Northwest Avalanche Center NWAC, Northwest Avalanche Center

Cascades - North East Avalanche Forecast

May 15th, 2017 9:55AM

A mix of winter-like avalanche problems is expected on Tuesday. Backcountry travel is not recommended in the above and near treeline in the southwest zone and especially at Mt Hood on Tuesday. Careful snowpack evaluation and cautious routefinding will be essential in other areas.

Summary

Detailed Forecast

See above.

Snowpack Discussion

Like a Santa that keeps coming back to town this is the winter that keeps on giving! Just make sure you are paying attention to conditions and forecasts so it doesn't turn around and bite you.

A significant late season front will cross the Northwest on Monday night. An upper low pressure system and cold, unstable air mass will follow and move across Washington on Tuesday.

Weather:

On Monday night look for increasing moderate southwest alpine winds and increasing moderate to heavy rain or snow near and west of the crest with lowering snow levels.

On Tuesday we should see a change in the north to light west alpine winds and light snow, in the central moderate west alpine winds and light to moderate snow, in the south moderate to strong west alpine winds and moderate to heavy snow, and at Mt Hood strong west alpine winds and heavy snow. The air mass will be unstable enough for a chance of thunderstorms along the Cascade west slopes and Mt Hood. Snow levels will continue a downward trend to about 3500 feet in most areas by Tuesday late morning with a little bump possible due to May solar effects Tuesday afternoon.

How about some back of the envelope estimates for new snow for the Monday night through Tuesday afternoon period: Mt Baker about 4-6 inches, Stevens and Snoqualmie Passes (above the passes) 6-8 inches, Paradise 8-12 inches, Mt Hood 10-20 inches. Less new snow is likely east of the crest.

Avalanches:

The weather Monday night and Tuesday is likely to cause a return of a mix of winter-like avalanche problems such as wind slab, storm slab and loose dry conditions in the above or near treeline Tuesday. Loose wet avalanches should also be possible Tuesday due to new snow and strong spring sun effects on solar slopes. Sun effects can help activate even shallow new snow and previous firm snow can provide good smooth bed surfaces - this includes ski runs at closed ski areas.

Backcountry travel is not recommended in the above and near treeline in the southwest zone and especially at Mt Hood on Tuesday where new snowfall should be heaviest. Careful snowpack evaluation and cautious routefinding will be essential in other areas. Less snow and less danger is likely along the east slopes of the Washington Cascades.

Due to stronger winds and heavier snow, conditions are likely to be more severe above the crest level on the south volcanoes such as Mt Rainier, Mt St Helens, Mt Adams and Mt Hood.

Outlook:

A transition day is likely on Wednesday. A general trend of warmer drier weather should finally be seen starting Thursday and potentially lasting through next week. More special statements for spring avalanche conditions seem likely later this week.

Valid until: May 16th, 2017 9:55AM