Bollettino valanghe

Mt Hood

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Wind slabs will be unlikely but not impossible to trigger on Tuesday. While there was limited snow available for transport on Thursday, any snow that does fall will drift into fresh, shallow slabs you can trigger on a steep slope. Active drifting of any shallow new snow will be your best clue to increase your level of caution.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1

    Old wind slabs have mostly lost reactivity, so we're focusing on recent or fresh snow transport. If an inch or more of snow falls (slightly more than we expect), moderate winds will isolated slabs up to 6" deep in "frequent flyer locations" where you could trigger an avalanche on a slope 35 degrees or steeper. Use visual clues such as blowing snow or sharp, fresh cornices to identify and navigate away from any problem areas. Use quick hand shears to test the bond of any drifts to the underlying snow or ice interface. If the drifts shear cleanly, they could be more reactive in your area. If you find anything that doesn't line up with LOW danger, take a step back and steer around potentially problematic wind-loaded areas.

     

    Drifting snow above treeline.

    Photo: Joe Dellaporta

Avalanche Discussion

The upper snowpack is strong and strengthening with good riding conditions and minimal stability concerns.  

Joe Dellaporta was on Pea Gravel Ridge on Friday. A snow profile on a SE aspect at 5200 ft showed 35 cm of right-side-up storm snow well bonded to the crust 2/13 melt-freeze crust. This crust was 0.5" thick in this location but would be thinner on shaded aspects and at higher elevations. Below the crust, he found a layer of graupel (lower density) which was not present at Tilly Jane. The 2/3 crust was down 2 ft and the MLK crust was down almost 3 ft. He found milder-than-expected conditions on Friday, which helped reverse some weakening snow surfaces. Surface hoar was still in sheltered meadows and near streams in Heather Canyon. Mild temperatures combined with morning sunshine to break down crusts on sun-affected aspects and produced some rollerball activity on SE-S-SW-W aspects. Moist snow surfaces on most aspects receiving any sunshine on Friday will form a crust by Saturday. An isolated, shallow wet loose avalanche (pictured) ran naturally on a sun-exposed SE aspect. 

NWAC forecaster Joe Dellaporta was on Cooper Spur on Thursday. He (and other observers) noted moderate wind transport above 8000 ft, but light winds at 7000 ft near his high point. He found right-side-up snow above the 2/13 crust which increased in depth progressively from less than 8" below 4800 ft to more than 1 ft above 6000 ft. The new snow had widespread weak, faceted surfaces and surface hoar near and below treeline that made for excellent riding conditions, but this interface will be worth tracking moving forward.  He found no concerning test results, suggesting that from the 2/13 interface downward we have a strengthening snowpack. 

About 1.5" of water/16" of snow was recorded at area weather stations through Tuesday morning along with strong to extreme westerly winds.  Mt Hood Meadows pro-patrol triggered 1-2' deep wind slab avalanches on wind-loaded slopes near and above treeline Tuesday morning during avalanche mitigation. At this time, we think that enough settlement and healing has occurred since the last major storm that old, large slabs are becoming unreactive.

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