Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday February 17th at 7 am. 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).
-The winds have increased again at all ridgetop weather stations and are currently moderate to strong averaging 21-29mph with extreme gusts up to 66mph.
-The current radar shows a wall of moderate to heavy precip over PWS moving northwest directly towards us.
-In the last 24 hours (4am-4am), the snotel sites recorded 0.5 inches of water at Turnagain Pass,0.6 inches at Grandview, and 0.0 at Summit Creek. Rain fell up to at least 1800′ reducing the total snowpack by 1-2 inches.
-Temps are about the same plus or minus a few degrees at all wx stations this morning compared to yesterday. Temps range from 36 degrees F at sea-level and 25 degrees F at 3800′.
Today’s avalanche danger will remain at HIGH due to new natural avalanches observed yesterday and a heavy weather forecast issued by the National Weather Service.
Yesterday 2/16/2010, we saw new small to medium sized natural avalanches along Seattle Ridge on the Sunnyside to the south of the main parking area that we did not see on Monday 2/15/2010. This means that the natural avalanche cycle has still been active within the last 24-48 hours.
We have already had about an inch of rain-on-snow up to about 2000′ at Turnagain Pass in the past 48 hours, and winds are currently strong on ridgetops at 3800′. What I’m trying to say here is that we currently have red flags at lower elevations due to rain-on-snow and red flags at higher elevations due to new wind.
To add to our list of problems, the National Weather Service sounds pretty confident that we are going to get hit with more precip, warm temps, and wind over the next couple days. The NWS discussion even mentioned,
“RISING FREEZING LEVELS COMBINED WITH LOCALLY HEAVY
SNOWS AT HIGHER ELEVATIONS COULD INCREASE AVALANCHE RISK IN THE
EASTERN KENAI MOUNTAINS”
It looks like this storm will pack a big punch starting tonight.
Many of the recent avalanches we have observed have been happening on steep slopes between 2500′-3000′. If the rain line creeps up to 2500′ as it is forecasted, then we will most likely start seeing large natural avalanches again. Anytime there is a chance for large natural avalanches, there is also a chance for large human-triggered avalanches. As a general rule, it is really bad to be in the mountains when any size of natural avalanches are happening.
Large to very large human-triggered avalanches are a serious concern today because we have 2 dangerous weak layers in our snowpack that have both been avalanching every day since Friday.
The two main weak layers in our snowpack are:
1.A thin breakable melt-freeze crust with surface hoar on top of it. We have seen this weak layer up to 3000′ on multiple aspects on both sides of highway at Turnagain Pass. This weak layer is generally buried 3-5 feet deep. Surface hoar has been observed on top of this layer in several pits, and recently as Sunday 2/15/2010. Not all pits show the surface hoar, and these feathery crystals get smaller as you gain elevation, but you have to give a weak layer like this lots of respect. This combination of surface hoar on top of a crust is historically responsible for the majority of avalanche surprises and fatalities.
2.The Jan 7 rain crust is generally buried 5-7 feet deep. This particular weak layer has been reactive to explosive triggers and most likely has been naturally triggered during our current avalanche cycle. This persistent weak layer has been showing significant signs of instability since its formation last month. This weak layer is widespread on all aspects up to 3000 feet.
WEATHER FORECAST (National Weather Service)
A LONG SOUTHERLY FETCH OF MOISTURE EXTENDING FROM THE NORTHEAST
PACIFIC TO OVER THE NORTH GULF COAST INCLUDING PRINCE WILLIAM SOUND
AND THE EASTERN KENAI PENINSULA DEVELOPS LATE IN THE DAY WEDNESDAY.
SOUTHERLY FLOW WILL BRING WARMER AIR AND LOCALLY HEAVY RAINS TO LOWER
ELEVATIONS ESPECIALLY NEAR CORDOVA AND THE EASTERN KENAI PENINSULA.
THESE CONDITIONS MAY CAUSE SOME MINOR FLOODING OF SMALL STREAMS AND
PONDING DUE TO DRAINAGE ISSUES IN URBAN AREAS BEGINNING LATE
WEDNESDAY NIGHT AND CONTINUING INTO EARLY FRIDAY.
ADDITIONALLY…RISING FREEZING LEVELS COMBINED WITH LOCALLY HEAVY
SNOWS AT HIGHER ELEVATIONS COULD INCREASE AVALANCHE RISK IN THE
EASTERN KENAI MOUNTAINS.
THE WEATHER SERVICE WILL CONTINUE TO MONITOR THE SITUATION AS
RMC FEB 10
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST WED FEB 17 2010
…STRONG WIND THROUGH THURSDAY NIGHT THROUGH PORTAGE VALLEY AND
.TODAY…RAIN…MIXED WITH SNOW AT HIGHER ELEVATIONS. LITTLE TO NO
SNOW ACCUMULATION. HIGHS IN THE MID 30S TO MID 40S. EAST WIND 10 TO
15 MPH EXCEPT EAST 35 TO 50 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN
.TONIGHT…RAIN AND SNOW…HEAVY AT TIMES. SNOW ACCUMULATION UP TO 6
INCHES AT HIGHER ELEVATIONS. LOWS IN THE UPPER 20S TO MID 30S. EAST
WIND 15 TO 25 MPH EXCEPT EAST 30 TO 45 MPH THROUGH PORTAGE VALLEY AND
.THURSDAY…RAIN…HEAVY AT TIMES. HIGHS IN THE MID 30S TO LOWER
40S. EAST WIND 15 TO 25 MPH EXCEPT EAST 35 TO 50 MPH THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM.
Temperature / Precipitation
SEWARD 41 33 39 / 100 100 100
GIRDWOOD 42 34 39 / 100 100 60
Short Term Weather Model Forecasts (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass
Sea-level: temps are forecasted between 34-42 with between 0.5-1.0” of water today
3000′: temps are forecasted in the range of 23-32 degrees F with winds 20-25 mph
6000′: temps are forecasted in the range of 23-32 degrees F with winds 20-30 mph
WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS
3800′-Sunburst Wx Station
Current Temp: 25 (same as yesterday)
Winds: Averaged light to strong 13-28mph with extreme gust of 40mph
RH: 97 (same as yesterday)
2600′-Seattle Ridge Wx Station
Broken. We will fix as soon as possible.
1800′-Center Ridge Wx Station
Current Temp: 32 (1 degree warmer than yesterday)
Precip: 0.5” of water and minus 2” of total snowpack snow due to rain-on-snow
RH: 100 (same as yesterday)
Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Thursday February 18th.