Good morning. This is Graham Predeger with the Chugach National Forest Avalanche Information Center on Tuesday, February 21st at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
If you are between the ages of 12 and 18 you won’t want to miss Alaska Avalanche School’s Know Before You Go Backcountry 101 course on Friday February 24th and 25th. It is a 1 1/2 day course specifically geared for this age group and targets the basics of avalanche safely. For more details contact the Alaska Avalanche School.
Pockets of CONSIDERABLE avalanche danger exist today above tree line where wind slabs continued to form yesterday. Elsewhere, the danger is MODERATE due to storm snow instabilities. Human triggered avalanches are possible today. Careful snowpack and terrain evaluation will be prudent in order to identify and avoid features of concern as you travel into the backcountry.
Yesterday proved yet anCNFAIC Staff storm day for the forecast area in what has become a moist month. 11″ of water and over 9 feet of snow has been measured at the Center Ridge SNOTEL site (1800′) since February 1st. This is a significant amount of weight on top of our dry January snow. The good news is that we DO NOT have widespread persistent weak layers present in the pack, therefore we HAVE NOT experienced a deep slab instability problem to date. Each recurring storm seems to be bonding relatively well with its neighbors given time. The bad news (depending on your perspective) is that the avalanche danger has been at Considerable or High 18 of the last 21 days, due in large part to storm snow instabilities. This is what we will be dealing with again today in the form of wind slabs up high and loose snow avalanches at and below tree line.
Wind slabs continued to build yesterday at upper elevations until mid-afternoon when the winds abruptly shut down. These slabs may prove reactive under the weight of a skier or snowmachiner and will likely be found most tender on west and southwest facing slopes below ridges, steep convexities and cross-loaded gullies. There is a CONSIDERABLE avalanche danger for these areas today. While ascending into these upper elevations, pay close attention to any signs of instability. It will be important to listen and feel how the snow surface changes over elevation, cluing you in to where these wind slabs exist.
At lower elevations near and just below tree line, sluffing and loose snow avalanches within yesterdays storm snow will be the avalanche issue today. In steep terrain or above a terrain trap, loose snow avalanches can pose a real danger by knocking you off your feet or pushing you into a deadly tree well. In areas where wind did not affected our surface, this most recent storm is showing signs of bonding exceptionally well as a layer due to the warmer air/ surface temperatures during the storm. This is the kind of snow that the Chugach and Kenai Mountains are known for in the fact that it will plaster onto near vertical slopes, defying gravity. Compression tests yesterday mid-storm were showing moderate to difficult shears at the storm interface (CT22). The most recent storm snow is already showing signs of settlement and we can expect this interface to further gain strength today under a relatively mild day of weather.
The rain/ snow line yesterday seemed to be somewhere around 0-100 feet. These lower elevations have also received a considerable amount of water weight over the last several days and weeks. Roof avalanches in the Portage and Girdwood valleys pose a real and warranted concern during this warm, stormy February. Be extra vigilant of what’s above you while walking around town or parking a vehicle.
Snowfall yesterday was intense at times peaking just after noon as the storm rolled through our area and dissipated by sundown. Easterly winds were in the 25-35 mph range (gusts to 60mph) dying down to single digits overnight. We can expect 10-15 mph ridge top winds today from the west (this is a change in direction from the last several days). Temperatures at 4000′ have remained mostly steady over the last several days hovering right around the 20-degree mark.
Today is shaping up to be a relatively quiet day of weather. We can expect some lingering moisture (1-2″) over the forecast area as this weakening system continues north. Temperatures at 1000′ will be in the 27-33 degree under mostly cloudy skies.
Estimated storm totals for yesterday
Turnagain Pass: 10-16″ snow (1″ water equivalent)
Girdwood Valley: 10-16″ (1″ water equivalent)
Summit Lake: 1-2″ (.1″ water equivalent)
CNFAIC Weather Page and the NWS forecast
Kevin will issue the next advisory Wednesday morning. If you get out in the backcountry we want to know what you are seeing. Please send us your observations using the button at the top of this page or give us a call at 754-2369. Thanks and have a great day.