Monday, December 2, 2013

Backcountry Avalanche Forecast

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CGS: Colorado Geological Survey
  Backcountry Avalanche Forecast for Southern San Juan
Issued: 12/02/2013 6:37 AM by Josh Hirshberg
Highlights
Persistent Slabs are the primary avalanche problem in the Southern San Juan zone. Watch for a buried layer of surface hoar in the Wolf Creek Pass area. The most likely place to trigger Persistent Slabs will be on slopes over 35 degrees that face northwest, north, and northeast. Evaluate snow and choose terrain carefully.
Avalanche Danger
The avalanche danger for the Southern San Juans is MODERATE (Level 2) on all aspects and elevations.
5 Day Danger Rose Trend:  Southern San Juan
Missing Rose
Nov 27, 2013
Missing Rose
Nov 28, 2013
Missing Rose
Nov 29, 2013
Missing Rose
Nov 30, 2013
Missing Rose
Dec 1, 2013
Current Danger Rose
Southern San Juan
Missing Rose
Dec 2, 2013
Snow & Avalanche Discussion
Persistent Slabs, as the name implies, have stuck around in the Southern San Juan zone. Near Wolf Creek Pass, a layer of surface hoar is buried about 3 feet under thick slabs.  Surface hoar can result in wide propagation and surprising avalanches. These Persistent Slabs are now difficult to trigger but can still result in a large and dangerous avalanche on northwest, north, and northeast aspects. Closer to Coal Bank Pass these same northwest through northeast slopes harbor a layer of facets 2-3 feet below the snow surface. Persistent Slabs in this part of the zone may be more sensitive. Throughout the zone, the coldest northerly slopes will have well-developed faceted weak layers near the ground. Digging and using snowpack tests, like compression test and extended column tests are great ways to evaluate Persistent Slabs.

Observers have reported impressively large surface hoar growth in the southern San Juan Mountains. This persistent weak layer is not a problem today, but it could become an issue if buried. Keep an eye on the surface hoar to see if it gets buried by fresh slabs in the coming storm. Today may be the last chance to check out backcountry conditions before the next winter storm. We'll be watching closely as the storm materializes Tuesday into Wednesday. If forecasted snow amounts are correct, we may see a jump in avalanche danger later in the week.
Media
Images and Snowpits
Weather Discussion for 11,000ftIssued: 12/02/2013 5:16 AM by Spencer Logan
A major winter storm begins tonight. The Grand Junction Forecast Discussion has the details. Today is not really the calm before, because ridge top winds will be strong and gusty. Ridge top and down slope winds will be very strong over and east of the Front Range, Sawatch, and Sangre de Cristo ranges. Temperatures will be relatively mild, and skies mostly to partly cloudy. The action begins after midnight as an arctic cold front moves south from Wyoming. With good jet support, cold air advection, and abundant Pacific moisture, snowfall will be heavy to intense along the cold front. The front reaches the I-70 corridor Tuesday morning and stalls for a while, which adds uncertainity to the forecast and will change the snowfall amounts and locations quite a bit on Tuesday. It begins the southward march Tuesday afternoon, bringing the intense snowfall to the Central Mountains late Tuesday and into Wednesday morning. This period should have the heaviest snowfall statewide. By Wednesday, upper level flow turns southwesterly as the trough deepens. That shifts the focus of the most intense snowfall to the San Juan Mountains. The trough deepens and begins to shift east Wednesday night. Snowfall will decrease, but continues through Thursday. A COLD arctic airmass moves in as the trough shifts east, and weekend temperatures will be bitter.
Weather Forecast
FieldsMondayMonday NightTuesday
Temperature (°F)30 to 3515 to 2025 to 30
Wind Speed (mph)10 to 2010 to 2015 to 25
Wind DirectionSWWSWSW
Sky CoverPartly CloudyMostly CloudyMostly Cloudy
Snow (in)003 to 6

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Link to this forecast:  https://avalanche.state.co.us/pub_bc_avo.php?zone_id=8&arc_sel_bc_avo=10496&display=printerfriendly

 
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