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Mountain Weather Forecast

Issued: 6:52 AM PST Thursday, December 8, 2016
by Garth Ferber

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 Thursday & Friday

Generally a cold clear day was seen on Wednesday. East winds have become strong at Snoqualmie and southeast winds at some sites along the crest have become strong such as Crystal by Thursday morning.

New models runs bring a little less moisture across the Olympics and Cascades and are a little slower to erode the Arctic air mass over the Northwest on Thursday.

A surface low pressure system will slowly approach over the northeast Pacific Ocean on Thursday. A warm front will swing south to north out of the low and over the Northwest - beginning the erosion of the Arctic air mass over the Northwest. This will cause some snow to gradually lift from south to north over the Olympics and Cascades on Thursday.

Strong east winds in the Cascades passes especially at Snoqualmie and strong southeast winds at some sites along the crest such as Crystal should continue much of Thursday.

A cold front will move out of the low and over the Northwest on Friday further eroding the Arctic air mass over the Northwest. This should further spread snow into the Olympics and Cascades on Friday. East winds should finally shift to west in the Cascades passes including Snoqualmie and winds at sites along the crest should shift to southwest by Friday night.

Weather forecast for Thursday & Friday

Olympics
Date Weather
Thursday Morning

Sunny.

Thursday Afternoon

Increasing clouds.

Thursday Night - Friday Morning

Light to moderate snow.

Friday Afternoon

Moderate snow.

Washington Cascades near and west of the crest including Stevens, Snoqualmie, and White Passes
Date Weather
Thursday Morning

Sunny north to central, increasing clouds south. Strong southeast winds at some sites along the crest. Strong east winds in the passes especially Snoqualmie.

Thursday Afternoon

Increasing clouds north to central, light snow south. Strong southeast winds at some sites along the crest. Strong east winds in the passes especially Snoqualmie.

Thursday Night - Friday Morning

Light to moderate snow.

Friday Afternoon

Moderate to heavy snow.

East slopes of the Washington Cascades
Date Weather
Thursday Morning

Sunny north, partly or mostly cloudy south.

Thursday Afternoon

Increasing clouds north to central, light snow south.

Thursday Night - Friday Morning

Mostly light snow.

Friday Afternoon

Light to moderate snow.

Mt. Hood Area
Date Weather
Thursday Morning

Increasing clouds.

Thursday Afternoon

Light to moderate snow.

Thursday Night - Friday Morning

Moderate to heavy snow.

Friday Afternoon

Moderate to heavy snow showers.

Snow Level/Freezing Level in feet

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Thursday Morning Freezing Level 0' 0' 0' 0' 0' *
Thursday Afternoon Snow Level 0' 0' 0' 0' 0' *
Thursday Night Snow Level 1000' 0' 0' 0' 1000' *
Friday Morning Snow Level 1500' 0' 0' 0' 2000' *
Friday Afternoon Snow Level 1500' 500' 0' 0' 3000' *
Olympics
Date Elevation
Thursday Morning Freezing Level
0'
Easterly Flow*
Thursday Afternoon Snow Level
0'
Easterly Flow*
Thursday Night Snow Level
1000'
Easterly Flow*
Friday Morning Snow Level
1500'
Easterly Flow*
Friday Afternoon Snow Level
1500'
Easterly Flow*
Friday Night Snow Level
2000'
Northwest Cascades
Date Elevation
Thursday Morning Freezing Level
0'
Easterly Flow*
Thursday Afternoon Snow Level
0'
Easterly Flow*
Thursday Night Snow Level
0'
Easterly Flow*
Friday Morning Snow Level
0'
Easterly Flow*
Friday Afternoon Snow Level
500'
Easterly Flow*
Friday Night Snow Level
1000'
Northeast Cascades
Date Elevation
Thursday Morning Freezing Level
0'
Easterly Flow*
Thursday Afternoon Snow Level
0'
Easterly Flow*
Thursday Night Snow Level
0'
Easterly Flow*
Friday Morning Snow Level
0'
Easterly Flow*
Friday Afternoon Snow Level
0'
Easterly Flow*
Friday Night Snow Level
0'
Central Cascades
Date Elevation
Thursday Morning Freezing Level
0'
Easterly Flow*
Thursday Afternoon Snow Level
0'
Easterly Flow*
Thursday Night Snow Level
0'
Easterly Flow*
Friday Morning Snow Level
0'
Easterly Flow*
Friday Afternoon Snow Level
0'
Easterly Flow*
Friday Night Snow Level
1500'
South Cascades
Date Elevation
Thursday Morning Freezing Level
0'
Easterly Flow*
Thursday Afternoon Snow Level
0'
Easterly Flow*
Thursday Night Snow Level
1000'
Easterly Flow*
Friday Morning Snow Level
2000'
Easterly Flow*
Friday Afternoon Snow Level
3000'
Easterly Flow*
Friday Night Snow Level
2000'

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 Fri Sat
Hurricane Ridge .25 .50
Mt Baker Ski Area .25 .75 - 1.00
Washington Pass lt .25 .50
Stevens Pass lt .25 .75
Snoqualmie Pass .25 .75 - 1.00
Mission Ridge .25 .25
Crystal Mt .25 .75
Paradise .50 1.00 - 1.50
White Pass .50 .50 - .75
Mt Hood Meadows .75 - 1.00 1.00

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

Date Direction - Speed
Thursday E 25 - 35
Thursday Night E 15 - 25
Friday E 5 - 15

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
Thursday Morning SE 10 - 20 SE 10 - 20 SE 15 - 25 SE 20 - 30
Thursday Afternoon SE 15 - 25 SE 10 - 20 SE 15 - 25 SE 20 - 30
Thursday Night SW 20 - 30 SSW 15 - 25 SSW 15 - 25 SW 25 - 35
Friday Morning SW 20 - 30 SSW 15 - 25 SSW 15 - 25 SW 25 - 35
Friday Afternoon SW 15 - 25 SSW 10 - 20 SSW 15 - 25 SW 25 - 35
Olympics
Date Elevation
Thursday Morning SE 10 - 20
Thursday Afternoon SE 15 - 25
Thursday Night SW 20 - 30
Friday Morning SW 20 - 30
Friday Afternoon SW 15 - 25
Friday Night SW 30 - 40
Northwest Cascades
Date Elevation
Thursday Morning SE 10 - 20
Thursday Afternoon SE 10 - 20
Thursday Night SSW 15 - 25
Friday Morning SSW 15 - 25
Friday Afternoon SSW 10 - 20
Friday Night SW 20 - 30
Central Cascades
Date Elevation
Thursday Morning SE 15 - 25
Thursday Afternoon SE 15 - 25
Thursday Night SSW 15 - 25
Friday Morning SSW 15 - 25
Friday Afternoon SSW 15 - 25
Friday Night SW 20 - 30
South Cascades
Date Elevation
Thursday Morning SE 20 - 30
Thursday Afternoon SE 20 - 30
Thursday Night SW 25 - 35
Friday Morning SW 25 - 35
Friday Afternoon SW 25 - 35
Friday Night SW 30 - 40
Olympics
Date Direction - Speed
Thursday Morning SE 10 - 20
Thursday Afternoon SE 15 - 25
Thursday Night SW 20 - 30
Friday Morning SW 20 - 30
Friday Afternoon SW 15 - 25
Friday Night SW 30 - 40
Northwest Cascades
Date Direction - Speed
Thursday Morning SE 10 - 20
Thursday Afternoon SE 10 - 20
Thursday Night SSW 15 - 25
Friday Morning SSW 15 - 25
Friday Afternoon SSW 10 - 20
Friday Night SW 20 - 30
Central Cascades
Date Direction - Speed
Thursday Morning SE 15 - 25
Thursday Afternoon SE 15 - 25
Thursday Night SSW 15 - 25
Friday Morning SSW 15 - 25
Friday Afternoon SSW 15 - 25
Friday Night SW 20 - 30
South Cascades
Date Direction - Speed
Thursday Morning SE 20 - 30
Thursday Afternoon SE 20 - 30
Thursday Night SW 25 - 35
Friday Morning SW 25 - 35
Friday Afternoon SW 25 - 35
Friday Night SW 30 - 40

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
Thursday Morning SE 10 - 20 SE 10 - 20 SE 15 - 25 SW 20 - 30
Thursday Afternoon SE 10 - 20 SE 15 - 25 SSE 20 - 30 SW 40 - 60
Thursday Night SW 30 - 40 SW 30 - 40 SW 35 - 45 SW 45 - 65
Friday Morning SW 35 - 45 SW 25 - 35 SW 40 - 60 SW 50 - 70
Friday Afternoon SW 25 - 35 SW 25 - 35 SW 40 - 60 SW 50 - 70
Northwest Cascades
Date Direction - Speed
Thursday Morning SE 10 - 20
Thursday Afternoon SE 10 - 20
Thursday Night SW 30 - 40
Friday Morning SW 35 - 45
Friday Afternoon SW 25 - 35
Friday Night SW 35 - 45
Northeast Cascades
Date Direction - Speed
Thursday Morning SE 10 - 20
Thursday Afternoon SE 15 - 25
Thursday Night SW 30 - 40
Friday Morning SW 25 - 35
Friday Afternoon SW 25 - 35
Friday Night SW 25 - 35
Central Cascades
Date Direction - Speed
Thursday Morning SE 15 - 25
Thursday Afternoon SSE 20 - 30
Thursday Night SW 35 - 45
Friday Morning SW 40 - 60
Friday Afternoon SW 40 - 60
Friday Night SW 50 - 70
South Cascades
Date Direction - Speed
Thursday Morning SW 20 - 30
Thursday Afternoon SW 40 - 60
Thursday Night SW 45 - 65
Friday Morning SW 50 - 70
Friday Afternoon SW 50 - 70
Friday Night SW 35 - 45

Directions above indicate the direction the wind blows from on the 16-point cardinal scale. These winds 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.

The Extended Mountain Weather Forecast (Days 3-5) will be included with the afternoon forecast issuance around 1:30 PM.