Lawinenlagebericht

Purcells

Feb 29 – Mar 1, 2020Avalanche Canada
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Lawinengefahr

Mon
Tue
Hochgebirge
3 · Erheblich
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

If snowfall amounts exceed 15cm be alert for signs of instability, especially in wind affected terrain or where slab properties are building on buried surface hoar instability. Remain cautious around shallow snowpack areas, particularly if threatened by cornices. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible - Likely
    Größe
    1–2

    New snow with be easily transported by moderate to strong winds overnight building fresh windslabs where precipitation reaches 10cm. These windslabs will lie on buried windslabs, meltfreeze crusts or buried surface hoar. Fresh snow will be touchiest where wind affected.  

    A widespread persistent surface hoar layer may become reactive once enough snow accumulates and forms slab properties. The western half of the region may be reaching a threshold amount of snow to be able to trigger the surface hoar and Friday's warming trend could help build slab properties across the region.

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely - Possible
    Größe
    2–3.5

    Weak snow at the bottom of the snowpack continues to pose a deep persistent slab avalanche problem. Treat wind scoured, rocky, shallow terrain as suspect. Also avoid big alpine slopes that are threatened by cornices overhead. 

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

FRIDAY NIGHT: Cloudy with scattered flurries, accumulation 5 to 10 cm. Winds moderate to strong southwest. Alpine low temperatures around -9 with freezing levels dropping to 800m with cold front passage.  

SATURDAY: Cloudy with scattered flurries, accumulation Trace to 5 cm. Winds moderate West gusting strong. Alpine temperature -7 C with freezing levels 1100 m.

SUNDAY: A mix of sun and cloud. Winds light Westerly. Alpine high temperatures near -8 C and lows of -12 C.

MONDAY: Cloudy with sunny periods and isolated flurries. Winds moderate West gusting strong. Alpine temperatures high of -5 and lows -10 C with freezing levels near 1000m

Avalanche Summary

A few small (size 1 to 1.5) wind and storm slab avalanches were triggered by humans each day Monday thru Wednesday with activity tapering on Thursday. They occurred on all aspects, were from 2100 to 2700m and were 15 to 40cm thick. In the Western (& deeper) portion of the region a few of the avalanches released on the surface hoar layer described in the Snowpack Summary.

Snowpack Summary

New snow and moderate strong winds are forecast to arrive Friday night into Saturday with a fast moving cold front. Total precipitations will vary from 5 to 20cm, with more snow forecast in the North and in the higher mountains of the West of the forecast region.. 

This new snow will build on the previous 10 to 30 cm of recent snow which covers a widespread layer of surface hoar (size 5 to 15 mm) that was found at all elevations and on all aspects. Recent warm temperatures have built slab like properties in this recent snow, particularly at mid and low elevations. The recent snow has been blown around by variable wind, forming wind slabs at higher elevations, particularly near ridges.  

The middle of the snowpack is strong. The base of the snowpack contains basal facets, which have been responsible for occasional and hard-to-predict Deep Persistent Slab avalanches in shallow rocky start zones.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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