Avalanche Advisory: Thursday - Feb 21, 2019

THIS AVALANCHE ADVISORY EXPIRED ON February 22, 2019 @ 6:36 am
Avalanche Advisory published on February 21, 2019 @ 6:36 am
Issued by Josh Feinberg - Eastern Sierra Avalanche Center

MODERATE avalanche danger in the form of WIND SLABS exists at upper and mid elevations on all aspects due to shifting winds transporting old and new loose snow.  Human triggered wind slab avalanches are possible in exposed areas. LOOSE DRY sloughs are also a concern in lower elevation steep sheltered terrain.

2. Moderate

?

Above Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

?

Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

1. Low

?

Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Winds have been shifting back and forth on the daily from southerly to northerly.  Today they are back out of the north at moderate speeds.  With old loose snow still being transported, and an additional few of inches of new low density snow from yesterday and last night (and an inch or two possible today) isolated wind slabs sensitive to human triggering are likely to be found at mid to upper elevations on any aspect.  Let the avalanche that occurred on Tuesday in extreme terrain be a reminder that just because conditions are seemingly stable in most areas, doesn’t mean they are everywhere.  Wind slabs today could range from smooth and sensitive to etched, rough and stubborn.  These are likely to be found just below ridgelines, the sidewalls of gullies, and around mid-slope terrain fluctuations.  Watch for signs such as shooting cracks as indications that wind slabs are sensitive.  While likely to be relatively small, these wind slab avalanches could knock a person off their feet and lead to a nasty fall in consequential terrain and even a burial if a terrain trap is involved.

Also be cautious on ridge tops where large CORNICES may be found overhanging easterly to northerly facing slopes.  Stay well back from the edge if there is any uncertainty!  

Avalanche Problem 2: Loose Dry
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Cold temperatures have kept snow soft and loose in more sheltered terrain. Reports continue of sizeable loose sloughs in steep lower elevation terrain, where shallowly buried icy rain crusts exist with soft snow on top. These sloughs could be large enough to knock someone off their feet and leave an icy bulletproof slope behind. A burial can even be possible if a terrain trap is involved. Manage slough wisely, or avoid steep sheltered terrain.

advisory discussion

Rain over Valentine’s day led to firm icy crusts up to around 10,000’+, which were then covered by additional snowfall. In wind swept areas and at lower elevations where these icy crusts are at the surface or only shallowly buried, slide for life conditions exist!  Surprisingly large expanses of sheen could be seen throughout exposed areas in the Sherwins yesterday where this rain crust is reflecting sun.  A fall would be very difficult to arrest even on low angled slopes with this crust!

In terms of avalanches, this ice crust is a smooth bed surface for looser snow to easily slide on. Ice crusts are also notorious for developing weak faceted snow just above and below them.  Especially with the cold temperatures we have been having, we will be monitoring these layers closely.  Please submit your observations of these layers, and any other observations you may have to our site as well!    

Weather and CURRENT CONDITIONS
weather summary

Mostly cloudy skies with scattered snow showers are expected today with an inch or two of new low-density snow possible.  Moderate northerly winds are forecasted with gusts into the mid 40s at upper elevations where high temperatures should reach only into the single digits. North winds will continue thru tonight with another inch of snow possible in some locations.  

Tomorrow will be slightly warmer with continued north winds, and sunshine likely in the afternoon.

Two-Day Mountain Weather Forecast Produced in partnership with the Reno NWS
For 8,000 ft. to 10,000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy. Scattered snow showers. Snow levels below 7000 feet. Chance of precipitation is 55%. Mostly cloudy. Scattered snow showers. Snow levels below 7000 feet. Chance of precipitation is 40%. Partly cloudy then becoming sunny.
Temperatures: 13 to 21. deg. F. 1 below to 5 above zero. deg. F. 21 to 29. deg. F.
Mid Slope Winds: North 15 to 25 mph with gusts to 35 mph. North 15 to 25 mph. Gusts up to 40 mph decreasing to 30 mph after midnight. North around 15 mph with gusts to 25 mph in the morning becoming light.
Expected snowfall: 80% probability up to 2 inches. 20% probability of 2 to 4 inches. | SWE = up to 0.15 inch. in. Up to 1 inch. | SWE = less than 0.10 inch. in. 0 in.
Over 10,000 ft.
Thursday Thursday Night Friday
Weather: Mostly cloudy. Scattered snow showers. Snow levels below 7000 feet. Chance of precipitation is 55%. Mostly cloudy. Scattered snow showers. Snow levels below 7000 feet. Chance of precipitation is 40%. Partly cloudy then becoming sunny.
Temperatures: 4 to 9. deg. F. 5 below to zero. deg. F. 12 to 17. deg. F.
Ridge Top Winds: North 15 to 30 mph with gusts to 45 mph. North 15 to 30 mph. Gusts up to 55 mph decreasing to 45 mph after midnight. North 15 to 25 mph. Gusts up to 35 mph.
Expected snowfall: 80% probability up to 2 inches. 20% probability of 2 to 3 inches. | SWE = up to 0.15 inch. in. Up to 1 inch. | SWE = less than 0.10 inch. in. 0 in.
Disclaimer
This Avalanche Advisory is designed to generally describe avalanche conditions where local variations always occur. This product only applies to backcountry areas located outside established ski area boundaries. The information in this Avalanche Advisory is provided by the Eastern Sierra Avalanche Center, who is solely responsible for its content.

ESAC receives support from ...