CNFAIC Avalanche Advisory (Turnagain Pass Area)

Wednesday, May 1st 2013 Turnagain Area Avalanche Advisory

Wendy Wagner — 2013-05-01T10:00:00+01:00

ABOVE TREELING: No rating

BELOW TREELING: No rating

THE BOTTOM LINE

Wow, what a feast or famine winter! We had a fairly late start to the year with an early season dry spell but, the Holiday onslaught delivered the goods - thankfully. And, even though the spring was dry as well, great riding and skiing was at hand during March and April.� More details below in the season roundup.

This is being written on the last day of April, which has been unusually cold and dry. The cold weather has delayed - and maybe even denied - the spring melt down or infamous shed cycle, but we do have warmer and wetter weather moving in for the beginning of May. The snowpack may be old and tired (only 10-18" of snow for April...); however, it is still mostly dry snow and will undergo its transition to a summer snowpack at some point soon. It is this transition that we are concerned about, which is associated with the first week or two when the pack turns isothermal (the same temperature at 32deg F) and loses much of its strength.

BOTTOM LINE: With a lot of cold dry snow remaining in the mountains, the potential for large wet avalanches will continue to be a very real concern through May.� The best way to mitigate this is watching for new avalanches, especially new large avalanches.

PRIMARY CONCERN

SPRINGTIME AVALANCHE TIPS - Timing is everything

Watch for the "shed cycle". One great way (and an old timer rule of thumb) is to keep an eye on the ridgetop weather stations. Avalanche activity often follows multiple consecutive days (usually 3) of above freezing overnight temperatures. This can signal a snowpack with limited refreezing and when followed by warm days (either sunny or rainy) dramatically increases the likelihood of natural and human triggered large wet avalanches. Careful route planning to stay out from under slopes with wet and rotten snow is essential during this period. See below for some additional general springtime tips:

Once the snow has undergone the transition to a summertime pack and is freezing at night and warming during the day (the corn season),hitting the slopes early and getting off them when they become too sloppy is critical..

Mushy snow more than 6" deep is a sign that it's time to exit the area. Following the aspects as the sun heats up the slopes over the course of the day, east to south then west, can make for great riding/skiing days ending in sunny tailgateing.

Keep in mind, cloud cover 'holds in the heat' and can dramatically limit overnight refreezing. A shallow to no refreeze will not only give daytime heating a jump start on weakening the pack, but can produce less than stellar riding conditions.

Beware for warm storms where rain is falling on snow, especially when rain is falling on cold dry snow. This can quickly increase the avalanche danger.

After a new snowfall, watch for the first rays of sun to trigger both slab and loose snow avalanches in the new snow. Often, these initiate just below trees and rocks.

One of the easiest ways to stay safe in the springtime is knowing what kind of surface you are traveling on and under. Hard frozen snow, that easily supports a person and/or snowmachine, is unlikely to avalanche. Soft and saturated snow, deep enough to leave tracks you would not want to ski through when frozen, is a RED FLAG that the snow is losing its strength and becoming ripe to avalanche.
Watch the CORNICES, these are large and likely to keep peeling off for a while.

Last, Don't forget to plan your route back to the car. Does it take you under slopes that were frozen and safe earlier in the day, but now have been cooking in the sun waiting to slide on your return?

MOUNTAIN WEATHER

SEASON WEATHER ROUNDUP
Check out our Weather History�page where you can find our monthly weather charts. Here is the�weather chart for April.

SNOWFALL and SNOW DEPTH -� (Turnagain Pass SNOTEL 1,880ft on Center Ridge)

Seasonal snowfall was 322" (Nov 1 - Apr 30) - in a feast or famine regime. Last season snowfall was 385" for comparison. In fact, of the 322" of snow that fell on Turnagain Pass, 252" (28.4" H2O) fell between Christmas Eve and February 28th. Compared to a meager 70" of snowfall (6.7" H2O) that fell during November, most of December, March and April combined. For the number geeks out there: 78% of our snow fell during only 38% of the season.

Snow depth is shown in the graph below:

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Don't forget about the BeadedStream snow temperature array. This shows snowpack temperature vertically every 10cm (4") and is great for watching the pack turn isothermal.� It's located near the SNOTEL site and will hopefully be up and running until June!

AIR TEMPERATURE -� (Sunburst weather station 3,812ft)

A generally cool season all in all. The early season cold period (Nov-Dec) produced 2-3 feet of faceted snow and subsequently became quite reactive in late December and January once it was buried by the holiday onslaught. There were several large avalanches, including two close calls (Tincan and Repeat Offender). Additionally, the mid-season stormy period was interrupted by a couple days cold snap in late January. The cold snap followed 2 days of rain to 2,500' (late January crust) and is responsible for the weak snow over a crust set up that produced a handful of large avalanches during mid to late February.

WIND -� (Sunburst weather station 3,812ft)
Sunburst had a much milder year for winds, compared to last season when we had record setting gusts. The mid-season stormy period is clearly evident by the increase in easterly wind from Dec 24th till the beginning of March.

Current weather can be found on the�CNFAIC weather page as well as MountainWeather.com's Alaska page.

Thank you for checking the avalanche advisories this season. Have a safe spring and summer!!

�

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Sunday, April 28th 2013 Turnagain Area Avalanche Advisory

Wendy Wagner — 2013-04-28T10:00:00+01:00

ABOVE TREELINE: Moderate
Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Likelihood of Avalanches Natural avalanches unlikely; human- triggered avalanches possible.
Avalanche Size and Distribution Small avalanches in specific areas; or large avalanches in isolated areas.

BELOW TREELINE: Moderate
Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Likelihood of Avalanches Natural avalanches unlikely; human- triggered avalanches possible.
Avalanche Size and Distribution Small avalanches in specific areas; or large avalanches in isolated areas.

THE BOTTOM LINE

Most terrain around the Eastern Turnagain Arm has LOW avalanche danger this morning. Below treeline, the danger will rise to MODERATE late in the day for human triggered wet loose avalanches as temperatures climb. Additionally, there are pockets of MODERATE danger on steep upper elevation slopes where it is possible to trigger a shallow stiff wind slab just below ridgelines.

For Monday, avalanche conditions look to be similar to today. Keep in mind, if warm wet weather moves in mid-week you can expect the avalanche danger to rise.

PRIMARY CONCERN

The north winds have ravaged the upper elevations. We continue to hear of parties feeling collapsing and whoomphing on ridgelines and some able to trigger slabs 2-6" thick. These slabs may be shallow but they are stiff and can be dangerous if triggered in 'no fall' zones (i.e., over cliffs). Since most of the higher terrain has significant wind affect, you are likely to find many areas with a breakable and annoying wind crust along with the scattered areas of wind slab. Unsupported slopes are the most concerning (see the second photo for an example of this). Our unusually cool spring has allowed the facets below these slabs to persist and wintertime cold snow issues to remain above treeline.

Photo is of Graham Predeger monitoring the breakable wind crust Saturday that covers most upper elevation slopes. This is near the top of the Burns glacier ~4,000ft.

SECONDARY CONCERN

Below treeline today, and on southerly aspects with little wind, you can expect the crusty surfaces to warm up late in the day. The cool temperatures and breeze may keep warming limited, however if you do come across a slope with more than 6 inches of mushy wet snow avoid it. If this is the case triggering a wet loose snow avalanche is quite possible and can entrain a lot of heavy snow and run far.

Below is a photo from Saturday. The wet avalanche activity is a few days old (from Tues/Wed) but the picture demonstrates what our mountains look like and the variable nature of the snow conditions.

The much anticipated "shed cycle" has not produced yet and maybe this will be one of those years we don't really see it. The cool northerly flow and clear nights has kept the pack from warming up. However, we do have a warmer system moving in this week so keep your eye out any avalanche activity associated with this.

MOUNTAIN WEATHER

Sunny skies prevailed once again yesterday. Winds were light from the northwest in the 5-10mph range. Temperatures climbed to the mid 20'sF on the ridgelines and low 40'sF at 1,000'.

Today should be another brilliant day in the backcountry with the only change being breezier northerly winds. The winds kicked up last night (averaging 10mph gusting 23mph on Sunburst and bit more at Seattle Ridge) and will be on a slow decrease today. Expect ridgetops to blow in the 10-15mph range with gusts to 30mph from the north. Temperatures will again climb into the 20'sF at the upper elevations and ~40F at 1,000'.

For Tuesday into Wednesday look for a change in the pattern. Models are showing a shift back to a moist southwest flow with the approach of a low pressure system in the north Pacific. Warmer temperatures, clouds and precipitation should return to the Eastern Turnagain Arm.

Helpful weather links:
CNFAIC weather page
MountainWeather.com's Alaska Page�

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This wraps up our final advisory for the season. We will be updating this page around May 1st with springtime avalanche concerns so check back mid-week. Thanks!

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Saturday, April 27th 2013 Turnagain Area Avalanche Advisory

Kevin Wright — 2013-04-27T10:00:00+01:00

THE BOTTOM LINE

Pockets of�MODERATE concern can be found in a couple specific areas today. �The snowpack is generally stable, and most areas are showing a�LOW avalanche danger. �

Recently formed wind slab has been reported to be whoomphing in some places. �That collapse is a serious red flag, meaning that a weak layer exists underneath the stiffer slab. �

Wet avalanches may be a concern if temperatures get high enough this afternoon. �Watch your south exposures as the sun bakes those slopes late in the day. �

PRIMARY CONCERN

Pockets of collapseable and reactive windslab have been reported to us in Turnagain Pass and the Summit areas. We got two reports that areas were whoomphing large sections, to "200 feet away". The observers reported that the weak faceted layer responsible for the collapse was only about 6 inches deep, but it is still cause for concern. Check the observations page to read the full details.

The last couple days had strong wind at the ridge tops with visible plumes between Anchorage and Seward. The snow storm earlier in the week stayed relatively cold and dry at higher elevations, then that snow was transported by the wind. We may still find some of that wind slab this weekend, and it's worth some careful thought if traveling in steep terrain.

The character of this type of avalanche will be relatively small and shallow, more likely at higher elevation, and consist of fairly stiff snow that may support a skier before it fails. The plumes that I saw were oriented north to south, meaning that south facing slopes are more likely to be loaded.

SECONDARY CONCERN

When I was out yesterday it just seemed too cold for wet avalanches to be a concern. That trend may continue this weekend. The wet avalanche concern is still relegated to lower elevation, direct south facing slopes, and late in the day. We got a hard freeze last night, meaning crusts will be thick this morning. It will take a lot of solar energy to break down that crust and penetrate deeper into the snowpack before any real loss of snowpack strength is realized today.

Most of the wet debris piles that you might see today happened just after the last storm from early in the week. This is when we had the most significant warming and soft surface snow was available before it went through multiple melt/freeze cycles.

ADDITIONAL CONCERN(S)

Cornices are still big! At elevations where cornices form, generally well above 2000 feet, we haven't lost much of our snowpack to melting. Remember, cornices lose strength when it gets warm and the snow begins to melt. If the structures are already hanging in an unstable balance, that loss of strength can be the trigger to send them on their way. Or they could be close to falling, just needing another 100+ pounds of stress to tip the balance.

Avoid cornice exposure, especially late in the day when they will be more likely to collapse.

MOUNTAIN WEATHER

We have had no precipitation in over 48 hours. �Wind was mostly calm yesterday, with a northwest wind into the mid teens on Sunburst. �Temperatures got to above freezing at sea level, but the freezing line did not extend all the way to the top of the ridges. �Above 3000 feet stayed fairly cold. �

Last night, temperatures dropped to about 26 degrees at sea level and to the mid teens at 4000 feet. �Highs today will hit the low 40s. �Wind should be light from the northwest. �Mostly cloudy to partly cloudy skies are expected with no precipitation. �

Wendy will issue the next advisory tomorrow, April 28th.

�

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Thursday, April 25th 2013 Turnagain Area Avalanche Advisory

Kevin Wright — 2013-04-25T10:00:00+01:00

THE BOTTOM LINE

The shot of rain and snow has passed, with sunny weather and colder nighttime temperatures back in the mix. �This morning will start with a�LOW�avalanche danger, which will increase to�MODERATE�as the daytime temperatures heat up the surface crusts. �

A lot of small wet avalanches will be visible on the mountains today, which mostly happened during the storm on Tuesday. �Wet avalanche problems are one of larger concerns, but the deeper snowpack still has quite a bit of strength as it remains colder. �

Higher up in the mountains you can find drier snow and some corresponding wind slab issues from new snow.

PRIMARY CONCERN

Wet avalanches will be a concern in the afternoon, mostly on sunny south facing slopes and primarily at lower elevations. Overnight temperatures briefly dipped below freezing at sea level last night, which is colder than two nights ago.

Sometime soon we expect to see a more dramatic warmup of the entire snowpack, at which point stability will become a major concern with larger avalanches a possibility. I don't think we are at that point today, but it can be a tough threshold to predict unless we actually see it happening. Backcountry travel should be more careful late in the day as warmer temperatures cause stability to get worse. If you start seeing spontaneous avalanche activity and you can sink your foot deep into the snow with ease, it's time to be back at the car or another safe location.

SECONDARY CONCERN

You can still find winter at higher elevations. The recent storm dropped at least 5 inches of new snow in some areas, which will be deeper on wind loaded slopes. Be aware that this new snow could be sitting on slick melt/freeze crusts, especially on south facing slopes.

ADDITIONAL CONCERN(S)

I continue to be impressed at the size of looming cornices this late in the season. Colder than normal temperatures have been keeping ridgetop melting to a minimum. Just like wet slab problems, cornices will lose strength as they heat up late in the day. They will become increasingly unstable and may collapse spontaneously with warm enough temperatures. Watch your exposure, especially late in the day when temperatures are highest.

MOUNTAIN WEATHER

Center ridge gained at least half an inch of water equivalent at Turnagain Pass over the last couple days. �At higher elevations this means 5 or more inches of new snow. �

Temperatures last night dropped to 31 degrees at sea level, colder at higher elevations. �We can expect a thin surface crust on the snow this morning.

Today's weather is expected to be sunny and warm. �High temperatures will reach the mid 40s at sea level. �A north wind is expected, which may channel into strong wind at Whittier and Seward. �

We will issue the next advisory on Saturday, April 27th.

�

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Tuesday, April 23rd 2013 Turnagain Area Avalanche Advisory

Wendy Wagner — 2013-04-23T10:00:00+01:00

THE BOTTOM LINE

There is a MODERATE avalanche danger today (Tuesday) below and above treeline. Below treeline, wet loose snow avalanches will be possible with the warm temperatures and light rain. These are likely to be easy to trigger and in the top foot of the pack. Above treeline, watch for shallow wind slabs to develop with 4-6" of snow and moderate to strong easterly wind in the forecast.

Looking forward:

The main issue for Wednesday and into the remainder of the week+ will be the impending "melt down" or "shed cycle". This is when the mountain snowpack literally falls off the slopes and very large and destructive avalanches can occur. This period usually lasts around 2 weeks and is on our doorstep. Once the cycle begins, travel in valley bottoms, and most places for that matter, are at risk as debris can be large, run quite far and bulldoze through just about anything. Stay tuned for Kevin's forecast on Thursday to see where are sitting with this.

PRIMARY CONCERN

Yep, we are finally getting our warm April temperatures and a little rain and snow today. We only have a small amount of precipitation forecast but, the main concern is how the snowpack is reacting to the warm temperatures and cloud cover. Below treeline, watch for the top 6-12+" of snow to lose cohesion and be easily pushed down any slope over 35 degrees. Mainly wet loose avalanches will be possible to trigger but there is also a potential for wet slabs around a foot deep to pull out. It is best to steer clear of any slope with soft wet snow deeper than 6". Additionally, buried crusts in many areas can provide great bed surfaces allowing any slide triggered to run further than expected.

As for the larger and more dangerous slides: Once the entire pack warms up to a balmy 32F (0C) we call it isothermal and it looses much of its stability. This is the primary contributor to the shed cycle. Right now the snowpack at 2,000' is not quite warm enough (see image below). However, snow can change rapidly and with that the avalanche danger. You can keep tabs on the evolution of the snowpack HERE but also keep in mind this is only one point (2,000' on Center Ridge) and the snowpack varies considerably with elevation and aspect.

SECONDARY CONCERN

Above treeline we can expect several inches of heavy snow today with moderate to strong east winds. The new snow is likely to stick rather well to the existing surface at the mid elevations but upper elevations should see dryer snow with more of a classic winter wind slab problem. Expect any fresh slab found at these upper elevations to be sensitive as they will be sitting on either crusts (wind or sun) or loose faceted snow.

ADDITIONAL CONCERN(S)

Cornices are likely to start peeling off any day now with our recent warm temperatures. They have the potential to trigger avalanches below, entrain large amounts of snow and run into valley bottoms. Again, with the springtime warm-up on the way, be very wary of traveling in drainage bottoms for the next several weeks.

MOUNTAIN WEATHER

Yesterday we had a brief return to the sunny skies that have characterized�April to date. Temperatures were quite warm, around 30F on ridgetops and the upper 40's at 1,000ft. Ridgetop winds during the past 24 hours averaged ~15mph with gusts to 35mph from the east. The last snowfall ended 13 days ago, April 9th. Overnight, cloud cover has moved in and temperatures have only dropped 5-10F - it's feeling like spring finally.

Today a warm, wet and windy, but fast moving, system is moving through from the Gulf. We should see around 4-6" of dense snow above treeline and .3" of rain below treeline throughout the day (rain/snow line ~1,500ft). Temperatures look to rise back to 30F on ridgetops and the mid 40's at 1,000ft. Winds will remain from the east in the 15-20mph range with gusts to ~40mph.

Wednesday we should see partly cloudy skies as the system moves out and we return to a dry, but warm, period for the remainder of the week.

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Kevin will issue the next advisory Thursday morning, April 25th.

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