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Mountain Weather Forecast

Issued: 2:18 PM PST Monday, February 20, 2017
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 Monday & Tuesday

A low pressure system located off the central Oregon coast earlier this morning is tracking NE across the southern Washington Cascades today. The precipitation shield associated with a warm front has spread north into the central Washington Cascades through mid-day, but continues to only lightly brush the Olympics and north Cascades. 

Precipitation, winds and a warming trend will be most significant in the Mt. Hood area and south Washington Cascades on Monday although all areas are seeing a slight bump in snow levels. Mt. Hood may see snow levels bump up to 5000-5500 ft by late morning while they are in the warm sector before they slowly start to cool this afternoon. A switch to westerly winds will occur everywhere as the low passes to the east side of the Cascades this afternoon. 

Showers should ease later tonight before another low pressure system develops off the Oregon Coast and tracks to the NE on Tuesday.  Most forecast models have this low tracking further south and mainly affecting Mt. Hood.  However, the European model moves the precipitation shield further north, similar to Monday's system. The Day 2 precipitation forecast reflects the GFS/WRF track for now. 

A cold upper level trough is forecast to move over PNW starting Tuesday afternoon and snow levels should begin to drop in earnest later Tuesday afternoon into Tuesday night with light snow showers continuing overnight.  

Weather forecast for Monday & Tuesday

Olympics
Date Weather
Monday

Periods of light rain and snow developing in the morning becoming light rain and snow showers in the afternoon. Slight warming trend peaking in the early afternoon.  

Monday Night

Mostly cloudy with scattered light showers. 

Tuesday

Cloudy with ceilings lowering in the afternoon. Periods of very light rain and snow developing mid-day.  

Washington Cascades near and west of the crest including Stevens, Snoqualmie, and White Passes
Date Weather
Monday Afternoon - Monday Evening

Moderate rain and snow south Cascades. Light to occasionally moderate rain and snow in the central Cascades. Periods of light snow in the north Cascades. All steady precipitation becoming showers in the afternoon. Slight warming trend peaking in the afternoon. Strong alpine winds south Washington Cascades. 

Monday Night

Mostly cloudy with scattered light showers. 

Tuesday

Cloudy with ceilings lowering in the afternoon. Periods of light rain and snow developing mid-day, mainly central and south Cascades.  

East slopes of the Washington Cascades
Date Weather
Monday Afternoon - Monday Evening

Light to moderate rain and snow southeast and central-east Cascades becoming showers in the afternoon. Light rain northeast Cascades becoming showers in the afternoon. Slight warming trend peaking in the afternoon. Strong alpine winds southeast Washington Cascades. 

Monday Night

Mostly cloudy with isolated light showers. 

Tuesday

Cloudy with ceilings lowering in the afternoon. Periods of light rain and snow developing mid-day, mainly central-east and southeast Cascades.  

Mt. Hood Area
Date Weather
Monday Afternoon - Monday Evening

Light to moderate rain and snow becoming showers in the afternoon. Strong alpine winds. 

Monday Night

Mostly cloudy with scattered light showers. 

Tuesday

Light to occasionally moderate rain and snow.  

Snow Level/Freezing Level in feet

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Monday Afternoon Snow Level 4500' 4000' 4000' 3500' 4500'
Monday Night - Tuesday Morning Snow Level 2500' 2000' 1500' 2500' 4000'
Tuesday Afternoon Snow Level 3000' 2500' 3500' 3000' 3500'
Olympics
Date Elevation
Monday Afternoon Snow Level
4500'
Monday Night - Tuesday Morning Snow Level
2500'
Tuesday Afternoon Snow Level
3000'
Tuesday Night Snow Level
1000'
Northwest Cascades
Date Elevation
Monday Afternoon Snow Level
4000'
Monday Night - Tuesday Morning Snow Level
2000'
Tuesday Afternoon Snow Level
2500'
Tuesday Night Snow Level
1000'
Northeast Cascades
Date Elevation
Monday Afternoon Snow Level
4000'
Monday Night - Tuesday Morning Snow Level
1500'
Tuesday Afternoon Snow Level
3500'
Tuesday Night Snow Level
500'
Central Cascades
Date Elevation
Monday Afternoon Snow Level
3500'
Monday Night - Tuesday Morning Snow Level
2500'
Tuesday Afternoon Snow Level
3000'
Tuesday Night Snow Level
1000'
South Cascades
Date Elevation
Monday Afternoon Snow Level
4500'
Monday Night - Tuesday Morning Snow Level
4000'
Tuesday Afternoon Snow Level
3500'
Tuesday Night Snow Level
1500'

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

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

Date Direction - Speed
Monday Mid-day E 10 - 20
Monday Afternoon - Monday Evening W 10 - 20
Monday Night - Tuesday Morning 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
Monday Afternoon W 5 - 15 W 0 - 10 W 5 - 15 WSW 25 - 40
Monday Night - Tuesday Morning N 0 - 10 VAR 0 - 10 VAR 0 - 10 E 0 - 10
Olympics
Date Elevation
Monday Afternoon W 5 - 15
Monday Night - Tuesday Morning N 0 - 10
Tuesday Afternoon - Tuesday Night NW 10 - 20
Northwest Cascades
Date Elevation
Monday Afternoon W 0 - 10
Monday Night - Tuesday Morning VAR 0 - 10
Tuesday Afternoon - Tuesday Night W 5 - 15
Central Cascades
Date Elevation
Monday Afternoon W 5 - 15
Monday Night - Tuesday Morning VAR 0 - 10
Tuesday Afternoon - Tuesday Night WNW 5 - 15
South Cascades
Date Elevation
Monday Afternoon WSW 25 - 40
Monday Night - Tuesday Morning E 0 - 10
Tuesday Afternoon - Tuesday Night NW 20 - 30
Olympics
Date Direction - Speed
Monday Afternoon W 5 - 15
Monday Night - Tuesday Morning N 0 - 10
Tuesday Afternoon - Tuesday Night NW 10 - 20
Northwest Cascades
Date Direction - Speed
Monday Afternoon W 0 - 10
Monday Night - Tuesday Morning VAR 0 - 10
Tuesday Afternoon - Tuesday Night W 5 - 15
Central Cascades
Date Direction - Speed
Monday Afternoon W 5 - 15
Monday Night - Tuesday Morning VAR 0 - 10
Tuesday Afternoon - Tuesday Night WNW 5 - 15
South Cascades
Date Direction - Speed
Monday Afternoon WSW 25 - 40
Monday Night - Tuesday Morning E 0 - 10
Tuesday Afternoon - Tuesday Night NW 20 - 30

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
Monday Afternoon W 10 - 20 W 10 - 20 WSW 25 - 35 SW 50 - 70
Monday Night - Tuesday Morning SW 10 - 20 SW 0 - 10 SW 5 - 15 SSW 10 - 20
Tuesday Afternoon W 10 - 20 W 5 - 15 NW 15 - 25 NW 25 - 35
Northwest Cascades
Date Direction - Speed
Monday Afternoon W 10 - 20
Monday Night - Tuesday Morning SW 10 - 20
Tuesday Afternoon W 10 - 20
Tuesday Night W 15 - 25
Northeast Cascades
Date Direction - Speed
Monday Afternoon W 10 - 20
Monday Night - Tuesday Morning SW 0 - 10
Tuesday Afternoon W 5 - 15
Tuesday Night W 20 - 30
Central Cascades
Date Direction - Speed
Monday Afternoon WSW 25 - 35
Monday Night - Tuesday Morning SW 5 - 15
Tuesday Afternoon NW 15 - 25
Tuesday Night W 25 - 35
South Cascades
Date Direction - Speed
Monday Afternoon SW 50 - 70
Monday Night - Tuesday Morning SSW 10 - 20
Tuesday Afternoon NW 25 - 35
Tuesday Night W 30 - 40

Extended Weather Synopsis for Wednesday through Friday

A cold upper level trough will settle over the Pacific Northwest Wednesday and Thursday. The air mass will be marginally unstable on Wednesday. While precipitation amounts don't look overly impressive, heavier convective showers are possible in the afternoon. On Thursday, showers should be more isolated in nature and increase slightly in the afternoon with day-time warming. By Friday, an upper level low tracking south in the northerly branch of the jet stream should dig off the Washington coast. Shower activity is more likely for the Olympics, closer to the upper low with less clouds and shower coverage over the Cascades. Snow levels will remain low through the extended.  

Extended Weather Forecast for Wednesday through Friday

Olympics, Washington Cascades and Mt. Hood
Date Weather
Wednesday - Wednesday Night

Cloudy with light snow showers. Showers may become occasionally moderate in the afternoon. Colder. 

Thursday - Thursday Night

Partly to mostly cloudy with isolated snow showers mainly in the afternoon. 

Snow/Freezing Levels

Date Olympics Northwest Cascades Northeast Cascades Central Cascades South Cascades Easterly Flow in Passes
Wednesday Snow Level 1000' - 2000' 1000' - 2000' 1000' - 2000' 1000' - 2000' 1500' - 2500'
Olympics
Date Elevation
Wednesday Snow Level
1000' - 2000'
Wednesday Night - Friday Snow Level
500' - 1500'
Northwest Cascades
Date Elevation
Wednesday Snow Level
1000' - 2000'
Wednesday Night - Friday Snow Level
500' - 1500'
Northeast Cascades
Date Elevation
Wednesday Snow Level
1000' - 2000'
Wednesday Night - Friday Snow Level
500' - 1500'
Central Cascades
Date Elevation
Wednesday Snow Level
1000' - 2000'
Wednesday Night - Friday Snow Level
500' - 1500'
South Cascades
Date Elevation
Wednesday Snow Level
1500' - 2500'
Wednesday Night - Friday Snow Level
500' - 1500'

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.