Wallowa Avalanche Center

Conditions Summary for March 26, 2010

Disclaimer: Wallowa Avalanche Center assumes no liability for the accuracy of the information contained in this summary. Information provided does not constitute or imply any type of forecast, advisory, or recommendation. Users are warned to use this information at their own risk.

The Bottom Line Synopsis:

On Monday morning (3/22) up to 8” of snow freshened up the surfaces of the mid to upper elevations in most Wallowa Mtn locations. This settled out to about 6” average by Wednesday morning. Early in the week point releases and sluffs seemed to be in the headlines, but that’s old news. Later in the week the headlines read, “Great powder of Monday not bonding to some old surfaces”. Generally the north aspects where old surface crusts/slabs are not found beneath the new snow, the newer snow is bonding to the old snow. All other aspects except the most northerly have some kind of crust issue just below Monday’s storm snow. In many places this interface bond is not that good. Since strong winds this last week were from the south, then north, then south again, wind slab/crust deposits are somewhat widespread. This bonding concern should be prevalent on any upper elevation wind exposed area and any mid to lower elevation area from E -> S -> W that also had seen some sun intervals along with wind.

Photo 1: Looking toward top of S. Bowl from S. Ridge 3-24-10

Latest conditions: Wet avalanche production seemed to be held at bay this week. The surface snow warmed enough to be a pleasant skiing experience by early afternoon but didn’t appear to get mushy enough to get tumbling down the mountain to any degree this week. Northerly aspects in wind sheltered terrain had tremendously good snow. Soft settled powder made for great turning conditions for all lucky enough to enjoy the mid week fun. After the clouds of Sunday and Monday, Tuesday was mostly sunny, Wednesday brought thin hazy clouds and Thursday was overcast. With these conditions we didn’t experience much of a reduction in snow cover excepting perhaps the most southerly facing terrain.

Photo 2: As we know the skin track up the hill can give you many clues on wind slabs that are likely to be worse up high. Here, a one day old skin track is covered with firm wind slab, whereas just to the right of the skin track is soft powder. Photo taken 3-24-10 on S. Ridge of Wing Ridge.

Recent activity: From Wing Ridge area:  Reports with limited detail came in this past week of natural activity north of Whitebark Ridge between the ridge and Redmont Mtn where a crown fracture was spotted. Also a fairly old crown was spotted on the E aspect of the Imnaha Divide from ‘The Burn’ viewpoint. Early in the week some point releases from the new storm snow were occurring on the east facing slopes in the Johnson Creek Basin off of south fork. Also, additional point releases and sluffs were seen on the Fat Ridge aspect sliding down into S. Bowl. Possible snowmobile triggered small avalanche on a steep NE aspect on the ridgeline of Sugarloaf Mtn seen from S. Ridge with a lens.

Photo 3: Ken mentioned the storm of Monday ended with a graupel event. Well here it is on Wednesday 3-24 in a tree well in the Wing Ridge area. The important thing about these styrofoam balls is that they collect in depressions or thickly in basins and can create a weak layer with new snow on top of them. Often they bond well to the layer above/below but not always, especially if thick.

Concern #1: Older surface snow bonding to any crusts/surfaces underneath and new storm snow. The snow of early this week is not bonding well to some crusts or surfaces underneath it. This is somewhat widespread on all aspects at or above treeline but generally only on E -> S -> W aspects below treeline. Some light snow which occurred overnight and into a portion of today (Friday) will hide some of the exposed crusts and additionally load the buried crusts causing more weight on some of the weaker interface layers.

Concern #2: New wind slabs, drifts, pillows and crusts. Wednesday the snow movement began with increasing winds. Yesterday (Thursday) and today the winds are strong and gusty from the south -> west and wind transported snow is a certainty. Look for evidence of transported snow onto the northerly and easterly aspects and be watchful for crossloaded slopes.

Concern #3: Sandwiched crusts and weak layering within the uppermost 18” to 24” of the snowpack. Weakest layers are nearer the surface but there still exists that booby trap buried surface hoar layer somewhere in the range of 12” to about 30” below the surface. And there is that remote chance that the graupel occurrence this week could be found under this most recent snow of today as a weakness in isolated pockets on northerly and easterly aspects at mid to upper elevations.

Concern summary: Watch for bonding of any softer snow to a crust below. Raise antennas for wind effected terrain. A variety of weaknesses exist to 30” below the surface.

Be mindful that spring conditions are right on our doorstep and rapid changes during this time of year are nearly a certainty. We all know that snow hates rapid change whether it be sun, warm air, wind, rain, heavy snowfall rates, etc. etc. Saturday looks to be warm and sunny -> bear these thoughts in mind when traveling about this weekend. Evaluate all the above concerns when traveling around in avalanche terrain.

Average snowpack depths at 8000’:

Northern and Eastern Wallowas:   8” new, 58” total snowpack depth

Southern Wallowas:   no recent data

The Juicy Techie Stuff:

Last weekend (March 20) an analysis was performed below and 12’ to the left of a crown/flank corner of an older (5-7 days old) avalanche at 8100’ on a 37 degree slope. This slide occurred on an ENE aspect of Lookout Mtn in the Aneroid Basin. We believe this avalanche released on the older new/old snow interface from the storm of March 13. It was approx. SS-N-R2-D2. A shovel shear on this weak bed surface was sometimes easy, sometimes moderate. The soft slab depth was approx. 25cm. We received a CT20Q2 and a ECTN20 on this same interface. Higher scores than we would have otherwise expected. The SS had a thin 4F crust on top, followed by 12cm of F, followed by 10cm of 4F+ resting on the bed surface. See ECT video.

Video: ECT test on Lookout mountain

Elsewhere in Aneroid Basin on a W aspect, 7900’, 29 degree slope on March 20 were a triple series of sun crusts with 4F between each. Failure was STHQ3 at 37 cm down from surface. Well bonded with no hints of weakness in the upper meter. No wet snow conditions were noted at this early morning hour.

Having more difficulty distinguishing the buried surface hoar from an otherwise weak facet layer. I suppose it’s becoming metamorphosed where I have been looking.

Photo 4: Pit on east aspect S. Ridge @ 7700 feet. Photo taken 3-24-10. In places the new snow of Monday was not bonding to the crusts and it made skinning up difficult. On N aspects the bonding was better between the old and new snow interface.

Results of other tests performed in the Wing Ridge area on or before March 24.

E aspect, 7700’, 37 degree:  STE down 17cm from surface on a sun crust       of sorts

     CT22Q2 down 75cm (pencil in photo)

N aspect, unknown elev.:   CT11&13Q? 18” down

NW aspect, in the Burn, unknown elev.: CT14Q?  100cm down

Figure 1: General snow profile seen in most regions this week.

Wallowa Mountain Weather Briefing:

We are working directly with the National Weather Service in Pendleton through special briefings to provide you with applicable local mountain weather information. You should always obtain a weather forecast from National Weather Service before undertaking any winter outdoor activities.

Overcast conditions will continue to prevail today (Friday) with the light snow of last night continuing for the morning hours in the mountains. Precip. will then shut down with some clearing possible before nightfall with total storm accumulations of several inches. Winds will be strong today from the west shifting to the NW at 15mph gusting to near 30 on the ridges and summits. Winds will subside on Saturday from the SW at 5-10mph.Temps will rise as the weekend begins. Expect lows around 20 at night with daytime temps on Saturday at or above 40 at 8000’. Some sun will be with us early on Sunday before the clouds roll in once again with another chance of snow in the mountains Sunday afternoon into Monday. Winds will pick up again on Sunday in advance of the next storm.

General Announcements:

April 9 is closing day for the weekly summaries. On that day we will have a host of generalities to watch for between that day and when people have had enough of hiking up with all their gear for 3 turns or some such thing. I grew up as a teen skiing on Tuckermans’ Ravine on Mt. Washington back east where yes they do hike all their gear up for about 3 turns; generally until about July 4.

We are now an official IRS 501(c)(3) non-profit organization. All proceeds you donate to us is fully deductible to the extent allowed by IRS law on your taxes. Please donate so we can begin setting aside important dollar amounts for the multitude of exciting projects we would like to plan for next year. Email us and tell us your thoughts: info@wallowaavalanchecenter.org

Current Regional Weather Synopsis:

.PREV DISCUSSION... /ISSUED 229 PM PDT THU MAR 25 2010/

SHORT TERM...TONIGHT THROUGH SUNDAY...A NEGATIVELY TILTED UPPER
LEVEL TROUGH IS CENTERED JUST OFF OF ASTORIA THIS AFTERNOON AND WILL
AFFECT THE AREA THROUGH TOMORROW. THE MAIN FRONT HAS MOVED OFF INTO
THE ROCKIES AND WE ARE SEEING SHOWERY PRECIPITATION AS A WEAKLY
UNSTABLE ATMOSPHERE IS SETTING OFF SOME SHOWERS. COULD STILL SEE A
FEW ISOLATED THUNDERSTORMS THIS AFTERNOON IN THE EASTERN MOUNTAINS.
THE THUNDERSTORMS SHOULD NOT REACH SEVERE LEVELS BUT COULD HAVE A
FEW LIGHTNING STRIKES...BRIEF GUSTY WINDS AND SMALL HAIL. SHOWERS
WILL CONTINUE THROUGH TOMORROW AFTERNOON AND DECREASE OVER TIME AS
THE TROUGH MOVES EAST. THE SYSTEM WILL CONTINUE TO SEND GUSTY WINDS
OF 15 TO 25 MPH TONIGHT AND TOMORROW OVER MUCH OF THE AREA BUT DO
NOT FORESEE A NEED FOR A WIND ADVISORY AT THIS TIME. AS TEMPERATURES
DROP TONIGHT...SNOW LEVELS WILL DROP TO 2500 TO 3000 FEET...COULD
SEE AN INCH OR TWO OF SNOW IN CENTRAL OREGON AND OVER MOUNTAIN
PASSES WITH UP TO 3 INCHES IN THE HIGHER MOUNTAINS BUT SHOULD NOT
REACH SNOW ADVISORY LEVELS. THE SYSTEM WILL MOVE OFF TO THE EAST
FRIDAY NIGHT AND SHOWERS WILL END AS A RIDGE BUILDS OVER THE AREA.
SATURDAY AND SATURDAY WILL BE FAIR AND WARMER WITH HIGHS IN THE
UPPER 50S TO MID 60S. THE NEXT WEATHER SYSTEM WILL MOVE ACROSS THE
CASCADES AND INTO THE AREA DURING THE DAY ON SUNDAY. SOUTHERLY FLOW
AHEAD OF THE SYSTEM WILL KEEP TEMPERATURES UP SUNDAY BUT MOST OF THE
AREA WILL HAVE A CHANCE OF RAIN IN THE AFTERNOON. GUSTY WINDS WILL
PICKUP AGAIN SUNDAY AFTERNOON WITH THIS NEW SYSTEM. PERRY

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...A WEATHER DISTURBANCE
WILL PUSH EAST OF THE CASCADES FOR A CHANCE OF PRECIPITATION SUNDAY
NIGHT INTO MONDAY. THE TROUGH AND COLD FRONT WILL THEN SWING THROUGH
THE REGION MONDAY AND MONDAY NIGHT FOR CONTINUED PRECIPITATION
CHANCES AND BREEZY CONDITIONS. THE REGION WILL BE IN BETWEEN SYSTEMS
ON TUESDAY WITH A DECREASING THREAT OF PRECIPITATION. MODELS BEGIN
TO DISAGREE WITH THE LOCATION AND STRENGTH OF A LOW PRESSURE SYSTEM
IN THE EASTERN PACIFIC. THE GFS MODEL RUNS TAKE THE LOW FURTHER
SOUTH INTO CALIFORNIA WITH PRECIPITATION ROTATING UP INTO CENTRAL
AND SOUTHERN OREGON. THE EUROPEAN MODEL BROUGHT THE SYSTEM OVER THE
PACIFIC NORTHWEST...HOWEVER MORE RECENT RUNS ARE STARTING TO BRING
THE LOW FURTHER SOUTH...LIKE THE GFS. HAVE KEPT A CHANCE OF
PRECIPITATION IN THE MOUNTAINS AND SLIGHT CHANCE IN THE BASIN
BECAUSE OF THE UNCERTAINTY. IF THE GFS SOLUTION PANS OUT...MOST OF
THE PRECIPITATION WILL BE ACROSS CENTRAL OREGON AND FURTHER SOUTH.
DMH