Wednesday January 23, 2019
Cornice Fall, Loose Wet, Storm Slab
Travel & Terrain Advice
Prepare for inversions as you rise in elevation for the foreseeable future. Recent new surface snow will become less stable as freezing levels rise and changes in conditions with elevation become more apparent. Small loose wet avalanches combined with terrain traps may have large consequences. Avoid weakening cornices.
No new observations or reports since Monday.
Large solar input during an inversion period will cause the weakening of large fragile cornices. These cornice failures are possible especially on NW through NE aspects in the alpine and upper treeline elevations. Cornice pieces have the potential to trigger slab avalanches on slopes below them. These avalanches could be large in size (2).
If freezing levels spike as predicted, loose wet avalanches will almost certainly be widespread especially in lower elevations on solar aspects. These avalanches are likely to be small in size (1).
Early in the forecast period, reactive storm slabs will likely have formed on all aspects and elevations. These avalanches have the potential to be large in size (1-2). Expect greater hazard with increases in elevation and in wind loaded areas.
10-30 cm of snow on Tuesday fell on weak feathery surface hoar crystals on most aspects at all elevations. This potential weak layer of crystals was found on top of 30-60 cm of dry cold old storm snow which was bonding well to an old melt freeze crust which is showing obvious signs of deterioration. The snow pack below this crust is well settled and dense.
|Surface||10-30 cm low density new snow with a temperature interface down 5-10 cm.|
|Upper||Buried surface hoar to 6 mm down anywhere from 10-50 cm atop loose dry storm snow.|
|Mid||Deteriorating old melt freeze crust down 50-90 cm.|
|Lower||Well settled and dense.|
Clear calm conditions produced surface hoar development on most aspects at all elevations recently. Tuesday saw the day start with freezing fog at lower elevations turn to moderate snowfall to elevations all the way down to 700 m with accumulations of 15-30 cm. Freezing levels did not spike as previous models suggested, preserving cold dry storm snow at all elevations above 1000 m.
WEDNESDAY - No accumulation, freezing levels around 1000 m. Winds moderate to light from the NW.
THURSDAY - No accumulation with freezing levels around 900 m. Winds light to moderate from the W.
FRIDAY - Trace amounts of precipitation with freezing levels to 2800 m! Winds moderate from the NW.
Posted on Wednesday January 23, 2019 by Dan Goodwin