Eastern Sierra Avalanche Forecast - 1/17/14

Avalanche Advisory published on January 17, 2014 @ 7:00 am
Issued by Sue Burak - Inyo National Forest

We will begin issuing avalanche advisories and danger when there is enough snow. For an updated snowpack discussion, please read the discussion section. 

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advisory discussion

On cold shaded north aspects, cold nights, clear days and shallow snowpack drive the facet factory. Depth hoar grains are increasing in size and last week’s faceted particles have evolved into solid crystals with sharp edges and corners as well as glassy, smooth faces.  Strength for depth hoar and solid faceted particles decreases with increasing growth rate and grain size.  

Thin crusts enhance the greenhouse effect in the underlying snow; additional water vapor condenses below the crusts. 

ECT and PST results showed no propagation using the ECT standard length beams (90-100 cm).  The PST is a snowpack test that indicates the propensity of a pre identified slab and weak layer combination to propagate a fracture. PST's resulted in mixed results- fractures propagated to the end of the column or arrested within the layer in the same snowpit. It will be interesting to see if ECT and PST test results change in this area over the course of a week. The variability of the results are difficult to interpret until we revisit the area next week. 


recent observations

Many ECT and PST tests wre done yesterday. Despite large weak depth hoar and a snowpack composed of alternating suncrusts and solid facets, ECT's did not propagate in any of the buried weak layers. The PST results at 35 cm down in a 60 cm snowpit suggested propagation was likely.  Thin, soft large grained weak layers with no differences in hand hardness were specific snowpack characteristics that were not conducive to propagation. Slab fractures (SF) were common in the ECT tests. 

weather summary

Dry and mild conditions continue for the week. Nights will be cold in low lying areas. Low temperatures in higher elevation locations such as Mammoth Pass are relatively warm, dropping only to the upper 20’s compared to the low 20’s at mid slope locations such as Mammoth Lakes.

Weatherwest.com  has a thorough discussion on "the Ridiculously Resilient Ridge remains resolutely recalcitrant."  The same ridge was present last year  (2012-2013) and is still entrenched over the western U.S.  

With a huge ridge over the western U.S. the dry spell is expected to continue for at least the next week.  Seasonal predictions are more uncertain than weather prediction, and the pattern can shift quickly and bring a lot of snow in a short period of time, but there is such a large snowpack deficit, it would take many,  many multi day storms to bring the snowpack  back  to near average.

An interesting aspect of jet stream behavior is that when the western U.S. is under a ridge, the eastern U.S. is usually under a trough (and vice versa).  This is because the typical distance between long-wave ridges and troughs at jet stream level is about the distance across the contiguous U.S. 

Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 29 deg. F.
Max. temperature in the last 24 hours: 47 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 5-10 mph
Maximum wind gust in the last 24 hours: 10 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 14 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Friday Friday Night Saturday
Weather: sun clear sun
Temperatures: 46 deg. F. 31 deg. F. 46 deg. F.
Mid Slope Winds: S N NE
Expected snowfall: 0 in. 0 in. 0 in.
Over 10,000 ft.
Friday Friday Night Saturday
Weather: sun clear sun
Temperatures: 46 deg. F. 23 deg. F. 46 deg. F.
Ridge Top Winds: Sw N E
Expected snowfall: 0 in. 0 in. 0 in.
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