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Mountain Weather Forecast

Issued: 3:08 PM PST Wednesday, January 3, 2018
by Robert Hahn

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.

Weather synopsis for Wednesday & Thursday

On Wednesday, the ridge has rebuilt over the Pacific Northwest keeping snow/freezing levels mild and offshore easterly flow in the light to moderate range through the short term. A weak shortwave trough which progressed to our east Tuesday night mixed the atmosphere slightly. This mixing has resulted in decreased low level cloud coverage. Isolated clouds along with cooler temperatures will be seen in the Cascade Passes, lower elevations along the east slopes of the Cascades and Mt. Hood.  A weak upper shortwave trough embedded in a open trough rotating off the California coast will begin to move northward on Wednesday.

On Wednesday night, the ridge shifts east of the Cascades as the weak upper shortwave trough continues to move northward off the Oregon Coast.

On Thursday, occasional light precipitation spreads into region as the weak shortwave trough loses its identity as it begins moves northward into the Pacific Northwest on SW flow ahead of a trough to the west.

On Thursday night, the remnants of the weak shortwave trough continue to bring generally light amounts of moisture and a slight increase in winds to the Washington Cascades.

Weather forecast for Wednesday & Thursday

Olympics
Date Weather
Wednesday Mostly sunny and mild.
Wednesday Night Mostly clear and mild with increasing clouds high clouds after midnight.
Thursday Clouds lowering in the morning with occasional light rain in the afternoon.
Increasing light rain.
Washington Cascades near and west of the Crest including Stevens, Snoqualmie and White Passes
Date Weather
Wednesday Mostly sunny and mild. Cooler temperatures and isolated low clouds in the Cascade Passes.
Wednesday Night Mild with increasing high clouds in the south Cascades.
Thursday Clouds increase and lower with occasional light rain arriving in the south and then central Cascades by afternoon. Precipitation should be freezing rain or snow in the passes.
Light rain with freezing rain or snow in the passes continues and spreads northward, becoming light to moderate by morning.
East Slopes of the Washington Cascades
Date Weather
Wednesday Mostly sunny and mild at higher elevations. Colder at low elevations with isolated low clouds in valleys.
Wednesday Night Mild at higher elevations with increasing clouds in the south. Colder at low elevations with isolated low clouds in valleys.
Thursday Clouds increase and occasional light rain, freezing rain or snow arrives in the south and then central Cascades by afternoon.
Light rain, freezing rain or snow spreads northward and becomes light to moderate by morning.
Mt. Hood
Date Weather
Wednesday Mostly sunny and mild with decreasing high clouds . Cooler temperatures and isolated low clouds in the Cascade Passes.
Wednesday Night Mild with increasing high clouds, lowering towards morning.
Thursday Clouds increase and light rain and high elevation snow arrives in the late morning hours.
Periods of light rain and high elevation snow.

Snow Level/Freezing Level in feet

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Wednesday Afternoon Freezing Level 9500' 9000' 7500' 8500' 10000' *
Wednesday Night Freezing Level 9500' 9500' 7000' 9500' 10000' *
Thursday Morning Snow Level 7500' 7500' 5500' 6000' 7500' *
Thursday Afternoon Snow Level 7000' 6500' 4500' 6000' 7000' *
Olympics
Date Elevation
Wednesday Afternoon Freezing Level
9500'
Easterly Flow*
Wednesday Night Freezing Level
9500'
Easterly Flow*
Thursday Morning Snow Level
7500'
Easterly Flow*
Thursday Afternoon Snow Level
7000'
Easterly Flow*
Thursday Night Snow Level
7000'
Easterly Flow*
Northwest Cascades
Date Elevation
Wednesday Afternoon Freezing Level
9000'
Easterly Flow*
Wednesday Night Freezing Level
9500'
Easterly Flow*
Thursday Morning Snow Level
7500'
Easterly Flow*
Thursday Afternoon Snow Level
6500'
Easterly Flow*
Thursday Night Snow Level
7000'
Easterly Flow*
Northeast Cascades
Date Elevation
Wednesday Afternoon Freezing Level
7500'
Easterly Flow*
Wednesday Night Freezing Level
7000'
Easterly Flow*
Thursday Morning Snow Level
5500'
Easterly Flow*
Thursday Afternoon Snow Level
4500'
Easterly Flow*
Thursday Night Snow Level
5000'
Easterly Flow*
Central Cascades
Date Elevation
Wednesday Afternoon Freezing Level
8500'
Easterly Flow*
Wednesday Night Freezing Level
9500'
Easterly Flow*
Thursday Morning Snow Level
6000'
Easterly Flow*
Thursday Afternoon Snow Level
6000'
Easterly Flow*
Thursday Night Snow Level
6500'
Easterly Flow*
South Cascades
Date Elevation
Wednesday Afternoon Freezing Level
10000'
Easterly Flow*
Wednesday Night Freezing Level
10000'
Easterly Flow*
Thursday Morning Snow Level
7500'
Easterly Flow*
Thursday Afternoon Snow Level
7000'
Easterly Flow*
Thursday Night Snow Level
7000'
Easterly Flow*

Cascade Snow / Freezing Levels noted above refer to the north (approximately Mt Baker and Washington Pass), central (approximately Stevens to White Pass) and south (near Mt Hood). Freezing Level is when no precipitation is forecast.
* Note that surface snow levels are common near the passes during easterly pass flow and may result in multiple snow / freezing levels.

24 Hour Quantitative Precipitation ending at 4 am

Location Thu Fri
Hurricane Ridge 0 lt .10
Mt Baker Ski Area 0 lt .25
Washington Pass 0 lt .10
Stevens Pass 0 lt .10
Snoqualmie Pass 0 lt .25
Mission Ridge 0 lt .10
Crystal Mt 0 lt .25
Paradise 0 .50 - .75
White Pass 0 lt .25
Mt Hood Meadows 0 lt .25

Winds in Miles per Hour (MPH) "Cascade Pass Level Winds"

Date Direction - Speed
Wednesday Afternoon E 20 - 30
Wednesday Night E 20 - 30
Thursday Morning E 15 - 25
Thursday Afternoon E 15 - 25

Directions above indicate the direction the wind blows from on the 16-point cardinal scale. Winds near the passes tend to be highly channeled by the topography and normally blow either easterly or westerly depending on the surface pressure gradients that drive such winds.

Free Winds at 5000' (in Miles per Hour (MPH))

Date Olympics Northwest Cascades Central Cascades South Cascades
Wednesday Afternoon ESE 5 - 15 E 5 - 15 E 10 - 20 E 10 - 20
Wednesday Night SSE 5 - 15 ESE 5 - 15 E 10 - 20 E 10 - 20
Thursday Morning SSE 5 - 15 ESE 5 - 15 ESE 10 - 20 SE 5 - 15
Thursday Afternoon S 5 - 15 SE 5 - 15 SE 5 - 15 SSE 5 - 15
Olympics
Date Elevation
Wednesday Afternoon ESE 5 - 15
Wednesday Night SSE 5 - 15
Thursday Morning SSE 5 - 15
Thursday Afternoon S 5 - 15
Thursday Night SSE 10 - 20
Northwest Cascades
Date Elevation
Wednesday Afternoon E 5 - 15
Wednesday Night ESE 5 - 15
Thursday Morning ESE 5 - 15
Thursday Afternoon SE 5 - 15
Thursday Night SE 10 - 20
Central Cascades
Date Elevation
Wednesday Afternoon E 10 - 20
Wednesday Night E 10 - 20
Thursday Morning ESE 10 - 20
Thursday Afternoon SE 5 - 15
Thursday Night ESE 10 - 20
South Cascades
Date Elevation
Wednesday Afternoon E 10 - 20
Wednesday Night E 10 - 20
Thursday Morning SE 5 - 15
Thursday Afternoon SSE 5 - 15
Thursday Night ESE 10 - 20
Olympics
Date Direction - Speed
Wednesday Afternoon ESE 5 - 15
Wednesday Night SSE 5 - 15
Thursday Morning SSE 5 - 15
Thursday Afternoon S 5 - 15
Thursday Night SSE 10 - 20
Northwest Cascades
Date Direction - Speed
Wednesday Afternoon E 5 - 15
Wednesday Night ESE 5 - 15
Thursday Morning ESE 5 - 15
Thursday Afternoon SE 5 - 15
Thursday Night SE 10 - 20
Central Cascades
Date Direction - Speed
Wednesday Afternoon E 10 - 20
Wednesday Night E 10 - 20
Thursday Morning ESE 10 - 20
Thursday Afternoon SE 5 - 15
Thursday Night ESE 10 - 20
South Cascades
Date Direction - Speed
Wednesday Afternoon E 10 - 20
Wednesday Night E 10 - 20
Thursday Morning SE 5 - 15
Thursday Afternoon SSE 5 - 15
Thursday Night ESE 10 - 20

Directions above indicate the direction the wind blows from on the 16-point cardinal scale. These winds and the 9000 ft winds below also indicate "free" winds, or those winds in the atmosphere not influenced by terrain. Topographical effects may produce greater or lower wind speeds in certain locations as well as significant variations in direction.

Free Winds at 9000' (in Miles per Hour (MPH))

Date Northwest Cascades Northeast Cascades Central Cascades South Cascades
Wednesday Afternoon SW 5 - 15 SW 5 - 15 WSW 10 - 20 SW 10 - 20
Wednesday Night SSW 10 - 20 SW 10 - 20 S 5 - 15 S 10 - 20
Thursday Morning S 10 - 20 SW 10 - 20 SSE 10 - 20 SW 25 - 35
Thursday Afternoon SSW 10 - 20 S 5 - 15 SW 20 - 30 WSW 20 - 30
Northwest Cascades
Date Direction - Speed
Wednesday Afternoon SW 5 - 15
Wednesday Night SSW 10 - 20
Thursday Morning S 10 - 20
Thursday Afternoon SSW 10 - 20
Thursday Night SSW 20 - 30
Northeast Cascades
Date Direction - Speed
Wednesday Afternoon SW 5 - 15
Wednesday Night SW 10 - 20
Thursday Morning SW 10 - 20
Thursday Afternoon S 5 - 15
Thursday Night SSW 15 - 25
Central Cascades
Date Direction - Speed
Wednesday Afternoon WSW 10 - 20
Wednesday Night S 5 - 15
Thursday Morning SSE 10 - 20
Thursday Afternoon SW 20 - 30
Thursday Night SSW 25 - 35
South Cascades
Date Direction - Speed
Wednesday Afternoon SW 10 - 20
Wednesday Night S 10 - 20
Thursday Morning SW 25 - 35
Thursday Afternoon WSW 20 - 30
Thursday Night SSW 15 - 25

Extended Weather Synopsis for Friday through Sunday

On Friday, the larger low over the North Pacific rotates another shortwave trough, ejecting a closed upper level and surface low NNW toward the Pacific Northwest, arriving in the Washington coastal waters by Friday evening. The mildly organized and slightly weakening surface low and associated front should move over the region Friday late evening bringing a renewed round of precipitation.

The closed low rejoins the parent trough over British Columbia, bringing cooler NW flow late Friday night and Saturday morning with post-frontal showers decreasing and a drying trend as a shortwave ridge moves over the region Saturday.

Sunday will feature moist onshore flow ahead of an elongated frontal band and rotating surface and upper level low pressures off the coast of Vancouver Island. The precipitation should start cool and arrive on a warming trend.

Extended Weather Forecast for Friday through Sunday

Olympics, Washington Cascades and Mt. Hood Area
Date Weather
Friday Precipitation lifts northward, bringing mostly very light rain and snow showers to most areas, but light to moderate rain and snow showers in the NW Cascades, particularly Baker area. Friday night brings light to moderate rain and snow to the Olympics and west slopes with light rain and snow elsewhere. Precipitation becomes showery after midnight with cooling.
Saturday Decreasing light rain and snow showers in the morning, heaviest west slopes Cascades and Hood. Cooler. Becoming partly cloudy in the afternoon.

Snow/Freezing Levels

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Friday Snow Level 4500' - 5500' 4000' - 5000' 4000' - 5000' 4500' - 5500' 6000' - 7000' *
Friday Night Snow Level 3500' - 5500' 4500' - 5500' 3000' - 4000' 4000' - 6000' 5000' - 7000'
Saturday Snow Level 2000' - 4000' 2000' - 4000' 2000' - 4000' 2000' - 4000' 3000' - 5000'
Saturday Night Snow Level 2500' - 4500' 1000' - 3000' 500' - 2500' 1500' - 3500' 3500' - 5500'
Olympics
Date Elevation
Friday Snow Level
4500' - 5500'
Easterly Flow*
Friday Night Snow Level
3500' - 5500'
Saturday Snow Level
2000' - 4000'
Saturday Night Snow Level
2500' - 4500'
Sunday Snow Level
4000' - 6000'
Northwest Cascades
Date Elevation
Friday Snow Level
4000' - 5000'
Easterly Flow*
Friday Night Snow Level
4500' - 5500'
Saturday Snow Level
2000' - 4000'
Saturday Night Snow Level
1000' - 3000'
Sunday Snow Level
2500' - 4500'
Northeast Cascades
Date Elevation
Friday Snow Level
4000' - 5000'
Easterly Flow*
Friday Night Snow Level
3000' - 4000'
Saturday Snow Level
2000' - 4000'
Saturday Night Snow Level
500' - 2500'
Sunday Snow Level
2500' - 4500'
Central Cascades
Date Elevation
Friday Snow Level
4500' - 5500'
Easterly Flow*
Friday Night Snow Level
4000' - 6000'
Saturday Snow Level
2000' - 4000'
Saturday Night Snow Level
1500' - 3500'
Sunday Snow Level
3500' - 5500'
South Cascades
Date Elevation
Friday Snow Level
6000' - 7000'
Easterly Flow*
Friday Night Snow Level
5000' - 7000'
Saturday Snow Level
3000' - 5000'
Saturday Night Snow Level
3500' - 5500'
Sunday Snow Level
5000' - 7000'

Freezing Level is when no precipitation is forecast.
* Note that surface snow levels are common near the passes during easterly pass flow and may result in multiple snow / freezing levels.