Turnagain Pass

Good morning backcountry travelers this is Jon Gellings with the Chugach National Forest Avalanche Information Center on Wednesday, December 29th 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).

BOTTOM LINE

Today the avalanche hazard is LOW, with pockets of CONSIDERABLE. Natural and Human triggered avalanches are unlikely on most of the terrain throughout our general advisory area, while small to large sized human triggered avalanches are probable in many areas of steep upper elevation windloaded terrain. Be on the lookout for growing pockets of sensitive wind slab in isolated areas at upper elevations.

AVALANCHE DISCUSSION

It looks like we might be getting new snow for the next few days according to weather forecasts, which will potentially give some new stresses to our snowpack. Just to recap a bit of our weather history, we have not received more than 5″ new snow in 24hrs since December 3rd. Now, almost a month later, we have 6-15″ forecasted for our area over the next 24hrs, so this should probably show us how our buried layers of facets and surface hoar will react to some new snow stresses.

The most probable areas to trigger an avalanche today will still be in steep terrain at upper elevations, with present and previous windloading events. It is hard to say exactly where these areas are, because there are likely many differences between one piece of terrain next to Turnagain Arm and a similar piece of terrain down by Johnson Pass. This spatial variability makes it hard to give set-in-stone parameters to our instability, so be careful when evaluating the snow conditions today, and practice conservative decision making if you are heading into steep avalanche prone areas.

One more thing to think about is our buried Thanksgiving Rain Crust. While the snowdepth will be increasing in some areas, keep in mind that the faceting process will likely continue for some amount of time yet. Even though it will be getting buried further down, and thus further from the air-exposed surface layer of snow, there is still a temperature gradient that can drive the faceting process. Hopefully this weak layer will hold its low energy level (Q3), but there is the chance that it will become more energized with the new snow levels. Look for more on this subject in the near future.

Check out an encyclopedia of terms here: www.fsavalanche.org/Encyclopedia.aspx

WEATHER ROUNDUP

Precipitation is falling again in Turnagain Pass, although our storm is not quite here yet. Currently, the radar image shows a few bands of precipitation out in Prince William Sound, which is associated with the small Low pressure system that has been in the Gulf of AK for a while now. Satellite images show that our large predicted storm is currently in the Kodiak area moving our way. As this weather system moves into our area, temperatures are forecasted to rise, giving us the possibility of some rain at some point. This possibility would likely be bad for our snowpack, so we will monitor for these conditions when the change starts happening. As far as wind is concerned, the Seattle Ridge weather station just received its largest wind gust of 24mph since December 8th. While it was a short-lived event and likely only transported a bit of snow to leeward slopes, keep in mind that there are many areas that constantly receive winds that could be of higher speeds. Look for the wind speeds to increase with this new storm as well.

Kevin will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING THE CITIES OF…WHITTIER…SEWARD…GIRDWOOD…

MOOSE PASS

521 AM AKST WED DEC 29 2010

…BLIZZARD WATCH IN EFFECT FROM THIS EVENING THROUGH THURSDAY

AFTERNOON NORTH OF MOOSE PASS…

THE NATIONAL WEATHER SERVICE IN ANCHORAGE HAS ISSUED A BLIZZARD

WATCH…WHICH IS IN EFFECT FROM THIS EVENING THROUGH THURSDAY

AFTERNOON NORTH OF MOOSE PASS.

A STRONG WEATHER FRONT APPROACHING THE NORTH GULF COAST TONIGHT

WILL BRING VERY WINDY CONDITIONS AND MODERATE SNOWFALL TO THE

EASTERN KENAI PENINSULA BEGINNING LATER THIS EVENING. EAST WINDS

30 TO 45 MPH COMBINED WITH FALLING SNOW WILL LOWER VISIBILITIES

AND CREATE POTENTIAL BLIZZARD CONDITIONS. BLIZZARD CONDITIONS WITH

VISIBILITIES BELOW ONE QUARTER MILE ARE POSSIBLE NORTH OF MOOSE

PASS…THROUGH PORTAGE VALLEY…TO ALONG TURNAGAIN ARM. CONDITIONS

SHOULD IMPROVE THURSDAY AFTERNOON AS SNOW BECOMES MIXED WITH RAIN

WITH WARMING TEMPERATURES.

PRECAUTIONARY/PREPAREDNESS ACTIONS…

A BLIZZARD WATCH MEANS THERE IS A POTENTIAL FOR FALLING AND/OR

BLOWING SNOW WITH STRONG WINDS AND EXTREMELY POOR VISIBILITIES.

THIS CAN LEAD TO WHITE-OUT CONDITIONS AND MAKE TRAVEL VERY

DANGEROUS.

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED DEC 29 2010

…BLIZZARD WATCH IN EFFECT FROM THIS EVENING THROUGH THURSDAY

AFTERNOON NORTH OF MOOSE PASS…

…STRONG WIND TONIGHT THROUGH THURSDAY NIGHT THROUGH PORTAGE VALLEY

AND ALONG TURNAGAIN ARM…

.TODAY…SNOW TAPERING OFF TO SCATTERED SNOW SHOWERS LATER THIS

MORNING. SNOW ACCUMULATIONS 2 TO 5 INCHES. AREAS OF BLOWING SNOW.

HIGHS IN THE MID TEENS TO LOWER 30S…COOLEST INLAND. SOUTHEAST WIND

10 TO 20 MPH EXCEPT EAST 15 TO 25 MPH THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM.

.TONIGHT…SNOW WITH AREAS OF BLOWING SNOW. VISIBILITY POSSIBLY ONE

QUARTER MILE OR LESS AT TIMES. SNOW ACCUMULATION 4 TO 10 INCHES. LOWS

IN THE LOWER TEENS TO LOWER 30S…COOLEST INLAND. NORTH TO EAST WINDS

20 TO 35 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 15

TO 30 MPH INCREASING TO 35 TO 45 MPH LATE IN THE EVENING.

.THURSDAY…SNOW BECOMING MIXED WITH RAIN ALONG THE COASTS IN THE

AFTERNOON. AREAS OF BLOWING SNOW. VISIBILITY POSSIBLY ONE QUARTER

MILE OR LESS AT TIMES. SNOW ACCUMULATION 3 TO 8 INCHES. HIGHS IN THE

LOWER 20S TO LOWER 30S. EAST WIND 30 TO 45 MPH EXCEPT EAST 35 TO 45

MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 28 25 32 / 90 100 90

GIRDWOOD 26 21 22 / 80 80 80

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded wind speeds yesterday from 2-9mph, and temps from 16F to 19F. The current temp is 16F with 11mph winds out of the northeast.

-2600′ Seattle Ridge Wx Station-

recorded mostly calm easterly winds yesterday, while temps ranged from 17F to 21F. The current temp is 19F with moderate wind speeds of 16-24mph.

-1800′ Center Ridge Wx Station-

recorded 2-3″ new snow in the past 24hrs, with all of it being from the past 5 hrs. Temps yesterday ranged from 15F to 24F. The current temp is 22F with a total snowpack depth of 55 inches.