Friday February 5, 2021
Persistent Slab, Loose Dry
Travel & Terrain Advice
Be cautious when route-finding and transitioning from scoured areas into areas of wind loaded snow.
Avoid travelling above or below cornices especially during the period of warming.
Confidence details: Numerous submissions and in field observations and terrain travel provide a good base line for this forecast. Some of the weather models are in conflict and this centers around the freezing levels and timing of the artic cooling period.
This weeks extensive explosive avalanche control and testing at Mount Washington was mostly on cornice features and lee aspects affecting north aspects between 1500 and 1600 meters. These large triggers impacted steep terrain and did not “wake” up the surface hoar instability.
This problem has now become stubborn to triggering and will likely become unreactive near the end of the forecast period.
Location: Specific to Alpine areas as warming and rapid settlement at lower elevations has helped to bond this instability.
Possibility: Triggering of this avalanche problem from light loads such as skiers are unlikely to possible. Natural avalanches are unlikely.
Size: If triggered, expect these avalanches to be large size 2 and will be big enough to bury, injure or kill a mountain traveler.
This problem may be small but in isolated steep terrain should be considered.
Location: Specific to Alpine areas where loose and dry unconsolidated snow exists.
Possibility: Triggering of this avalanche problem from light loads such as skiers is possible to likely. Natural avalanches are unlikely.
Size: If triggered, expect these avalanches to be small size 1 but could gain mass and push a traveler into a terrain trap.
Snowpack is settling with numerous layers within the upper and mid snowpack. Testing Thursday indicated there is a shear down 75 to 100 cm and this is a surface hoar layer that was buried January 22. The layer is present but no settlement or cracking was felt during travel in unmodified and undisturbed snow. The testing performed did not present as overly concerning, however this layer may be problematic in isolated areas at elevations above 1800 meters.
|Surface||Moist and dense.|
|Upper||Settled and dense broken precipitation particles.|
|Mid||decomposing surface hoar layer down 75 to 100 cm.|
A warming trend and some sun has allowed the snowpack to settle out and become warm.
The current northwesterly flow will continue to deliver moderate snow fall amounts and a variety of freezing levels southerly areas within the forecast zone such as 5040 may see freeing levels as high as 2000 meters with norther zones such as Mount Cain may see a rise to a little as 1100 meters. In the wake of this storm front, an artic high pressure will enter the region bring with it clear sky and cooling temperatures.
Friday: 10-15cm of snow, Winds Moderate from the Northwest, Freezing levels 2000 dropping to 1200 meters.
Saturday: 5- 10cm of snow, Winds Light to Moderate from the South West, Freezing levels 1000 meters.
Sunday: No new snow. Winds Moderate from the North West, Freezing levels near sea level.
Posted on Friday February 5, 2021 by Jesse Percival