Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday, March 25, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur. This advisory expires in 24 hours and does not apply to operating ski resorts or highways/railroads.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Winds are increasing this morning gusting as high as 68mph at Mile 43 Peak. Temps are increasing at sea-level, but decreasing at ridgetops. NOAA is forecasting up to 2 inches of water along the coast in Prince William Sound. NOAA also has a blizzard warning in effect this morning (see NOAA forecast below).
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 24 degrees (2 degrees colder than yesterday). 0.3 inches of water and 2 inches of new snow. Total snowpack depth is 91 inches.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Is recording a temp of 17 degrees (4 degrees colder than yesterday). Winds have been strong since 8pm last night averaging 34-45 mph with gusts 67 mph.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Show a storm getting stronger (982-973mb) as its moving toward the Gulf of Alaska
As of 5am this morning….Show a green monster of heavy precip moving NW into Prince William Sound, and the satellite shows the center of this storm is still under the Aluetians but moving or direction. So this jives with the surface maps.
Primary avalanche concerns
-Buried Sun Crust. All southern aspects. This crust is buried under about 2 feet of snow. Before it was buried on Sunday 3/22/09, it had surface hoar on top of it and was super fragile with facets growing underneath it.
-Buried Surface Hoar. These feathery crystals were observed on all aspects from the parking lots to the ridgetops before getting buried by 1-2 feet on Sunday 3/22/09. Avalanches were observed on this layer on NW aspects below 2500′.
-Below 3000 feet. The “Janurary Hurricane” rain crust buried under 3-5 feet of surface snow. There is a layer of weak sugary faceted snow on top and below this hard rain crust. Stability tests as of 3/24/09 are still showing Q2 failures in the facets above this rain crust. This weak layer is still showing signs of life, and probably will become very dangerous if it gets any sort of rapid load, especially rain and rapid warming from intense sun.
-Sea-level up to at least 3800 feet (Probably higher). The thin “glazed donut” freezing rain crust that formed 3/5/09 has been observed throughout the Turnagain Arm area. This layer formed almost everywhere on all aspects from the parking lots to the ridgetops. This layer is now buried under about 3 feet of snow. This layer is not showing much action in snowpits anymore, but its still there.
AVALANCHES AND SNOWPACK
This morning will start off with moderate “elevated caution”, but the avalanche hazard could increase rapidly if this storm hits us as hard as NOAA is predicting.
NOAA is predicting this storm to pack a big punch with up to 2 inches of water along the Prince William Sound coast and 20-35 inches of snow forecasted inland. If the crystal ball is correct, then I’ll probably be throwing up the skull and crossbones tomorrow.
The buried sun crust was reactive to ski cuts on Monday 3/23/09 where slope angles increased above 35 degrees. Not much happened until we reached these steeper slope angles, and then it was easy to trigger 2 foot deep slabs that broke up into large blocks all around you after you were out in the middle of the slab. I would not want to be on a big slope with that kind of situation. It was the heavy type of slab that grabs your skis and pulls you down.
Yesterday, that sun crust was more difficult to trigger with compression test scores in the 20’s, but it was reactive to the weight of a skier as he stepped onto an AK block.
Yesterday, we saw a couple of avalanches below 2500 feet on NW aspects on Tincan and Sunburst. These were most likely natural avalanches that occured on Sunday during the height of the storm. None of these slabs had tracks leading into them but they were close to some of the normal skin tracks; so, either they occured naturally or they were triggered remotely. We did a crown profile on one of these avalanches at 1800 feet on Tincan and confirmed the failure layer was buried surface hoar. You could see it very easily in the side wall of the pit. These avalanches were not very big, but they show that there is an intact layer of buried surface hoar that was unstable enough to have been triggered remotely or naturally. Compression tests on this layer showed hard failures in the 20’s on 3/24/09. I’m not sure how this layer will react to a major load of new snow.
The buried sun crust and buried surface hoar will be the most likely problem layers if we get hit with this storm. It has been super windy up at Turnagain Pass since last night so there is already a chance for triggering larger avalanches than what happened on Sunday 3/22/09 or Monday 3/23/09. The chance for bigger wider avalanches will increase if this storm hits us with more precip.
Here’s my latest thoughts on the January Hurricane layer…
We know that it is confined to lower elevations. Thats why we are concerned about the steep slopes in places like Placer/Skookum, Seattle Creek, and Kern/Peterson, because those slopes start at sea-level instead of 1000 feet like they do along the highway at Turnagain Pass. Its important to look at some topo maps, and pay attention to where elevations range from sea-level to about 2800 feet. Eventually something is going to tip the balance with this weak layer. Maybe this storm will do it. CNFAIC Staff factors are now that it is getting warm and sunny, I’m starting to get nervous about direct southern aspects on steep slopes at lower elevations. So we need to be aware of temps staying above freezing for prolonged amounts of time. The CNFAIC Staff big possibilty for triggering this deep instability will be rain on snow; so, watch out when that happens.
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF…WHITTIER…SEWARD…GIRDWOOD…
459 AM AKDT WED MAR 25 2009
…BLIZZARD WARNING IN EFFECT UNTIL 9 AM AKDT THIS MORNING FOR
PORTAGE VALLEY AND TURNAGAIN ARM…
THE NATIONAL WEATHER SERVICE IN ANCHORAGE HAS ISSUED A BLIZZARD
WARNING…WHICH IS IN EFFECT UNTIL 9 AM AKDT THIS MORNING.
A WEATHER FRONT MOVING THROUGH THE AREA IS PRODUCING EAST WINDS TO
70 TO 80 MPH THIS MORNING THROUGH PORTAGE VALLEY AND EASTERN
TURNAGAIN ARM. COMBINED WITH MODERATE TO HEAVY SNOW VISIBILITIES
WILL BE REDUCED TO A QUARTER MILE OR LESS AT TIMES THIS MORNING IN
BLOWING SNOW. CONDITIONS ARE EXPECTED TO IMPROVED LATE THIS
MORNING AFTER THE FRONT PASSES AS WINDS DIMINISH AND TEMPERATURES
RISE TO ABOVE FREEZING.
A BLIZZARD WARNING MEANS SEVERE WINTER WEATHER CONDITIONS ARE
EXPECTED OR OCCURRING. FALLING AND BLOWING SNOW WITH STRONG WINDS
AND POOR VISIBILITIES ARE LIKELY. THIS WILL LEAD TO WHITE-OUT
CONDITIONS…MAKING TRAVEL EXTREMELY DANGEROUS. ALL TRAVEL AND
OUTDOOR ACTIVITY IS STRONGLY DISCOURAGED.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT WED MAR 25 2009
…BLIZZARD WARNING IN EFFECT UNTIL 9 AM AKDT THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…
.TODAY…SNOW IN THE MORNING…THEN SNOW MIXING WITH RAIN ALONG THE
COAST IN THE AFTERNOON. AREAS OF BLOWING SNOW REDUCING VISIBILITY TO
A QUARTER MILE OR LESS IN THE MORNING THROUGH PORTAGE VALLEY AND
TURNAGAIN ARM. PRECIPITATION MAY BE HEAVY AT TIMES IN THE AFTERNOON.
SNOW ACCUMULATION 3 TO 6 INCHES ALONG THE COAST AND 6 TO 12 INCHES
INLAND. HIGHS IN THE MID 30S TO MID 40S. EAST WIND 15 TO 25 MPH
EXCEPT EAST 35 TO 45 MPH WITH GUSTS TO 80 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM IN THE MORNING.
.TONIGHT…SNOW MIXING WITH RAIN ALONG THE COAST IN THE
EVENING…THEN SNOW AFTER MIDNIGHT. PRECIPITATION MAY BE HEAVY AT
TIMES IN THE EVENING. SNOW ACCUMULATION 5 TO 10 INCHES ALONG THE
COAST AND 12 TO 18 INCHES INLAND. LOWS IN THE MID 20S TO MID 30S.
EAST WIND 20 TO 40 MPH DECREASING TO 10 TO 15 MPH AFTER MIDNIGHT.
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 35 TO 50 MPH
WITH GUSTS TO 60 MPH IN THE EVENING.
.THURSDAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE
AFTERNOON. SNOW ACCUMULATION 2 TO 5 INCHES. HIGHS IN THE MID 30S
TEMPERATURE / PRECIPITATION
SEWARD 45 35 46 / 100 100 100
GIRDWOOD 41 28 42 / 100 100 100
This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Thursday, March 26. Thanks and have a great day.