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Mountain Weather Forecast

Issued: 3:28 PM PST Wednesday, March 7, 2018
by Dennis D'Amico

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

Upper level ridging over the area will lead to one more dry day in the Pacific Northwest, however high clouds streaming up from the south will quickly create high overcast conditions for all areas by late morning to mid-day. Cold temperatures seen early this morning along the east slopes of the Cascades will rise with the rest of the area this afternoon. 

A low pressure system off the northern California coast will track northeast later tonight spreading very light rain and snow over the area with the initial frontal band. The air mass over our region is quite dry, so this first wave of moisture will do little other than bring cloud ceilings and snow levels down overnight. 

After a lull in the early morning, the real action should get started by late Thursday morning as the low pressure system tracks to north of the Olympic Peninsula and into southern B.C by early evening. Winds will ramp up quickly, especially in the alpine ahead of the frontal boundary that will pass through the Cascades late Thursday afternoon. The Olympics and the central and south Washington Cascades should see stormy conditions develop Thursday afternoon. Easterly flow through the Cascade Passes will initially keep snow levels suppressed through early afternoon, but snow levels should rise to the 3500-4000 feet by early afternoon with a bump to 4000-4500 in the late afternoon and early evening. 

Behind the front, post-frontal showers, windy conditions and a cooling trend should ensue Thursday night as the trailing longwave trough approaches the coastline. There may be a period of heavy showers at Mt. Baker Thursday evening.  

Weather forecast for Wednesday & Thursday

Olympics
Date Weather
Wednesday Mostly clear becoming cloudy late this morning or mid-day with high clouds. Mild.
Wednesday Night Cloudy with very light rain and snow developing. Clouds lowering.
Thursday Light rain and snow in the morning becoming light to moderate rain and snow in the afternoon. Winds increasing rapidly and peaking mid-day. Slight warming trend.
Light to occasionally moderate rain and snow showers. Windy. Cooling trend late.
Washington Cascades near and west of the Crest including Stevens, Snoqualmie and White Passes
Date Weather
Wednesday Mostly clear north, mostly cloudy south with high clouds. Becoming cloudy all areas with high clouds today. Mild.
Wednesday Night Cloudy with very light rain and snow developing after midnight. Clouds lowering.
Thursday Periods of light rain and snow in the morning becoming moderate rain and snow in the afternoon. Winds increasing rapidly, especially in the alpine in the central and south Cascades. Slight warming trend.
Light to moderate rain and snow showers, locally heavy Mt. Baker area in the evening. Windy. Cooling trend late.
East Slopes of the Washington Cascades
Date Weather
Wednesday Mostly clear northeast, mostly cloudy southeast with high clouds. Becoming cloudy all areas with high clouds today. Mild.
Wednesday Night Cloudy with very light rain and snow developing after midnight. Clouds lowering.
Thursday Periods of light rain and snow in the morning becoming light to moderate rain and snow in the afternoon. Winds increasing rapidly, especially in the alpine in the central-east and southeast Cascades. Slight warming trend.
Light to occasionally moderate rain and snow showers near the Cascade crest. Windy. Cooling trend late.
Mt. Hood
Date Weather
Wednesday Overcast with high clouds. Mild.
Wednesday Night Cloudy with very light rain and snow developing after midnight. Clouds lowering.
Thursday Periods of light rain and snow. Winds increasing rapidly.
Light to moderate rain and snow showers. Windy. Cooling trend late.

Snow Level/Freezing Level in feet

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Wednesday Afternoon Freezing Level 7500' 6500' 6000' 7000' 8000'
Wednesday Night Snow Level 4500' 4000' 2500' 3000' 5000' *
Thursday Morning Snow Level 4000' 3500' 3000' 3000' 5000' *
Thursday Afternoon Snow Level 4500' 4000' 4000' 4000' 5500' *
Thursday Evening Snow Level 4500' 4000' 4000' 4500' 5000'
Olympics
Date Elevation
Wednesday Afternoon Freezing Level
7500'
Wednesday Night Snow Level
4500'
Easterly Flow*
Thursday Morning Snow Level
4000'
Easterly Flow*
Thursday Afternoon Snow Level
4500'
Easterly Flow*
Thursday Evening Snow Level
4500'
Thursday Night Snow Level
2500'
Northwest Cascades
Date Elevation
Wednesday Afternoon Freezing Level
6500'
Wednesday Night Snow Level
4000'
Easterly Flow*
Thursday Morning Snow Level
3500'
Easterly Flow*
Thursday Afternoon Snow Level
4000'
Easterly Flow*
Thursday Evening Snow Level
4000'
Thursday Night Snow Level
2500'
Northeast Cascades
Date Elevation
Wednesday Afternoon Freezing Level
6000'
Wednesday Night Snow Level
2500'
Easterly Flow*
Thursday Morning Snow Level
3000'
Easterly Flow*
Thursday Afternoon Snow Level
4000'
Easterly Flow*
Thursday Evening Snow Level
4000'
Thursday Night Snow Level
3500'
Central Cascades
Date Elevation
Wednesday Afternoon Freezing Level
7000'
Wednesday Night Snow Level
3000'
Easterly Flow*
Thursday Morning Snow Level
3000'
Easterly Flow*
Thursday Afternoon Snow Level
4000'
Easterly Flow*
Thursday Evening Snow Level
4500'
Thursday Night Snow Level
3000'
South Cascades
Date Elevation
Wednesday Afternoon Freezing Level
8000'
Wednesday Night Snow Level
5000'
Easterly Flow*
Thursday Morning Snow Level
5000'
Easterly Flow*
Thursday Afternoon Snow Level
5500'
Easterly Flow*
Thursday Evening Snow Level
5000'
Thursday Night Snow Level
4000'

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 lt .10 .50 - .75
Mt Baker Ski Area lt .10 1.50 - 2.00
Washington Pass lt .10 .75
Stevens Pass lt .10 .75 - 1.00
Snoqualmie Pass lt .10 1.00 - 1.50
Mission Ridge lt .10 .25
Crystal Mt lt .10 1.00
Paradise lt .10 1.50 - 2.00
White Pass lt .10 1.00
Mt Hood Meadows lt .10 1.00

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

Date Direction - Speed
Wednesday Afternoon E 5 - 15
Wednesday Night E 10 - 20
Thursday Morning E 10 - 20
Thursday Afternoon E 0 - 10

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 S 0 - 10 S 5 - 15 ESE 10 - 20 SE 5 - 15
Wednesday Night S 15 - 25 SE 5 - 15 ESE 10 - 20 S 5 - 15
Thursday Morning S 30 - 40 SE 20 - 30 SE 15 - 30 SW 25 - 35
Thursday Afternoon SW 15 - 25 SSE 15 - 25 S 20 - 35 SW 40 - 50
Olympics
Date Elevation
Wednesday Afternoon S 0 - 10
Wednesday Night S 15 - 25
Thursday Morning S 30 - 40
Thursday Afternoon SW 15 - 25
Thursday Night SW 20 - 30
Northwest Cascades
Date Elevation
Wednesday Afternoon S 5 - 15
Wednesday Night SE 5 - 15
Thursday Morning SE 20 - 30
Thursday Afternoon SSE 15 - 25
Thursday Night SW 25 - 35
Central Cascades
Date Elevation
Wednesday Afternoon ESE 10 - 20
Wednesday Night ESE 10 - 20
Thursday Morning SE 15 - 30
Thursday Afternoon S 20 - 35
Thursday Night SW 30 - 40
South Cascades
Date Elevation
Wednesday Afternoon SE 5 - 15
Wednesday Night S 5 - 15
Thursday Morning SW 25 - 35
Thursday Afternoon SW 40 - 50
Thursday Night SW 30 - 40
Olympics
Date Direction - Speed
Wednesday Afternoon S 0 - 10
Wednesday Night S 15 - 25
Thursday Morning S 30 - 40
Thursday Afternoon SW 15 - 25
Thursday Night SW 20 - 30
Northwest Cascades
Date Direction - Speed
Wednesday Afternoon S 5 - 15
Wednesday Night SE 5 - 15
Thursday Morning SE 20 - 30
Thursday Afternoon SSE 15 - 25
Thursday Night SW 25 - 35
Central Cascades
Date Direction - Speed
Wednesday Afternoon ESE 10 - 20
Wednesday Night ESE 10 - 20
Thursday Morning SE 15 - 30
Thursday Afternoon S 20 - 35
Thursday Night SW 30 - 40
South Cascades
Date Direction - Speed
Wednesday Afternoon SE 5 - 15
Wednesday Night S 5 - 15
Thursday Morning SW 25 - 35
Thursday Afternoon SW 40 - 50
Thursday 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
Wednesday Afternoon SW 10 - 20 SW 10 - 20 SW 15 - 25 S 20 - 30
Wednesday Night SSW 15 - 30 S 15 - 25 SSW 20 - 30 S 25 - 35
Thursday Morning S 25 - 35 SW 15 - 25 SW 45 - 60 SW 55 - 65
Thursday Afternoon SSW 40 - 50 SSW 25 - 35 SW 55 - 70 SW 60 - 70
Northwest Cascades
Date Direction - Speed
Wednesday Afternoon SW 10 - 20
Wednesday Night SSW 15 - 30
Thursday Morning S 25 - 35
Thursday Afternoon SSW 40 - 50
Thursday Night SW 30 - 40
Northeast Cascades
Date Direction - Speed
Wednesday Afternoon SW 10 - 20
Wednesday Night S 15 - 25
Thursday Morning SW 15 - 25
Thursday Afternoon SSW 25 - 35
Thursday Night SW 35 - 45
Central Cascades
Date Direction - Speed
Wednesday Afternoon SW 15 - 25
Wednesday Night SSW 20 - 30
Thursday Morning SW 45 - 60
Thursday Afternoon SW 55 - 70
Thursday Night SW 45 - 55
South Cascades
Date Direction - Speed
Wednesday Afternoon S 20 - 30
Wednesday Night S 25 - 35
Thursday Morning SW 55 - 65
Thursday Afternoon SW 60 - 70
Thursday Night SW 45 - 55

Extended Weather Synopsis for Friday through Sunday

A sharp trough will pass through the Cascades Friday morning. Shower activity behind the trough should become scattered and quickly die down in the afternoon as upper level ridging builds offshore. A convergence zone may develop Friday morning in the Mountain Loop to Stevens Pass vicinity. Strong west winds on the east slopes of the Cascades will accompany the trough's passage in the morning.  Snow levels will be much cooler Friday. 

Upper level ridging passes inland Friday night with the flow aloft turning S-SW on Saturday.  Saturday's forecast looks mostly dry, but an embedded shortwave in the flow will likely bring some cloud cover and the chance of scattered showers between Saturday afternoon and night. 

The ridge should retrograde over the West Coast Sunday for a better bet of drier and warmer weather. 

Extended Weather Forecast for Friday through Sunday

Olympics, Washington Cascades and Mt. Hood Area
Date Weather
Friday Cloudy with light to occasionally moderate rain and snow showers, heaviest west slopes of the Cascades quickly decreasing in the afternoon. Windy East Slopes of the Cascades in the morning.
Friday Night Mostly to partly cloudy with isolated light rain and snow showers ending.
Saturday Partly cloudy with an increasing clouds in the afternoon. Chance of showers south Washington Cascades and Mt. Hood.
Saturday Night Mostly cloudy with a chance of showers.

Snow/Freezing Levels

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Friday Snow Level None' - None' None' - None' None' - None' None' - None' None' - None'
Friday Night Snow Level None' - None' None' - None' None' - None' None' - None' None' - None'
Saturday Snow Level None' - None' None' - None' None' - None' None' - None' None' - None'
Saturday Night Snow Level None' - None' None' - None' None' - None' None' - None' None' - None'
Olympics
Date Elevation
Friday Snow Level
None' - None'
Friday Night Snow Level
None' - None'
Saturday Snow Level
None' - None'
Saturday Night Snow Level
None' - None'
Sunday Snow Level
None' - None'
Northwest Cascades
Date Elevation
Friday Snow Level
None' - None'
Friday Night Snow Level
None' - None'
Saturday Snow Level
None' - None'
Saturday Night Snow Level
None' - None'
Sunday Snow Level
None' - None'
Northeast Cascades
Date Elevation
Friday Snow Level
None' - None'
Friday Night Snow Level
None' - None'
Saturday Snow Level
None' - None'
Saturday Night Snow Level
None' - None'
Sunday Snow Level
None' - None'
Central Cascades
Date Elevation
Friday Snow Level
None' - None'
Friday Night Snow Level
None' - None'
Saturday Snow Level
None' - None'
Saturday Night Snow Level
None' - None'
Sunday Snow Level
None' - None'
South Cascades
Date Elevation
Friday Snow Level
None' - None'
Friday Night Snow Level
None' - None'
Saturday Snow Level
None' - None'
Saturday Night Snow Level
None' - None'
Sunday Snow Level
None' - None'

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.