Sun, April 21, 2013 Turnagain Pass Avalanche Forecast

Sun, April 21st, 2013

Alpine

Above 2,500'

1 - Low

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


Travel Advice	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.	Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.	Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.	Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches	Natural and human-triggered avalanches unlikely.	Natural avalanches unlikely; human-triggered avalanches possible.	Natural avalanches possible; human-triggered avalanches likely.	Natural avalanches likely; human-triggered avalanches very likely.	Natural and human-triggered avalanches certain.
Avalanche Size and Distribution	Small avalanches in isolated areas or extreme terrain.	Small avalanches in specific areas; or large avalanches in isolated areas.	Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.	Large avalanches in many areas; or very large avalanches in specific areas.	Very large avalanches in many areas.

Avalanche Problem 1

Wind Slabs

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

More info at Avalanche.org

We do not have great conditions for wind slab development with little snow available for transport (much of the surface is in the form of crusts) and only up to an inch of new snow in the forecast. However, there are two things to keep in mind which will keep wind slab on the radar. First, winds have been predominantly out of the northwest for the past week but shifted around to an easterly direction yesterday and picked up overnight. And second, many northerly aspects still harbor loose faceted snow that could be blown into fresh drifts. So the question is, will the wind be strong enough and in the right direction to form slabs? It’s possible. For today, watch for signs of visible wind loading and cracking in the snow under you from a drift that may have formed earlier. Any fresh slabs should be shallow (~6″ at best) yet quite sensitive as they’ll likely be sitting on a slick surface.

Avalanche Problem 2

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

Fast running sluffs on steep northerly aspects have been the only avalanche activity we have seen or heard of for the past several days. This will be the case again today so sluff management continues in areas with loose faceted snow. Many slopes however sport varying degrees of sun crust and wind crust along with many many tracks.

With cloudy skies and cool temperatures in store today the threat of wet loose snow avalanches will be low.

Weather

Sun, April 21st, 2013

Yesterday marked the 11th day in a row with sunny skies, cold nights and no precipitation. We may break that streak today – but if we do it’s likely only in the cloud cover category. We have a weak low pressure system in the Gulf that is pushing clouds and a little bit of moisture in from the east. Overnight, temperatures have dipped to the mid 20’sF at most locations and the upper teens on the ridgelines with winds increasing from the east with averages ~13mph and gusts to 28mph.

Today, we may see a trace to an inch of snow down to 500′ and a rain/snow mix below. Daytime temperatures should rise into the 30’s at 1,000′ and mid 20’s on the ridgetops. The easterly winds look to remain in the 15-20mph range with occasional stronger gusts.

Tonight and into Monday we may see 1-2 inches of snow accumulation above 1,000′ and a rain/snow mix below. Temperatures look to be warm on Monday afternoon to the upper 30’s at ridgetops and 40’s at 1,000′ with mostly cloudy skies.

Below is a little recap of our season’s precipitation (Turnagain Pass SNOTEL data). We were catching up to average water numbers by February but have dropped off into the 75-80% of normal during our dry April to date.

I will issue the next advisory Tuesday morning, April 23rd.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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