11/14- Debris from a D3 natural avalanche at snow slide gulch ended 100 vertical feet above the Lowe river.
Large avalanches (D2-2.5)also occurred in multiple other locations including Berlin Wall, Catchers Mitt, South Three Pigs and Billy Mitchell. The activity extends beyond this list, and mostly occurred during the peak of warming and precipitation on 11/13.
Multiple natural D1-1.5 avalanches were observed on multiple aspects at low elevation. No step downs noted.
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Click on link below for Thompson Pass weather history graph:
Our snow season began with above average precipitation and temperatures. Beginning in September, snow lines generally hung around 4500′ until 10/12. At that point our area received the first snow down to sea level with 12-16 inches on the north side of Thompson Pass.
On 10/15 wet conditions continued with the freezing line rising to 5000′ or higher. As skies finally cleared on 10/22 we were left with a thin rain saturated snowpack capped by a stout rain crust up to 4500′. Above 4500′ much deeper snowpacks existed due to significant early season snowfall at upper elevations.
Dry and cold conditions along with moderate outflow winds finished out the month of October.
On 11/1 precipitation returned with 18 inches of snow and ~1″ of SWE on Thompson Pass. This new snow was initially reactive with several natural D2 avalanches reported on Thompson Pass. These slides were running on a firm bed surface consisting of old rain crusts and old wind slabs from October.
On 11/4 a strong north wind event kicked up with 65 mph+ winds on Thompson Pass. Our snowpack received significant damage as already thin snow below 4500′ was stripped down to old wind slabs, rain crusts and the ground.
Precipitation returned on 11/8 and became heavy on 11/11. Storm totals of around 50 inches were recorded at Thompson Pass DOT between 11/8-11/13. Snow lines rose to ~3000′ near the tail end of the storm with heavy rain occurring in low lying areas.
Skies cleared on 11/14 through 11/18 with a strong temperature inversion setting up. Valley temperatures north of Thompson Pass fell to 0° F with above freezing temperatures existing above 4000 feet. Valdez temps remained mild. This weather allowed for widespread surface hoar up to 1 cm to develop in low lying areas.
Precipitation returned on 11/19, with incremental snowfall on Thompson Pass and areas north. The Valdez area received rain during this period. 12 inches have been recorded at TP DOT between 11/9-11/23.
11/23 Preseason update
During the 11/14-11/18 period, clear weather along with a strong temperature inversion formed surface hoar up to 1 cm in low lying areas. This surface hoar was deposited on top of the 11/13 rain crust and will be a layer of concern moving forward in specific locations.
Light to moderate snow has been falling between 11/19-11/23 on Thompson Pass with Valdez receiving rain. 12 inches of snow have accumulated on Thompson Pass in a five day period. This has slowly built storm slabs that could be reactive to human triggers.
It will be important moving forward to identify where this surface hoar is buried by the new snow and remains preserved. Elevations between 1000-3500 feet will be the most suspect especially north of Thompson Pass. Higher elevations will pose less of a threat with this avalanche problem, as warm temperatures during the inversion did not allow significant surface hoar growth. Although, shaded aspects should still be investigated.
North winds are forecasted to increase the night of 11/23 which will create a new avalanche problem, wind slabs. Wind slabs will be initially reactive on lee slopes, and have the possibility of becoming persistent where they overly the 11/19 buried surface hoar layer.
Happy Thanksgiving, and remember that it is still very early in the season. A thin early season snowpack will be unable to accept the changes that a deep mature snowpack can handle.
Click the (Full forecast +) button below for additional information. Consistent avalanche forecasts will begin December 1st.
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