Friday January 26, 2018

Sunday January 28, 2018
Saturday January 27, 2018
Friday January 26, 2018
Confidence: High - Forecast weather models are in agreement for the region and many days of field research.

Main Concerns

Loose Wet, Wind Slab, Loose Dry - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Friday and Saturday watch for loose dry avalanches and wind slab. Avoid steep wind loaded terrain on NE-NW aspects in the alpine, treeline and open below treeline. Steep convex features and unsupported terrain are prone to release down to the firmer snow surface approximately 10-30 cm below. Use slough management to avoid being pushed by moving loose dry snow especially if exposed to terrain traps (like cliffs, depressions, tree stands, and rocks). Sunday….. Very high potential for rain to saturate our upper snowpack right up in to the alpine. This rain will lead to widespread loose wet and possibly wet slab activity. the hazard for this period will be high for all elevations and aspects so travel in all avalanche terrain is NOT recommended.

Avalanche Summary

Tuesdays strong to extreme winds pressed surfaces and loaded NE-NW slopes. Very limited visibility hampered avalanche observations, but we expect there was natural activity during this time due to wind loading. Wednesday temp dropped and the wind hardened surface tightened up and reduced activity. New snow Wednesday night and Thursday was moving easily with natural and human triggers. Natural slab avalanches were seen on NE asp at treeline up to size 1.5. Ski cutting, by Mt Washington avalanche control teams, produced numerous Loose Dry slides up to size 1 (running far and fast), a few size 1.5 soft slabs and one size 2 soft slab. All these ski cut results were treeline and below, on N to NE aspects, were in steep terrain to unsupported convex features and were the new snow running on the old wind hardened surface.

Avalanche Problems

Loose Wet

It is almost certain that we will see WIDESPREAD loose snow avalanches with Sundays warm rain event. These avalanches will be on all aspects and at all elevation bands and will certainly be reactive to both natural and human triggers. We can expect to see them up to size 2, and when combined with exposure to terrain traps these pushy powerful soughs will be very dangerous.

Wind Slab

Convex features and steep unsupported terrain in the alpine, treeline and open below treeline may have wind slabs present. These slabs are typically on NE-NW aspects and cross-loaded features and are likely to trigger naturally and very likely to run with human loading. These avalanches have the potential to be up to size 2 on specific terrain and even size 3 in isolated terrain.

Loose Dry

Expect widespread loose dry avalanche activity Friday and Saturday on steep terrain on all aspects and elevations. These sloughs may possibly trigger in steep terrain naturally and are very likely to trigger with human activity. They have the potential to be up to size 1.5 and their consequences will be magnified by the presence of terrain traps.

Snowpack Summary

10-20 cm of new snow sit poorly bonded to a firm wind pressed surface. Very high winds last Tuesday have transported significant quantities of snow to lee slopes and have left many wind sculpted features near ridge tops (snow drifts). Generally great sliding in enjoyable fresh snow!

Snowpack Details

Surface10-20 cm of fresh with a couple thin crust like films (not noticeable while skiing) Lots of sporty wind features to play on.
UpperFirm windpressed snow (snow above bonding poorly to this).
MidThe big blizzard event (one meter plus) snow has settled down and seams to be nonreactive as cold temps have tightened it
LowerWell settled.

Past Weather

Since the very high winds Tuesday, light to moderate snow had fallen. Temperatures have dropped significantly (-7 to -9.5 at times) and winds have been relatively light from the south east to north east.

Weather Forecast

Friday - light to moderate snowfall with cold temps and light to moderate winds from the SE-SW, freezing levels 200-850 m. Should be a great day to play!

Saturday - light to moderate snowfall with cold temps and moderate to strong NE-SE winds, freezing levels 300-1000 m. Let the fun continue!!

Sunday - moderate to heavy rain, light snowfall and even the possibility of light freezing rain, warm temps near +4 and very high winds from the south, freezing levels starting out at 600 and quickly rising to 2400 m. Not so fun!!

Posted on Friday January 26, 2018 by Bill Phipps

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