Mountain Weather Forecast
Northwest Weather and Avalanche Center Seattle Washington
1431 PM PST Fri Nov 20 2009
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.
WAZ-513-518-519-018-042-501-502-ORZ-011
Weather Synopsis for Friday and Saturday
An upper level trough of low pressure is moving onto the coast Friday afternoon while the associated cold front has already cleared the Cascade crest near midday. The heaviest precipitation is moving inland to the south of the forecast area, however there are many areas receiving moderate showers Friday afternoon. Freezing levels peaked overnight and early Friday and have lowered significantly behind the frontal passage Friday afternoon. The temperature at the top of Crystal Mountain has cooled 8 degrees over the past three hours!
Freezing levels should continue to lower through the day Friday as the trough moves across the area.
With the trough passage we should see an increase in westerly flow and enhanced showers overnight through early Saturday.
The next approaching system should be right on the heels of the upper trough that moves east by early Saturday. Though the timing now appears to be a bit slower than earlier forecast. This next frontal disturbance should spread increasing precipitation over the region by Saturday afternoon and increase Saturday evening and night. With cool air in place Saturday and only slight rises in freezing levels expected, this should maintain relatively low freezing levels to maintain precipitation in the form of snow below the lowest pass level.
The heaviest forcing, greatest precipitation and strongest winds with the system late Saturday and Saturday night should be directed towards Mt Hood and the southern Washington Cascades, as Mt Baker shares the love!
Weather Forecast for Friday and Saturday
Olympics
| Time | Weather |
| Friday afternoon/night | Moderate snow showers decreasing becoming light |
| Saturday morning | Light snow developing |
| Saturday afternoon/night | Increasing moderate to occasionally heavy snow, changing to showers late night |
Washington Cascades near and west of the crest
Stevens, Snoqualmie and White Passes
| Time | Weather |
| Friday afternoon/night | Moderate snow showers, possibly enhanced near Stevens Pass in convergence overnight |
| Saturday morning | Light snow developing late morning or midday |
| Saturday afternoon/night | Increasing moderate to occasionally heavy snow, changing to showers late night |
East slopes Washington Cascades
| Time | Weather |
| Friday afternoon/night | Light snow showers decreasing with further cooling |
| Saturday | Cloudy with light snow developing midday |
| Saturday afternoon/night | Increasing light to occasionally moderate snow changing to showers overnight |
Mt Hood area
| Time | Weather |
| Friday afternoon/night | Periods of moderate snow showers |
| Saturday morning | Light snow developing late morning or midday |
| Saturday afternoon/night | Increasing moderate to heavy snow Saturday afternoon. Snow increasing becoming heavy snow overnight |
Snow Level/Freezing Level Trends in feet
Snow Levels in feet
Olympics
| Time | Elevation |
| Friday afternoon and night | 2500 |
| Saturday morning | 2000 |
| Saturday afternoon and night | 2500 |
Cascades--Mt Baker (N) to Mt Hood (S)
| Time | North | Central | South |
| Friday afternoon |
2000 | 2500 | 2500 |
| Friday night and Saturday morning | 1500 | 2000 | 2000 |
| Saturday afternoon and night | 2000 | 2500 | 3000 |
Remaining near the surface Cascade passes and east slopes through Friday morning, becominig free air levels later Friday morning through night.
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 | Sat |
Sun |
| Hurricane Ridge | .5-.75 | .75-1 |
| Mt Baker | 1 | 1-1.5 |
| Washington Pass | .5 | .5-.75 |
| Stevens Pass | .5 | 1 |
| Snoqualmie Pass | .75 | 1-1.5 |
| Mission Ridge | .25-.5 | .25-.5 |
| Crystal Mt | .5-.75 | 1 |
| Paradise | .5-.75 | 1.5 |
| White Pass | .5-.75 | 1-1.5 |
| Mt Hood | .75 | 1.5 |
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 afternoon and night | W | 10-20 |
| Saturday | W | 0-10 |
| Saturday afternoon and night | E | 0-10 |
Directions above indicate the direction the wind blows from on the 16-point cardinal scale.
Free Winds at 5000 FT (in Miles per Hour (MPH))
| Time | Olympics | North | South |
| Friday afternoon and night | WSW 30 |
SW 25 |
W 30 |
| Saturday morning | SW 30 | SW 20 | WSW35 |
| Saturday afternoon/evening | SSW 50 | SSW 40 | SW 35 |
| Saturday night | WSW 20 | SW 25 | SW 50 |
Free Winds at 9000 FT (in Miles per Hour (MPH))
| Time | Olympics | North | South |
| Friday afternoon and night | WSW 35 |
SW 30 |
W 30 |
| Saturday morning | SW 30 | SW 25 | W 35 |
| Saturday afternoon/evening | SSW 60 | SSW 45 | SW 30 |
| Saturday night | WSW 30 | SW 35 | SW 70 |
Extended Weather Synopsis for Sunday through Tuesday
Cool showery northwest flow is expected early Sunday, following a strong cold frontal passage late Saturday. This should maintain light to moderate snow showers at low freezing levels along the west slope areas early Sunday. Showers should taper off later Sunday as weak high pressure begins to build over the region.
A slowly building upper level ridge of high pressure is expected along the offshore waters by Monday. The ridge is not expected to be strong enough to produce clear skies, so clouds and possibly a little light precipitation may flow over the flat ridge Monday to affect mainly the Olympics and north part.
A weak to moderate strength disturbance is now expected to move through the ridge later Monday. This should cause increasing light to moderate rain or snow at significantly rising freezing levels later Monday.
Stronger high pressure should rebuild over the region Tuesday to cause drying and partial clearing at continued high freezing levels.
Extended Weather Forecast for Sunday through Tuesday
Olympics, Washington Cascades, Mt Hood Area
| Time | Weather |
| Sunday |
Moderate snow showers early, heaviest near and west of the crest. Decreasing occasional light snow showers Sunday night |
| Monday | Increasing moderate rain or snow and warming |
| Tuesday | Mostly cloudy north part with a chance of light rain. Partly cloudy and mild central and south part. |
Extended Forecast for Sunday through Tuesday ("Snow Levels")
Snow Levels in Feet
| Time | Olympics, North Cascades | South Cascades and Mt Hood |
| Sunday: |
1-2000 |
1-2000 |
| early Monday |
2-3000 |
3-4000 |
| late Monday | 5-6000 | 6-7000 |
| Tuesday | 6-7000 | 7-8000 |
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.
Kramer/Northwest Weather and Avalanche Center Seattle Washington