Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Friday, December 3rd 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). This advisory will expire 24 hours from the posting date/time.
The National Weather Service has issued a BLIZZARD WARNING for today. If the weather hits us the way they are forecasting, then it will increase the avalanche danger this afternoon and evening. This storm looks like it is going to pack a big punch.
-TEMPS: Are warming at lower elevations by 7-10 degrees compared to yesterday.
-PRECIP: 0.0 inches of water fell within the past 24 hours. The National Weather Service is forecasting significant precip today that will increase the avalanche danger if it hits us.
-WIND: Ridgetop winds have been mostly light in the last 24 hours, but are increasing at all ridgetop weather stations this morning with strong gusts up to 36mph. These increasing winds support the forecast by the National Weather Service for a BLIZZARD WARNING today.
TEMPS, PRECIP and WIND are the 3 main weather factors that affect avalanche conditions. 2 out of these 3 are forecasted to increase today; which, will also increase the avalanche danger.
Today’s avalanche danger rating is based on complete speculation due to the high confidence level of the National Weather Service with today’s weather forecast. Right now, as of 6am this morning, the avalanche danger is MODERATE. We are already, however, seeing strong gusts on ridges. If we get new precip in addition to these winds, the avalanche danger will increase rapidly to CONSIDERABLE. If this blizzard hits us, dangerous avalanche conditions will exist. Statistics show that the majority of avalanche deaths occur when the avalanche danger is rated CONSIDERABLE.
The 3 main ingredients for an avalanche are:
1. a slab
2. a weak layer
3. a bed surface.
Our current snowpack conditions include a BED SURFACE (check!) consisting of a 1/4 inch thick rain crust that extends up to the ridgetops that is widespread throughout the Turnagain Arm area. This crust has all the characteristic to become a very dangerous bed surface because it has a couple of inches of light, dry, cold snow sitting on top of it. This layer of cold snow will act as a WEAK LAYER (check!) if a dense wind slab forms on top of it.
The only ingredient we are currently missing is a significant wind slab. If the weather forecast becomes reality, then NATURAL AVALANCHES will become possible, and HUMAN-TRIGGERED AVALANCHES will become likely.
MEDIUM to LARGE AVALANCHES on specific terrain like steep wind loaded slopes near ridges will be the primary concern today. Secondary concerns will include small avalanhces on steep rollovers in many areas. Glide Crack Avalanches are also still a secondary concern.
The glide cracks and glide avalanches continue to be present, with new ones being observed region-wide on a daily basis. Be aware of your travel routes and try to avoid spending time below the cracks. The only way to reduce your risk from glide avalanches is to avoid traveling below the obvious cracks.
This photo (taken 11/16/2010) shows a good example of a glide avalanche and a glide crack on the southern aspect of Cornbiscuit. For scale take note that the crack is 4-6 feet deep. The glide crack on the left hand side of this photo has already avalanched; while, the glide crack on the right is still a hazard that could avalanche any day. Avoid traveling underneath glide cracks just like the one on the right hand side of this photo.
The Nation Weather Service weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF…WHITTIER…SEWARD…GIRDWOOD…
1044 PM AKST THU DEC 2 2010
…BLIZZARD WARNING IN EFFECT FROM NOON TO 9 PM AKST FRIDAY…
THE NATIONAL WEATHER SERVICE IN ANCHORAGE HAS ISSUED A BLIZZARD
WARNING…WHICH IS IN EFFECT FROM NOON TO 9 PM AKST FRIDAY. THE
BLIZZARD WATCH IS NO LONGER IN EFFECT.
A WEATHER FRONT WILL BRING STRONG WIND AND HEAVY SNOW TO WESTERN
PRINCE WILLIAM SOUND BEGINNING AT MIDDAY FRIDAY AND ENDING DURING
THE EVENING. SOUTHEAST WIND WILL INCREASE TO 40 TO 55 MPH ACROSS
THE REGION WITH 50 TO 65 MPH WIND EXPECTED IN PORTAGE VALLEY AND
TURNAGAIN ARM. SNOWFALL OF 4 TO 8 INCHES WILL COMBINE WITH THE
WIND TO PRODUCE BLOWING SNOW. VISIBILITIES WILL BE REDUCED BELOW
ONE QUARTER MILE AT TIMES UNTIL WINDS DIMINISH IN THE EVENING.
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 AKST FRI DEC 3 2010
…BLIZZARD WARNING NOW IN EFFECT FROM 9 AM THIS MORNING TO
9 PM AKST THIS EVENING…
.TODAY…SNOW AND BLOWING SNOW DEVELOPING THIS MORNING AND BECOMING
HEAVY AT TIMES IN THE AFTERNOON. VISIBILITY ONE QUARTER MILE OR
LESS AT TIMES. SNOW ACCUMULATION 4 TO 10 INCHES. HIGHS IN THE
MID 20S TO LOWER 30S. SOUTH TO EAST WIND INCREASING TO 25 TO 45 MPH
WITH GUSTS TO 60 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.TONIGHT…SNOW AND BLOWING SNOW TAPERING OFF OVERNIGHT. VISIBILITY
ONE QUARTER MILE OR LESS AT TIMES IN THE EVENING. ADDITIONAL SNOW
ACCUMULATION 3 TO 7 INCHES. LOWS IN THE LOWER 20S TO LOWER 30S…
COLDEST INLAND. SOUTH TO EAST WIND 25 TO 40 MPH WITH GUSTS TO
55 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…DECREASING TO
10 TO 20 MPH BY MIDNIGHT.
.SATURDAY…A CHANCE OF SNOW SHOWERS IN THE MORNING…THEN SNOW
SHOWERS LIKELY IN THE AFTERNOON. SNOW ACCUMULATION UP TO 2 INCHES.
HIGHS IN THE LOWER 20S TO MID 30S. SOUTHEAST WIND 15 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 33 29 33 / 100 100 70
GIRDWOOD 29 25 32 / 100 100 70
WEATHER STATION SUMMARY for Turnagain Pass:
3800′-Sunburst Wx Station
Temp: (5am): 15 (2 degrees colder than yesterday morning)
Winds: In last 24 hours have been light to moderate averaging 1-28mph with strong gusts up to 26mph
2400′-Seattle Ridge Wx Station
Temp: (5am): 18 (1 degree warmer than yesterday morning).
Winds: In last 24 hours have been light to strong averaging 1-29mph with a strong max gust of 36mph.
1800′-Center Ridge Wx Station
Temp: (6am): 24 (8 degrees warmer than yesterday)
Precip: 0.0″ in last 24 hours 44″ total snowpack depth (minus 1″ due to settlement)
The next advisory will be issued tomorrow Saturday morning 12/4/2010 at 7am. If you get out in the backcountry send us your observations using the button at the top of this page or call and leave a message at 907-754-2369. Thanks and have a great day.