Avalanche Forecast

Quite a change is in store on Monday.

A strong cold front will cross the Northwest on Monday. This will cause strong west crest level winds, moderate to heavy rain changing to snow heaviest near and west of the crest, and cooling and lowering snow levels. These conditions should generally spread from the Olympics and north Cascades Monday early morning to the south Cascades Monday late morning to Mt Hood by Monday afternoon.

During the day on Monday this weather should build some new wind slab in the alpine and some shallower wind slab in near treeline areas on lee slopes. Remember that it can be difficult to determine where wind slab lies but it often has a chalky texture and may be triggered from thin areas near the edge of the slab. Storm slab seems more likely in mostly calmer below treeline areas especially where snowfall rates exceed about an inch per hour.

A high danger is not in the forecast mainly due to the expected cooling trend. But a considerable danger still means dangerous avalanche conditions.

In areas with light wind, where rain changes to snow, and with lower rates of loading, the cooling trend should help bond new snow to old snow and help build right side up conditions with lower density snow nearer the surface. This can mean some good skiing in those types of areas. Underlying wet snow should also begin to refreeze and strengthen.

Shallow snow cover and shallow new snow will continue to limit the avalanche danger at lower elevations.

Remember this is a regional forecast and you must make your own on site evaluations to see if they are different than forecast.

Warm wet weather the weekend of 14 and 15 December created another crust layer in most areas. This seems to have capped and stabilized underlying hoar frost and faceted snow and made those layers generally unreactive.

Cold weather, light amounts of low density snow and some surface hoar formation were generally seen mid-week last  week.

This set the stage for warmer wet weather that was seen Friday and over the weekend. A warm front moved across the Northwest Friday. This generally caused strong southwest winds, increasing moderate to heavy snow and greatly warming temperatures. Another warm front moved across the Northwest on Saturday night and Sunday. This generally caused strong northwest winds and wet snow or rain at further warming temperatures. NWAC sites near and west of the crest for the 48 hours ending Sunday morning had ended up mostly with about 4-17 inches of very wet heavy snow. The warming should have created some unstable upside down wind or storm slab conditions at alpine elevations and wet loose conditions near or below treeline.

Reports are a bit sparse for the weekend probably primarily due to the poor ski conditions. A couple of most pertinent observations follow. The Hurricane ranger reported shallow consolidated snow, little new snow and a lower danger in that area on Saturday and Sunday. The Mt Baker ski patrol reported fairly extensive ski triggered wind slabs Friday and Saturday. An NWAC observer just east of Stevens Pass on Saturday reported that the recent snow gave some cracking and small wet loose avalanches. The Mt Hood Meadows ski patrol Saturday and Sunday reports a stable freezing rain crust in the alpine and near tree line but it is unknown if this condition extends very far around the mountain.

Shallow snow cover has been limiting the avalanche danger at the lowest elevations.