50 - 3.50 1.50 1.00 - 1.50 0.50
Hurricane Ridge Precipitation (in)
Saturday Night 0.75
Sunday 0
Sunday Night 0.50
Monday 1.00
Mt Baker Ski Area Precipitation (in)
Saturday Night 1.00 - 1.50
Sunday LT 0.25
Sunday Night 0.25
Monday 1.50
Mt. Loop - Barlow Pass Precipitation (in)
Saturday Night 1.50 - 2.00
Sunday LT 0.25
Sunday Night 0.25 - 0.50
Monday 1.00 - 1.50
Stevens Pass Precipitation (in)
Saturday Night 1.50
Sunday 0.25
Sunday Night 0.50
Monday 0.50 - 0.75
Snoqualmie Pass Precipitation (in)
Saturday Night 1.50 - 2.00
Sunday LT 0.25
Sunday Night 0.75
Monday 0.75
Crystal Mt Precipitation (in)
Saturday Night 0.75
Sunday LT 0.10
Sunday Night 0.25 - 0.50
Monday 0.50 - 0.75
Paradise Precipitation (in)
Saturday Night 2.50 - 3.50
Sunday 0.25
Sunday Night 1.00
Monday 1.00
White Pass Precipitation (in)
Saturday Night 1.50 - 2.00
Sunday 0.25
Sunday Night 0.50 - 0.75
Monday 0.50
Washington Pass Precipitation (in)
Saturday Night 1.00
Sunday LT 0.10
Sunday Night 0.25 - 0.50
Monday 1.00
Mission Ridge Precipitation (in)
Saturday Night 0.75 -1.00
Sunday LT 0.10
Sunday Night 0.25 - 0.50
Monday 0.25
Salmon la Sac - Gallagher Head Precipitation (in)
Saturday Night 1.50
Sunday LT 0.10
Sunday Night 0.50
Monday 0.50 - 0.75
Tieton River - Darland Mt. Precipitation (in)
Saturday Night 1.00 - 1.50
Sunday LT 0.25
Sunday Night 0.50
Monday 0.25 - 0.50
Mt Hood Meadows Precipitation (in)
Saturday Night 2.50 - 3.50
Sunday 1.50
Sunday Night 1.00
Monday 0.50
Timberline Precipitation (in)
Saturday Night 2.50 - 3.50
Sunday 1.50
Sunday Night 1.00 - 1.50
Monday 0.50

Issued: 3:40 PM PST Saturday, December 19, 2020

Snow Level (ft)

Saturday Evening* Saturday Night Sunday Morning Sunday Afternoon Sunday Evening Sunday Night* Monday Morning* Monday Afternoon
Olympics 6000' 5500' 4500' 4000' 3500' 3500' 4000' 3000'
West North 3500' 5000' 4000' 3500' 3000' 2500' 3000' 3000'
West Central 4500' 5500' 4500' 3500' 3500' 3500' 5000' 4500'
West South 4500' 6500' 5500' 4500' 4000' 5500' 6000' 5500'
Stevens Pass 4000' 5500' 4500' 4000' 7500' 3500' 5000' 4500'
Snoqualmie Pass 4500' 6000' 5000' 4000' 3500' 4500' 5500' 5000'
East North 3500' 4500' 4500' 4000' 3000' 2500' 3000' 3500'
East Central 4000' 6000' 5000' 4000' 3500' 4000' 5000' 5000'
East South 5000' 7000' 5500' 5000' 4500' 6500' 6500' 6000'
Mt. Hood 6000' 8000' 7000' 7000' 7500' 8000' 7000' 6500'
Olympics Elevation
Saturday Evening* 6000'
Saturday Night 5500'
Sunday Morning 4500'
Sunday Afternoon 4000'
Sunday Evening 3500'
Sunday Night* 3500'
Monday Morning* 4000'
Monday Afternoon 3000'
West North Elevation
Saturday Evening* 3500'
Saturday Night 5000'
Sunday Morning 4000'
Sunday Afternoon 3500'
Sunday Evening 3000'
Sunday Night* 2500'
Monday Morning* 3000'
Monday Afternoon 3000'
West Central Elevation
Saturday Evening* 4500'
Saturday Night 5500'
Sunday Morning 4500'
Sunday Afternoon 3500'
Sunday Evening 3500'
Sunday Night* 3500'
Monday Morning* 5000'
Monday Afternoon 4500'
West South Elevation
Saturday Evening* 4500'
Saturday Night 6500'
Sunday Morning 5500'
Sunday Afternoon 4500'
Sunday Evening 4000'
Sunday Night* 5500'
Monday Morning* 6000'
Monday Afternoon 5500'
Stevens Pass Elevation
Saturday Evening* 4000'
Saturday Night 5500'
Sunday Morning 4500'
Sunday Afternoon 4000'
Sunday Evening 7500'
Sunday Night* 3500'
Monday Morning* 5000'
Monday Afternoon 4500'
Snoqualmie Pass Elevation
Saturday Evening* 4500'
Saturday Night 6000'
Sunday Morning 5000'
Sunday Afternoon 4000'
Sunday Evening 3500'
Sunday Night* 4500'
Monday Morning* 5500'
Monday Afternoon 5000'
East North Elevation
Saturday Evening* 3500'
Saturday Night 4500'
Sunday Morning 4500'
Sunday Afternoon 4000'
Sunday Evening 3000'
Sunday Night* 2500'
Monday Morning* 3000'
Monday Afternoon 3500'
East Central Elevation
Saturday Evening* 4000'
Saturday Night 6000'
Sunday Morning 5000'
Sunday Afternoon 4000'
Sunday Evening 3500'
Sunday Night* 4000'
Monday Morning* 5000'
Monday Afternoon 5000'
East South Elevation
Saturday Evening* 5000'
Saturday Night 7000'
Sunday Morning 5500'
Sunday Afternoon 5000'
Sunday Evening 4500'
Sunday Night* 6500'
Monday Morning* 6500'
Monday Afternoon 6000'
Mt. Hood Elevation
Saturday Evening* 6000'
Saturday Night 8000'
Sunday Morning 7000'
Sunday Afternoon 7000'
Sunday Evening 7500'
Sunday Night* 8000'
Monday Morning* 7000'
Monday Afternoon 6500'

Issued: 3:40 PM PST Saturday, December 19, 2020

5000' Temperatures (°F)

Saturday Night Sunday
Max / Min Max / Min
Olympics 36 / 29 28 / 25
West North 34 / 28 29 / 27
West Central 35 / 29 30 / 28
West South 36 / 32 32 / 30
Stevens Pass 36 / 30 32 / 28
Snoqualmie Pass 36 / 30 32 / 29
East North 34 / 27 29 / 26
East Central 35 / 29 32 / 27
East South 36 / 31 32 / 28
Mt. Hood 38 / 33 38 / 35
Olympics 5000' Temperature Forecast
(Max / Min)
Saturday Night 36 / 29
Sunday 28 / 25
West North 5000' Temperature Forecast
(Max / Min)
Saturday Night 34 / 28
Sunday 29 / 27
West Central 5000' Temperature Forecast
(Max / Min)
Saturday Night 35 / 29
Sunday 30 / 28
West South 5000' Temperature Forecast
(Max / Min)
Saturday Night 36 / 32
Sunday 32 / 30
Stevens Pass 5000' Temperature Forecast
(Max / Min)
Saturday Night 36 / 30
Sunday 32 / 28
Snoqualmie Pass 5000' Temperature Forecast
(Max / Min)
Saturday Night 36 / 30
Sunday 32 / 29
East North 5000' Temperature Forecast
(Max / Min)
Saturday Night 34 / 27
Sunday 29 / 26
East Central 5000' Temperature Forecast
(Max / Min)
Saturday Night 35 / 29
Sunday 32 / 27
East South 5000' Temperature Forecast
(Max / Min)
Saturday Night 36 / 31
Sunday 32 / 28
Mt. Hood 5000' Temperature Forecast
(Max / Min)
Saturday Night 38 / 33
Sunday 38 / 35

Issued: 3:40 PM PST Saturday, December 19, 2020

Ridgeline Winds (mph)

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

Issued: 3:40 PM PST Saturday, December 19, 2020

Extended Weather Synopsis

Post-frontal W flow Monday evening along with a sharp, cold trough will allow significant snow accumulations for the Cascades. Overnight on Monday, the trough slides E and a significant ridge will begin moving into the region, resulting in drying northerly flow aloft and rapidly dwindling snow shower and convergence zone activity. Expect some low cloud to linger along the west slopes of the Cascades Tuesday, but partly skies will return to the region after a long hiatus. Expect a calm, clear Tuesday night. Wednesday should be mostly sunny with the ridge axis over our region and E flow developing as a system slated to arrive Friday begins to approach.

Extended Snow Level (ft)

Monday Night Tuesday Tuesday Night Wednesday *
West North 1500' 1000' 1500' 2500'
Snoqualmie Pass 2500' 1500' 1500' 3000'
Mt. Hood 3000' 2000' 3000' 4500'
West North Elevation
Monday Night 1500'
Tuesday 1000'
Tuesday Night 1500'
Wednesday * 2500'
Snoqualmie Pass Elevation
Monday Night 2500'
Tuesday 1500'
Tuesday Night 1500'
Wednesday * 3000'
Mt. Hood Elevation
Monday Night 3000'
Tuesday 2000'
Tuesday Night 3000'
Wednesday * 4500'

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

Previous forecast from Dec 19, 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’.