Backcountry Avalanche Forecast
White Pass
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 variety of federal, state and private cooperators.
Weather Service ID WAZ513-518-519-019-042-501-502-ORZ011
| Thursday | Friday | Saturday | ||||||
| WARNING | ||||||||
| 6am-Noon | Noon-6pm | 6am-Noon | Noon-6pm | 6am-Noon | Noon-6pm | |||
| Danger Trend | Strongly Increasing | Strongly Increasing | Strongly Increasing | Slightly Decreasing | Level | Slightly Decreasing | ||
| 7000' | 4 | 4 | 4 | 4 | 3 | 3 | ||
| 6000' | 4 | 4 | 4 | 4 | 3 | 3 | ||
| 5000' | 3 | 4 | 4 | 4 | 3 | 3 | ||
| 4000' | 3 | 3 | 4 | 3 | 2 | 2 | ||
| 3000' | 3 | 3 | 4 | 3 | 2 | 2 | ||
| Notes: This represents a regional scale avalanche forecast for each elevation and time period shown. For complete information see the detailed avalanche forecast. | ||||||||
Jump to Danger Scale Legend at bottom of forecast
Forecast
AVALANCHE WARNING FOR LATE THURSDAY THR0UGH FRIDAY MORNING
Thursday: Considerable avalanche danger above 5 to 6000 feet and moderate below increasing Thursday morning and becoming high above 4 to 5000 feet and considerable below Thursday afternoon.
Thursday night and Friday: Further increasing avalanche danger becoming briefly high below 7000 feet Friday morning. Slowly decreasing danger expected Friday afternoon and night.
Saturday outlook: Considerable avalanche danger above 4 to 5000 feet and moderate below slowly decreasing
Snowpack Analysis
Increasing amounts of wind driven snow at slowly rising freezing levels have been deposited over a variety of buried weak layers early to mid Thursday morning, with an inch or two up to around 7 inches of new increasingly dense wind slab already being reported in some areas as of 9 to 10 AM. While intermittent light snowfall at low freezing levels this past week interspersed with some sunshine produced a highly variable snow surface ranging from thin to thick crusts, surface hoar to "dust on crust" up to about a foot of low density snow over an old slightly faceting crust (depending on location, aspect and elevation), the most important old weak layers prior to the onset of the current storm include very low density snow (fluff), spotty surface hoar, and a slightly faceting old crust. This developing unstable snow structure is producing a significant danger increase Thursday morning as slowly thickening and increasingly sensitive wind slabs should gradually spread to lower elevations, especially on northwest through northeast exposures.
Detailed Forecasts
Thursday
A strong front is spreading increasing moderate rain or snow over most areas Thursday morning, along with increasing ridgetop winds and slight warming. This should be followed by periods of moderate to occasionally heavy rain or snow and continued strong winds mid-day and Thursday afternoon along with further slight warming. With a variety of buried weak layers already in place, a resulting substantial increase in the avalanche danger is expected, with dangerous avalanche conditions developing on most lee slopes, especially northwest through northeast facing slopes which should receive most wind transport and where the most fragile old weak layers exist. Whumpfing, shooting cracks and remotely triggered and/or sympathetic avalanches are possible especially in shaded pockets where recent surface hoar was buried intact. Along with sensitive cornices that could easily fail through human triggers and an increasing likelihood of thickening 1 to 2 ft slabs releasing on buried weaknesses, careful snowpack evaluation, cautious routefinding and conservative decsion making should become increasingly essential on Thursday in order to avoid avalanche involvement.
Thursday night and Friday morning
After the first front stalls and weakens over central WA late Thursday, a second frontal wave should spread further moderate to heavy rain or snow northward late Thursday night and Friday morning, along with further slight warming and another surge of strong winds. This weather should produce a further danger increase, and generally high avalanche danger in many areas through development of a further upside-down and hollow feeling structure in the upper part of the snowpack. Natural and human triggered avalanches should become increasingly likely on steeper lee slopes, with some slab depths possibly reaching 2 to 4 ft or more in some heavily wind loaded terrain. As a result, back country travel in avalanche terrain is not recommended. Safest travel should be on windward ridges or lower angle terrain without steeper terrain above.
Friday afternoon through Saturday night
Moderate to heavy rain or snow should decrease and become mostly light to occasionally moderate snow showers Friday afternoon through Saturday morning along with gradually decreasing winds and substantial cooling. Associated slow settlement of recent snow should combine with previous avalanche activity and decreasing load to allow for a slow decrease in the danger, especially at lower elevations where some wet surface snow should refreeze and strengthen. However, expected cold temperatures and continued wind transport should allow for only a slight decrease in the danger on lee slopes near higher ridgelines...mainly north, northeast and east exposures. As a result, continued careful snowpack evaluation and cautious routefinding are urged, and conservative decision making is still strongly encouraged on slopes not experiencing stabilization through recent avalanche releases.
With the exception of a local slight increase in the danger on south facing slopes receiving sun breaks Saturday afternoon (where some loose or isolated slabs may be triggered by solar warming), scattered light showers, partial clearing and further diminishing winds Saturday afternoon and night should allow for a further slow decrease in the danger on more shaded lee terrain as recent active wind slabs continue to slowly settle and strengthen.
Danger Scale Legend
| 5 | = Extreme avalanche danger | |
| 4 | = High avalanche danger | |
| 3 | = Considerable avalanche danger | |
| 2 | = Moderate avalanche danger | |
| 1 | = Low avalanche danger | |
Warning = Extreme or high avalanche danger occurring or expected to occur within 12 hours: at or below 4000 feet in the Olympics and/or WA Cascades; at or below 5000 feet in the Mt. Hood Area.
Watch = Warning conditions expected within 12-48 hours.
Special Conditions = Unusual conditions meriting special attention that do not meet Watch or Warning criteria.
Click here for complete definitions of the avalanche danger scale.
Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone between dangers exists. Remember there are avalanche safe areas in the mountains during all levels of avalanche danger. Contact local authorities in your area of interest for further information.
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.