Bollettino valanghe

Rattlesnake

West Central Montana Avalanche Center
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Pericolo valanghe

Wed
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Last night, the forecast area received 2 to 4 inches of light snow, with the southern Bitterroot favored. Expect another inch or two with light northwesterly winds and moderate gusts today. Triggering small isolated slides in freshly wind drifted snow is possible below exposed ridgelines in the Seeley Lake and Rattlesnake zones. Steer clear of pillow-shaped hollow-sounding snow on slopes steeper than 35º. Avoid them by sticking to protected or wind-scoured areas.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–1.5

    Winds will be light northwesterly with moderate gusts. Wind slab will build throughout the day and will be mostly isolated to upper elevations on or below exposed ridgelines. Wind slabs will form over various melt-freeze crusts, which may provide a good surface for them to slide on. 

    Look for stiff hollow-sounding snow, wind lips, and cornices that indicate the presence of a nearby wind slab.

    Avoid them by sticking to protected or wind-scoured areas. If in doubt, stick to slopes less than 35º, and dial it back further if snowfall rates or wind speeds intensify.

    (2/2/2022) Example of wind slab and shooting cracks from the Rattlesnake.  Photo: Jeff Carty

Avalanche Discussion

A low-pressure system in the Desert Southwest is causing northwest flow bringing light snowfall to the forecast area. A more direct low-pressure system hit is expected later tonight and into Wednesday, putting the February spring foray behind us. The fresh snow is falling over various melt-freeze crusts on all aspects below approximately 7,000 feet. Above that, various crusts and windboards exist. These surface crusts and windboard have the snowpack locked in place, and there is little to no snow available for transport before the 2 to 4 inches we received last night. 

Last week saw shrinking snow depths as warming continued to melt and consolidate the snowpack. Observations reported a large cornice fall near Lapi Point in the Central Bitterroot that likely occurred between February 9th and the 11th. Loose wet avalanches closed Hwy 93 south of Lost Trail, and Cornice fall in the southern Missions triggered loose wet slides that entrained snow on Thursday, February 10th. We've had no reports of unstable snow in the past few days. 

Buried surface hoar in the Lolo area and facets near January freeze/thaw crusts remain 6 to 18 inches deep. However, these layers appear to have healed some over the past week of warm temperatures and sold nightly refreezes. They were not propagating in extended column tests in pits we dug yesterday in the Elk Meadows area. Reactive persistent layers could still exist elsewhere in the forecast area. Developing surface hoar grains (2-4 cm tall) were found on the surface of isolated protected pockets on a north aspect near Skookum Lake yesterday. 

Light snow is in the forecast. Last night, two inches fell in the Rattlesnake, Seeley Lake, and northern Bitterroot. The southern Bitterroot received up to 4 inches. Another 0 to 2 inches is forecast today and up to 5 inches for tonight. These are not huge totals, but it does demand some respect as the new snow will fall over an icy and consolidated snowpack that hasn't seen fresh snow for over a week. Temperatures have dropped since the storm arrived, and the new snow may take time to bond to the old surfaces. Expect light northwesterly winds with moderate gusts. 

Many thanks to the folks who have been submitting observations. They are beneficial for assessing conditions throughout the forecast area. Please continue to submit them here:

https://missoulaavalanche.org/submit-an-observation/

Ski and ride safe.

Regioni coperte