Avalanche Forecast

A weak disturbance is expected to bring clouds and light snowfall across the forecast area overnight Thursday and Friday. Only light amounts of new snow are expected and should not cause an increase in danger. Moderate NW winds at higher elevations may continue to transport available snow, building areas of wind slab on a variety of a-typical aspects from east to southwest facing. 

While the overall danger should continue to decrease, continue to travel with caution and watch for any slab like structure or cohesion in the upper snowpack, indicating the possibility of slab avalanches propagating.

Watch for touchy recently formed cornices and avoid travel on steep unsupported slopes.

Recent deep storm snow has been settling and stabilizing Wednesday and Thursday under fair cool weather. This has allowed for storm related weak layers to settle with no storm slab avalanches reported since Tuesday.

Moderate to strong northerly crest level winds have been transporting snow on many exposed ridges both Wednesday and Thursday. This should have built areas of wind slab on a variety of aspects, including non-typical southerly facing slopes near and above treeline.

Numerous field obs Wednesday and Thursday indicate the previous very sensitive storm layers have settled and continue to stabilize. Cooling temperatures and light winds have left a favorable storm snow profile of increasing density with depth and some fabulous skiing and riding conditions. 

The old snow interface formed during the high pressure in early December and buried 12/15 appears to be favorable as well, from observations received Wednesday and Thursday.

The main take away is the current upper snowpack in most areas near and below treeline, away from ridges and wind transport, remains of low cohesion and lacks the structure to support slab avalanches. Wind and warming and just some surface settlement can change that structure however, so continue to watch for changing surface snow conditions. 

There was a freezing rain crust that formed Monday above 6000 feet at Mt Hood Meadows which should be noted, see image below. 

Winds above treeline have shifted and strengthened from the N-NW Wednesday, transporting the abundant new snow forming wind stiffened snow or wind slab on a variety of aspects, especially near and above treeline.  

The snowpack near and above treeline may be very different as there are likely wind slabs lurking. Limited observations above treeline means a lower confidence and hence travelers should approach with a high margin of safety. 

The total storm snow Monday through early Wednesday ranged from 2-4 feet over the Mt Hood area.

There's plenty of great snow at mid and lower elevations, so eliminating any potential wind loaded terrain may be the best plan. 

Observations

The first explosive control since the recent storms occurred Thursday above treeline at Mt Hood Meadows, producing limited slab avalanches with a few size 1 slabs releasing on terrain that had wind effected surface snow. 

The Meadows pro patrol on Wednesday reported less avalanche activity than Tuesday, however wind slabs continued to be released with explosives and active wind transport was occurring Wednesday near and above treeline with strong NW winds.

The Meadows pro patrol on Tuesday reported new wind slab forming near tree line and did not need to venture to the above tree line. New snow was bonding well to previous surface below tree line.

NWAC pro oberserver Laura Green was in the Heather/Mitchell drainages on Tuesday in low visibility conditions, her test results indicated several storm layers in about 1 foot of new snow but with low quality results. Total snow depths were quite varied and the new snow was bonding well to previous melt freeze snow.

On Monday the Meadows pro patrol reported a major freezing rain event with up to 6-8 inches of ice in the 6000-7300 foot elevation range, with rain softened snow at lower elevations.

Ice coated tree limbs at Mt Hood Meadows on Monday December 18th. Photo Nick Burks.