Mammoth Basin Snowpack Summary - 2015-02-20 07:00

Avalanche Advisory published on February 20, 2015 @ 7:00 am
Issued by Sue Burak - Inyo National Forest
Avalanche Character 1: Normal Caution
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Use normal caution when travelling in the backcountry.
Snowpack Discussion

Ridiculously warm February temperatures and longer days had their way with the snowpack the last week.  Snow melted off south and west slope at mid elevations and mid elevation north facing slopes not protected by rock cliffs also had enough sun to create thin crusts. On the other hand, high elevation shaded north slopes are still cold and will remain cold for another month. The best skiing conditions have been in high elevation terrain in the Negatives and Virginia Lakes.

In general, the snowpack is the same at mid and high elevations- a few inches of dry snow over a thick supportable wind/rain/dense snow layer that formed the first weekend in February. Dry snow is limited in the high elevations of the Mammoth Basin though there is plenty of wind effected snow and minor sastrugi above treeline. Dry snow in shaded north and east facing gullies remain in the Negatives and Virginia Lakes area.

Underneath skiable snow and firm supportable layers are dry rounds and facets sandwiched between the surface and the old January surface. Reports and observations from Mammoth Basin, the Negatives and Virginia Lakes reveal a similar base layer- weak and faceted with some depth hoar- the remnants of the snowpack of December and January.  

As both daytime and night time temperatures fall this weekend, expect the faceting process to accelerate and continue to weaken the two prominent crust layers in this dreadfully dry winter.


recent observations

Observations made yesterday from 9,000 to 10,000 ft. in the Mammoth Lakes Basin matched up with recent observations from the June Mtn area. Snowpit data from north aspects located at around the 9,800 ft. elevation in the Mammoth Basin showed a knife hard surface layer with areas of near surface facets where the wind had transported snow into depression and sheltered areas. Under the layer was 10 cm of rounded bonded clusters. The old layer from January was deteriorating from below the crust as facets and clusters of faceted grains continue to grow in size and cannibalize the crust. The old snowpack from December and January was fist hardness facets and depth hoar.

Observations of similar snow structure were made and reported from the Negatives and Virginia Lakes areas. Thin crusts formed during alternating warm and cold spells in January are no longer seen in snowpits because faceting transformed crusts into disaggregated square particles. This snow struture is found on all aspects though at lower elevations, the snow is moist.

On south and east facing slopes above 9,000 ft in the Mammoth Basin, a medium thickness layer of spring snow exists in open areas- forested slopes have a variety of icy to uneven surfaces shown in the lower photo.

An example of hideous snow surfaces in the trees at 9,000 to 9,400 ft.


CURRENT CONDITIONS Weather Observations Between June (10,000 ft.) and Mammoth (11,000 ft.)
0600 temperature: 28 deg. F.
Max. temperature in the last 24 hours: 38 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 15 mph
Maximum wind gust in the last 24 hours: 28 mph
New snowfall in the last 24 hours: 0 inches
Total snow depth: 21 inches

A cooling temperature trend begins today and will continue into the weekend. By Sunday, it will be COLD, with temperatures 5 to 10 degrees below normal for this time of year. Northerly winds will bring wind chill temperatures down to the teens. Snow showers are expected Sunday but accumulations will be light.

For today at the 9,000 ft. elevation, skies will be clear with highs in the upper 40’s- Saturday’s highs could reach 40 F but the big chill arrives Sunday when the high is projected to reach 27 F. High elevations will in in the mid 40’s today, mid 30’s on Saturday and around 20F on Sunday. This is a 30 degree drop in temperatures from what we have become accustomed to.  Nights will reach the teens by Saturday night.

All eyes are glued to each consecutive 12 hour model output run, hoping a significant pattern change will occur next weekend.

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: clear, sun clear winds
Temperatures: 48 deg. F. 32 deg. F. 42 deg. F.
Wind direction: NW NW N
Wind speed: 10-15 15-40 30-50
Expected snowfall: 0 in. 0 in. 1-2' in.
Over 10,000 ft.
  Friday Friday Night Saturday
Weather: clear clear partly cloudy
Temperatures: 38 deg. F. 25 deg. F. 32 deg. F.
Wind direction: NW NW N
Wind speed: 20-30 30-40 50-60
Expected snowfall: 0 in. 0 in. t in.

This snowpack summary applies only to backcountry areas outside established ski area boundaries. This snowpack summary only describes general avalanche conditions and local variations always occur. This snowpack summary expires 24 hours after the posted time unless otherwise noted. The information in this snowpack summary is provided by the USDA Forest Service who is solely responsible for its content.

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