Mountain Weather Forecast
Northwest Weather and Avalanche Center Seattle Washington
702 AM PST Fri Mar 12 2010
The NWAC program is administered by the USDA-Forest Service and operates out of 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.
WAZ513-518-519-019-042-501-502-ORZ011
Weather Synopsis for Friday and Saturday
In the strong circulation around a deep upper low in the Gulf of Alaska, a strong front moved into the region Thursday morning, weakening and stalling over central WA Thursday afternoon and evening as several waves rotated around and into the base of the associated upper trough. One of these stronger waves developed a secondary frontal system that is spreading increasing rain or snow northeastward over the area early Friday morning along with brief but limited warming and a return to strong ridgetop winds, especially in the southern and central WA Cascades. Increasing moderate rain or snow Friday morning should slowly decrease and turn more showery Friday afternoon, along with rapidly lowering freezing levels but only slowly decreasing winds.
As the main energy with the following offshore trough dives southeastward into north-central CA, this should split and weaken the trough later Friday with a greatly weakened upper trough but moderate surface trough moving into the area late Friday night and Saturday morning for a brief increase in light to moderate showers at low and lowering freezing levels. Behind the trough passage later Saturday morning, decreasing light showers are likely mid-day and Saturday afternoon along with some brief partial clearing as initially flat but slowly strengthening upper ridging moves onshore. While showers should generally end later Saturday, the still flat but building upper ridge should allow considerable mid and upper level moisture to spread over the area ahead of a gradually deepening upper low in the Gulf of Alaska. This should maintain considerable mid and high cloudiness into Sunday along with low freezing levels and relatively light ridgetop winds.
Weather Forecast for Friday and Saturday
Olympics
| Time | Weather |
| Friday morning |
Moderate to occasionally heavy snow decreasing mid-day and becoming more showery |
| Friday afternoon |
Cool with light to moderate showers and some brief partial clearing |
| Friday night |
Light showers increasing late |
| Saturday morning |
Cool with light to occasionally moderate showers, heaviest west slopes |
| Saturday afternoon |
Light showers decreasing with partial clearing through increasing mid and high clouds |
| Saturday night | Continued cool with considerable mid and high clouds |
Washington Cascades near and west of the crest
| Time | Weather |
| Friday morning |
Very windy higher ridgetops with light to moderate rain or snow increasing and becoming moderate to occasionally heavy |
| Friday afternoon |
Cooler with moderate rain or snow decreasing and becoming showery; very slowly decreasing winds |
| Friday night |
Light to moderate snow showers increasing late, heaviest north |
| Saturday morning |
Light to moderate showers briefly increasing, then decreasing late |
| Saturday afternoon |
Partly cloudy with scattered light showers ending; variable high clouds increasing late |
| Saturday night | Variable mid and high clouds |
Cascade Passes, including Stevens, Snoqualmie and White Passes
| Time | Weather |
| Friday morning |
Windy higher ridgetops with light to moderate rain or snow increasing and becoming moderate to occasionally heavy |
| Friday afternoon |
Cooler with moderate rain or snow decreasing and becoming showery and mostly snow; slowly decreasing ridgetop winds |
| Friday night |
Light to moderate snow showers increasing late, heaviest north |
| Saturday morning |
Light to moderate snow showers briefly increasing, then decreasing late |
| Saturday afternoon |
Partly cloudy with scattered light showers ending; variable high clouds increasing late |
| Saturday night | Variable mid and high clouds |
East slopes Washington Cascades
| Time | Weather |
| Friday morning |
Windy higher ridgetops with light rain or snow increasing and becoming moderate |
| Friday afternoon |
Cooler with light to occasionally moderate rain or snow decreasing and becoming showery and mostly snow, mainly higher terrain near the crest with some partial clearing lower elevations; slowly decreasing ridgetop winds |
| Friday night |
Light snow showers increasing late, heaviest north |
| Saturday morning |
Light to occasionally moderate snow showers briefly increasing, then decreasing late |
| Saturday afternoon |
Partly cloudy with scattered light showers ending; variable high clouds increasing late |
| Saturday night | Variable mid and high clouds |
Mt Hood area
| Time | Weather |
| Friday morning |
Windy higher ridgetops with light to moderate rain or snow increasing and becoming moderate to occasionally heavy |
| Friday afternoon |
Cooler with moderate rain or snow decreasing and becoming showery and mostly snow; very slowly decreasing ridgetop winds |
| Friday night |
Light to occasionally moderate snow showers |
| Saturday morning |
Light to occasionally moderate snow showers decreasing late |
| Saturday afternoon |
Partly cloudy with scattered light showers ending; variable high clouds increasing late |
| Saturday night | Variable high clouds |
Snow Level/Freezing Level Trends in feet
Snow Levels in feet
Olympics
| Time | Elevation |
| Friday early morning |
2500 |
| Friday late morning |
3000 |
| Friday afternoon through Saturday morning |
2000 |
| Saturday afternoon |
2500 |
| Saturday night |
2000 |
West Slopes Cascades--Mt Baker (N) to Mt Hood (S)
| Time | North | Central | South |
| Friday early morning |
3000 |
4500 |
5000 |
| Friday late morning |
3500 |
4000 |
4000 |
| Friday afternoon |
2000 |
2500 |
2500 |
| Friday night |
1500 |
1500 |
1500 |
| Saturday morning |
2000 |
2000 |
2000 |
| Saturday afternoon | 2000 | 2500 | 2500 |
| Saturday night | 2000 | 2000 | 2000 |
Cascade Passes including East Slopes Washington Cascades
| Time | North | Central | South |
| Early Friday morning |
3000 |
3000 |
4500 |
| Late Friday morning |
3500 |
3500 |
3500 |
| Friday afternoon |
2000 |
2500 |
2500 |
| Friday night |
1500 |
1500 |
1500 |
| Saturday morning |
2000 |
2000 |
2000 |
| Saturday afternoon | 2000 | 2500 | 2500 |
| Saturday night | 2000 | 2000 | 2000 |
Cascade Snow / Freezing Levels noted above refer to the north (approximately Mt Baker and Washington Pass), central (approximately Stevens and Snoqualmie Pass) and south (near Mt Hood). Note that surface snow levels are common near the passes during easterly pass flow and may result in multiple snow / freezing levels.
Quantitative Precipitation
24 hour forecast of precipitation in inches of water (rain) equivalent ending at 4AM of indicated day
| Location | Saturday | Sunday |
| Hurricane Ridge | .5-.75 |
LT .25 |
| Mt Baker | .75 |
.25-.5 |
| Washington Pass | .5 |
LT .25 |
| Stevens Pass | .75 |
LT .25 |
| Snoqualmie Pass | .75 |
LT .25 |
| Mission Ridge | .25-.5 |
LT .25 |
| Crystal Mt | .75 |
LT .25 |
| Paradise | .75-1 |
LT .25 |
| White Pass | .5-.75 |
LT .25 |
| Mt Hood | .5-.75 |
LT .25 |
LT = less than; WE or Water equivalent is the liquid water equivalent of melted snow in hundredths of inches. As a rough approximation 1 inch of snow = about .10 inches WE, or 10 inches of snow = about 1 inch WE.
Winds in Miles per Hour (MPH) "Cascade Pass Level Winds"
| Time | Direction | Speed |
| Friday morning |
E |
5-15 |
| Friday mid-day | W |
5-10 |
| Friday afternoon | W |
10-15 |
| Friday night | E |
5-15 |
| Saturday morning | W |
10-20 with occasional higher gusts |
| Saturday afternoon | W |
5-15 |
| Saturday night | W |
0-10 |
| Early Sunday | 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 FT (in Miles per Hour (MPH))
| Time | Olympics | North | Central | South |
| Friday morning | SSW 10-20 |
SSW 10-20 | SSW 20-40 |
SSW 30-50 |
| Late Friday morning |
SSW 20-40 |
SSW 20-40 |
SSW 20-40 |
SSW 20-40 |
| Friday afternoon |
SW 30-50 |
SW 20-40 |
SW 20-40 |
SW 20-40 |
| Friday night |
WSW 30-45 |
SW 30-50 |
SW 30-50 |
SW 20-40 |
| Saturday morning |
WSW 15-30 |
WSW 20-40 |
WSW 20-40 |
WSW 20-40 |
| Saturday mid-day |
WSW 15-25 |
WSW 15-25 |
WSW 15-25 |
WSW 15-25 |
| Saturday afternoon | SW 15-25 | SW 10-20 | SW 10-20 | SW 10-20 |
| Saturday night | SSW 20-40 | SSW 10-20 | SSW 10-20 | SSW 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 FT (in Miles per Hour (MPH))
| Time | Olympics | North | Central | South |
| Friday morning | SW 20-40 | SW 20-40 |
SW 40-60 |
SW 40-60 |
| Friday mid-day |
SSW 25-40 |
SSW 25-40 |
SSW 30-50 |
SSW 30-50 |
| Friday afternoon |
SSW 30-50 |
SSW 30-45 |
SSW 30-45 |
SSW 30-45 |
| Friday night |
WSW 20-40 |
WSW 30-45 |
WSW 30-45 |
WSW 30-45 |
| Saturday morning |
WNW 20-30 |
W 15-30 |
W 20-40 |
W 20-40 |
| Saturday mid-day | W 15-25 | W 15-25 | WNW 15-25 | WNW 15-25 |
| Saturday afternoon |
SW 15-25 |
SW 10-20 | SW 10-20 |
SW 10-20 |
| Saturday night | SW 15-25 | SW 15-25 | SW 15-25 | SW 15-25 |
Extended Weather Synopsis for Sunday through Tuesday
As several short waves rotate around and into the base of a deep offshore trough, this should help to build weak upper ridging over or just east of the Cascades Sunday into Monday morning, with an incoming front stalling and weakening along the coast. With a relatively dirty ridge and several impulses moving along the back edge of the front and intermittently edging it eastward, this should result in mostly cloudy skies in the Olympics and the northern Cascades along with occasional light rain or snow and moderate ridgetop winds at slowly rising freezing levels. However, in the southern and central WA Cascades and the Mt Hood area, the effects of the impulses should be less with partly cloudy skies (mainly mid or high clouds) amid a few scattered light showers and gradual warming. While a weak and slightly cooler easter surface flow is expected across the Cascade passes Sunday into Monday, it should provide only limited insulation from the gradual warming aloft, especially during the mid-day and afternoon hours when solar effects may be significant.
As the front slowly nudges eastward mid-late Monday, light rain or snow should gradually increase in the Olympics and northern WA Cascades with increasing clouds and occasional light rain or snow spreading into the southern and central Cascades and Mt Hood area later Monday. This should be accompanied by further rising freezing levels and gradually increasing ridgetop winds, especially in the Olympics and north-central WA Cascades. Increasing light to moderate rain or snow, rapid cooling and moderate to strong winds are expected early to mid Tuesday as the front finally moves through the area. This should be followed by several weak upper troughs that should maintain light to moderate showers at relatively low freezing levels later Tuesday into Wednesday.
Extended Weather Forecast for Sunday through Tuesday
Olympics, West Slopes Washington Cascades & Mt Hood Area
| Time | Weather |
| Sunday and Sunday night |
Olympics and N WA Cascades: Partly to mostly cloudy with occasional light rain or snow developing later Sunday Central and southern WA Cascades, Mt Hood area: Considerable mid and high clouds with some filtered sunshine |
| Monday |
Olympics and N WA Cascades: Mostly cloudy and warmer with occasional light rain or snow Central and southern WA Cascades, Mt Hood area: Warmer with considerable mid and high clouds increasing and some light showers developing |
| Monday night and Tuesday morning |
Light rain or snow increasing Olympics and N WA Cascades and spreading to remainder Cascades overnight; Windy with moderate rain or snow Tuesday morning |
| Tuesday afternoon and night |
Cooler with moderate snow showers |
Cascade Passes
| Time | Weather |
| Sunday and Sunday night |
N Cascades: Partly to mostly cloudy with occasional light rain or snow developing later Sunday Central and southern Cascades: Considerable mid and high clouds with some filtered sunshine |
| Monday |
N Cascades: Mostly cloudy and a little warmer with occasional light rain or snow; increasing temperature inversion Central and southern Cascades: Warmer with considerable mid and high clouds increasing and some light showers developing; increasing temperature inversion |
| Monday night and Tuesday morning |
Light rain or snow N Cascades increasing and spreading to remainder Cascades overnight; Windy with moderate rain or snow Tuesday morning |
| Tuesday afternoon and night |
Cooler with moderate snow showers |
East Slopes Washington Cascades
| Time | Weather |
| Sunday and Sunday night |
N Cascades: Partly to mostly cloudy with occasional light rain or snow developing higher terrain near the crest later Sunday Central and southern Cascades: Considerable mid and high clouds with some filtered sunshine |
| Monday |
N Cascades: Mostly cloudy and a little warmer with occasional light rain or snow; increasing temperature inversion Central and southern Cascades: Warmer with considerable mid and high clouds increasing and some light showers developing; increasing temperature inversion |
| Monday night and Tuesday morning |
Light rain or snow N Cascades increasing and spreading to remainder Cascades overnight; Windy with moderate rain or snow Tuesday morning |
| Tuesday afternoon and night |
Cooler with moderate snow showers |
Extended Forecast for Sunday through Tuesday ("Snow Levels")
Snow Levels in Feet
Olympics and West Slopes Cascades--Mt Baker (N) to Mt Hood (S)
| Time | North | Central | South |
| Sunday morning |
1-2000 |
1-2500 |
1500-3000 |
| Sunday afternoon and night |
2-4000 |
3-5000 |
5-7000 |
| Monday and Monday night |
5-7000 |
5-7000 |
6-8000 |
| Tuesday morning |
4-6000 |
4-6000 |
5-7000 |
| Tuesday afternoon |
2-4000 |
2-4000 |
2-4000 |
| Tuesday night |
1-3000 |
1-3000 |
1500-3000 |
Cascade Passes and East Slopes Washington Cascades
| Time | North | Central | South |
| Sunday morning |
1-2000 |
1-2500 |
1500-3000 |
| Sunday afternoon and night |
2-4000 |
3-5000 |
4-6000 |
| Monday and Monday night |
4-5000 |
4-5000 |
5-6000 |
| Tuesday morning |
3-5000 |
3-5000 |
3-5000 |
| Tuesday afternoon |
2-4000 |
2-4000 |
2-4000 |
| Tuesday night |
1-3000 |
1-3000 |
1500-3000 |
NWAC weather data and forecasts are also available by calling 206-526-6677 for Washington, 503-808-2400 for the Mt Hood area, or by visiting our Web site at www.nwac.us. Remember that these avalanche forecasts apply to back country avalanche terrain below 7000 feet outside of developed and operating ski areas or highways.
The NWAC program is administered by the USDA-Forest Service. NWAC forecasts, data and avalanche or mountain weather information are made possible by partnerships between the Forest Service and many important cooperators, including the National Weather Service, Washington State Department of Transportation, Washington State Parks and Recreation Commission, Washington Snowparks and Snowmobile Grants, National Park Service, Ski Washington, Pacific Northwest Ski Area Association, the Friends of the Avalanche Center and others.
This forecast is prepared for cooperators and users of the NWAC, as an aide to tranportation and recreational operations, and to help promote public safety in the NW mountains.
Moore/Northwest Weather and Avalanche Center Seattle Washington