Turnagain Pass

A series of small low-pressure systems are circulating through the Gulf and into Prince William Sound bringing snow showers to our region. Overnight 3-6” fell between Turnagain Pass and Girdwood and another 6-12” is possible today. Its also possible that parts of our forecast zone may only see a few more inches. Unfortunately these types of weak systems make for a challenging snow forecast. Yet, as we saw last week, a system such as this one turned out to produce feet of snow in the Placer Valley. This may be the case again today and the avalanche danger will depend on how much snow falls and how much the winds build today. UPDATED: As of 7am ridgetop winds have increased into the 15-25mph range and are expected to remain elevated through mid day.

Snow surface prior to this storm consisted of surface hoar with loose faceted snow underneath on shaded aspects, and a sun crust on solar aspects (SW – SE). Both of these surfaces will be hard for any decent amount of new snow to stick to. Storm related wind slabs and loose snow avalanches will be the most likely avalanche problems and are expected to be easy to initiate. 

STORM/WIND SLABS: Today’s new snow and ridge top winds 15-25mph could form slabs 1-2′ thick. The size of these will depend on the total amount of snow and how much the wind blows. Remember that larger terrain features could produce larger slabs and if winds stay elevated above 15mph slabs could be more conected than expected. Keep slope angles below 35 degrees and avoid terrain traps like being at the bottom of gully.

DRY LOOSE SNOW AVALANCHES (SLUFFS): Today’s snow is expected to be very loose and unconsolidated making to really easy to trigger dry loose snow avalanches on steeper terrain features protected from any wind.  Expect sluff to be fast moving and if snow totals are closer to 12” they could easily be larger and run further than expected. 

WET LOOSE AVALANCHES:  If for some reason the sun pokes out and begins to warm the snow surface to the point of melting, it will be important to watch for wet loose avalanche activity on Southerly slopes. Avoiding these areas at times of melting is recommended.

Old surfaces vary depending on aspect and elevation. On Southerly slopes a sun crust is present and in some places this crust has near surface facets on top as was the case on Lips South face yesterday.

Surface hoar ranging from small (4-6mm) to very large (1-2cm) has been well documented at all elevations on W – N – E aspects. Poor bonding is expected on these surfaces.

Yesterday a skier triggering a small slab avalanche on a steep Northern chute on Orca, near Girdwood. The avalanche was actually triggered by their fast moving sluff below them, as they were stopped, letting the loose snow pass by. The slab was small, 12” deep and 20’ wide, but ran the full length of the avalanche path. This is a good reminder that some slopes harboring old slabs 1-2′ thick are sitting on weak faceted snow. These slabs are composed of last week’s storm snow and have mostly been eaten away with the cold temperatures – faceting to the point they are now a weak layer themselves. Yet, there are places where the slab is more consolidated, thus another reason to avoid steep slopes today if we see heavy snowfall.

Skier triggered slab on Northern chute of Orca, near Girdwood, yesterday. No one was caught in this avalanche.