Friday April 6, 2018
Wind Slab, Deep Persistent Slab, Loose Wet
Travel & Terrain Advice
Avoid areas with freshly wind loaded snow and cross loaded features.
Avoid travelling near or below cornices.
Avoid avalanche terrain when rain on snow events occur and temperatures warm rapidly.
Choose low angle terrain, simple or non avalanche terrain and be very cautious of even the slightest exposure to overhead hazards
Avalanche control teams at Mount Washington report ski cutting triggering numerous wind-slab avalanches on western aspects and found on all aspects new snow instabilities touchy to skier traffic. These avalanches were size one and easily triggered with light loads and on specific terrain features widespread propagation was noted. Numerous explosives testing produced size 1.5 avalanches on north westerly terrain and had crowns down 20 to 30 cm. One explosive test on a south west aspect produced a large slab avalanche down between 60 and 80 cm and was large, size 2 and it ran far and fast.
During the early PM on Thursday temperatures and freezing levels continued to rise with precipitation falling as rain to treeline. Numerous small loose wet avalanches were reported on all aspects and at all elevation from treeline and below. Signs of instability such as pinwheels from steep thin areas where reported as widespread and especially prevalent on steep slopes with rocky out crops and thin areas.
Expect these conditions to persist through this forecasting period, as freezing levels will remain high, snowfall that does occur will be moist and heavy and in westerly regions of the forecast area, precipitation amounts may exceed 50 mm in volume.
Strong south east wind and moderate snow fall has deposited up to 80 cm of new snow on lee aspects. These hazardous avalanche problems are located predominately in the alpine and treeline on all western aspects. Expect these avalanche to be touchy to very touchy to human triggering and if triggered will propagate far and wide and produce large to very large avalanches.
Deep Persistent Slab
A robust melt freeze crust buried March 22 and found on all aspect and elevations is stubborn to triggering and becoming dormant. These hazardous avalanches if triggered will produce very large avalanches.
Past rain and forecast rain unconsolidated the upper snow pack making it very touchy to human triggering. Found on all aspect and elevations, if trigger will start as a small avalanche but will gain mass and may have enough power to push a mountain traveller into or over terrain traps.
Moderate to strong south east wind and moderate to heavy snowfall have in areas lee to this wind buried a melt freeze crust down between 40 and 60 cm. This new snow fall has become moist and is bonding poorly to the old surface. Below the well establish melt freeze crust, another crust initially buried March 22 is now down between 100 cm and 130 cm. Numerous Testing of the March 22 crust produced no results, the crust however is well defined and may wake up with a big enough load. The mid and lower snow pack are well settled and dense.
|Surface||variable surface conditions, some areas scoured to old crust other in the lee of the wind, up to 60 cm of moist new snow all sitting on a melt freeze crust|
|Upper||new moist snow|
|Mid||widespread March 22 melt freeze crust and in isolated protected north aspects areas its suspected that surface hoar and surface facets may have been buried on this crust|
A period of cold temperatures has been followed by a warm front bringing rising temperatures and freezing levels with moderate to strong south east winds.
A low pressure located to the north west of the region, will bring to the forecast area rising freezing levels, warming temperatures, and moderate precipitation amounts. Rainfall is expected to breach the 1800 meter mark Saturday and any snowfall above this elevation will be heavy moist and perhasp wet with potential to trigger large natural avalanches
Friday 10 mm of rainfall. Temperatures 2 overnight rising to 4.5 mid day, winds light to moderate south east . Freezing level rising to 1700 m mid day.
Saturday 50 mm of rainfall. Temperatures 4 overnight rising to 5 mid day, winds moderate east south east. Freezing level rising to 1900 m mid day.
Sunday 5 mm of rainfall temperatures 3 rising to 6 mid day, winds light to moderate south west. Freezing level rising to 1700 m mid day.
Posted on Friday April 6, 2018 by Jesse Percival