Wallowa Avalanche Center

Conditions Summary for January 1, 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.

HAPPY NEW YEAR from all of us at Wallowa Avalanche Center
 

The Bottom Line Synopsis:

Things appear to be improving just a bit in the snowpack weakness department, at least way down below all this new snow and firm older snow. The persistent weak layer down where you find the sugary loose snow is beginning to show a little more strength from pits in the last week. The normal, to a bit above normal temperatures have helped for sure over the last couple weeks. We are certainly not out of the woods yet. The snow directly above this weakness is firm and well bonded with just a couple isolated places where a buried surface crust or some other thin weak layer is causing a place where a hard slab could fracture and slide. Still, all the upper layers including all this new snow of today sit on top of that dreaded sugary layer which is sometimes a long distance below the surface and in other places not very far down.

Photo 1: Aneroid Basin avalanche several days old noted this week. Only one I could find.

Since last report southerly winds have kept temperatures fairly moderate and seasonable. No precipitation of significance has occurred since December 22 until just yesterday when the snow pumps turned on. The new snow fallen from last night and today likely will have many isolated areas that will not bond to the older snow surface which consists of surface crusts, granular sparkly type snow or feathery crystals; a variety on all aspects. With this new snow the annoyingly supportable crust (where you stride forward and just as you put full weight on the crust it gives way and drops 3 inches) will no longer be noticed. Natural avalanche activity reports have slowed to a crawl until today when they just might creep back into the spotlight.

Photo 2: Another view of Aneroid Basin avalanche several days old noted this week.

Concern 1: New snow instabilities and wind transported snow. The new snow overnight has been lighter in density but has slowly changed to a more dense/moist snow. There will likely be variable bonding of the new snow to the old snow, weaknesses within the new snow (density changes) and much drifting and wind slab development. The winds will continue moderate to strong from the S and W throughout the weekend. Cornices are likely to build off exposed ridges and summits and wind slabs/pillows will develop mostly on N -> E aspects (but be aware of crossloading) from the forecasted wind direction. Ski cuts, hand pits and test slopes with minor consequences may go a long way in helping to understand this new snow stability.

Concern 2: The persistent weak layer lower down in the snowpack. This sugary granular layer will become more loaded with this new snow. With the occasional collapses WAC has experienced as recently as Wednesday (12-30) it is still known that this layer is sensitive to weight and therefore to a trigger (skier, snowmobile, etc.). Again, likely trigger points are thinner snowpack areas such as rock bands/outcrops, rows of bushes or trees, convex slopes, and so forth. This weakness is nearest ground level on the southerly aspects of the N & E Wallowas and in all of the southern Wallowas. It’s in the lower third of the snowpack on the northerly aspects of the northern and eastern Wallowas. If an avalanche releases on this layer it is likely to be big, possibly as deep as ground level.

Concern 3: Coverage. Maybe soon we can cease talking about this. It’s getting better. S -> W aspects exposed to the sun, above treeline and ridges and summits were still quite bare as of 12-29. At or below treeline where the wind can’t get in, the S -> W seems to require just slightly elevated awareness for logs, rocks, etc..

Concern Summary:

The bond of the new snowfall (and within the new snow) to the old snow surface are the primary layers of concern. Secondary layer of concern is  the additional loading from wind transport and human weight (trigger) causing a possible deep slab avalanche running on the weak loose sugary crystals. Evaluate those layers carefully, before entering avalanche terrain.

Very latest reports from Charla as of Thursday 12-31-09, 2 pm. Just got down from Wing Ridge. It was 29F when we left the parking lot and 20F at the huts a little later, SW wind 15-20 G 30 MPH, Snow blowing sideways. We hiked up above the huts onto the Middle Ridge but the snowpack was too thin, blown off. Dug down on ENE aspect at 7600 and only 2 ft of cover, bottom 8”€� sugar loose granular. At the huts (7200 ft)  average total depth 32”. The snow that was precipitating were small wet crystals, getting larger as day progressed and temps dropped. Nice snow on NE aspects but skiing very gingerly due to hazards.

The Juicy, Techie Stuff:

Pits this week look very similar to last weeks. A bit more densification this week. Perhaps this overburden, warmer temps and plain old time are helping to rearrange some crystals and give us the slightly greater strengthening and bonding I’m seeing in the snowpack. I’m seeing a bit more cohesion in the weak layer of facets above the rock hard old snow layer down below.

Figure 1: This NNE aspect profile @8100 feet is quite similar to a W aspect profile at 7800 feet in the same basin, amazingly. NNE 0484559E 5004059N. W 0484392E 5005318N.

The fact that I’m seeing STH’s reasonably consistently is a good sign. BUT, these are in the deeper snowpack areas and where the snowpack is thinner (likely trigger point) the shear strength appears weaker. I’m still noting in diagrams that the most notable and widespread weak layer is within the loose, large, striated facet layer above the concrete snow in the northern/eastern Wallowas. And, see Connelly Brown’s snowprofile of the Southern Wallowas where we see this same weak layer is right down near the ground.

Figure 2 : Norway Basin, Connelly Brown, a WAC advisor, submitted this snow profile from the southern Wallowas

However, beware that there appears to be a very weak (and hopefully short lived) layer of larger near surface facets that have been covered as of Wednesday 12-30-09 by about 7 inches of soft powder in the southern reaches of the Wallowas.

Photo 3: If you see cracks like this, it’s a warning sign to get off the slope fast.

In the Aneroid Basin I came across a SS-N-R3-D2 on ENE Lookout Mtn. SZ=8200 ft below or just above a cliff band which probably released last weekend (photo 1 & 2). Crown and flanks were very difficult to detect. Some very infrequent medium area collapsing was still noticed mid week. One collapse (intentionally triggered) caused hairline cracks on a slope but no release (photo 3).

Snowpack depths as of 12-30-09:

Same as last weeks report. But that’s changing today.

Photo 4: Pit photo of diagram. Saw is inserted at the bottom of the sugary layer @20cm.

Photo 5: Weather and snow cover conditions of the day near Tenderfoot Pass and Pete’s Point (12-29-09).

Photo 6: Quiz: What might be under the bump covered with snow?

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.

Snowfall last night (Thursday) began slightly lighter in density but quickly rose to a medium density and has and will vary in density throughout the forecast period (Sun night). Snow levels will increase to near the 6000 foot level today. Precipitation should diminish by afternoon today  with accompanying mostly cloudy skies and off  and on flurries through Sat. night. Winds will be from the SW generally throughout Friday and Saturday and fairly strong (15 gusting to 30). Sunday continues cloudy with some flurries before another weak wave of moisture moves in overnight Sunday into Monday. Expected accumulations at 8000 feet, about 10 inches total (QPF's = .75 inches) through Sunday. Long range models indicate a series of light precipitation events through Wednesday and seasonable temperatures.

General Announcements:

Winterfest Poker Run: We will be setting up a booth at the Chief Joseph Days Rodeo Grounds, Thunder Room, January 9th at 7am. Stop by the booth and see how avalanche practitioners do their work, what tools they carry and most importantly what safety equipment you should carry and know how to use when traveling in avalanche terrain.

FREE Avalanche Awareness Talk on Tuesday January 12^th. It’s at the Joseph Community Center at 6 pm and part of the fabulous Eagle Cap Extreme activities at Race Central. The Payette Avalanche Center is visiting us here to assist us in the talk. Great videos of real avalanches, photos, etc., then some really good info on how to become Avy Savvy, learn the basics and how to learn more. He’ll even bring some props that show with a special sand-like material why one snow layer slides on another. AND IT’S FREE!!!!

Current Regional Weather Synopsis:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
340 AM PST FRI JAN 1 2010

.SHORT TERM...TODAY THROUGH SATURDAY...A SECONDARY WAVE MOVING ALONG
A FRONTAL BOUNDARY WILL CONTINUE TO PRODUCE AREAS OF MIXED PRECIP
THROUGH THIS MORNING. THIS PRECIPITATION WILL MAINLY BE IN THE FORM
OF SNOW WITH POSSIBLE FREEZING RAIN FROM THE COLUMBIA BASIN
NORTHWARD. ELSEWHERE THERE ARE POCKETS OF COLD AIR REMAINING ALONG
THE BLUE MOUNTAIN FOOTHILLS...HOWEVER THE COLD AIR IS SLOSHING BACK
AND FORTH ALONG THE NORTHWEST SLOPES OF BLUE MOUNTAINS CAUSING A
WIDE VARIETY OF TEMPERATURES RANGING FROM THE UPPER 20S TO NEAR 50.
FOR EXAMPLE PILOT ROCK LAST HOUR WAS 50 DEGREES...AND ABOUT 15-20
MILES NORTH TEMPS WERE IN THE UPPER 20S TO LOWER 30S. THIS BOUNDARY
BETWEEN THE COLDER AND WARMER AIR WILL SIT NEARLY STATIONERY THROUGH
EARLY THIS MORNING AND THEN WILL BEGIN TO SHIFT NORTHWARD SLOWLY BY
THIS AFTERNOON. THIS WILL CAUSE ALL AREAS ALONG THE BLUE MOUNTAINS
AND FOOTHILLS TO BECOME ALL RAIN. SNOW LEVELS WILL RISE TO BETWEEN
5000 TO 6000 FEET BY THIS AFTERNOON CAUSING THE SNOW OVER MOST
MOUNTAIN PASSES TO BECOME RAIN AS WELL WITH JUST POCKETS OF FREEZING
RAIN. WITH ALL THIS BEING SAID FREEZING RAIN ADVISORIES WILL REMAIN
IN PLACE OVER THE LOWER COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS
UNTIL 10 AM...A WINTER STORM WARNING UNTIL 9 AM OVER THE SOUTHERN
WASHINGTON CASCADE EAST SLOPES...AND WINTER WEATHER ADVISORIES OVER
THE CENTRAL WASHINGTON CASCADES...YAKIMA/KITTITAS VALLEYS AN THE
BLUE MOUNTAINS UNTIL 9 AM AS WELL. IN ADDITION THERE WILL BE A WIND
ADVISORY UNTIL 3 PM FOR THE SOUTHERN GRANDE RONDE VALLEY DUE TO
STRONG WINDS THERE AND AN AIR STAGNATION ADVISORY  CONTINUING FOR
THE YAKIMA VALLEY UNTIL AT LEAST 4 PM THIS AFTERNOON.

THERE WILL BE SEVERAL WEAK WEAVES IN THE FLOW WHICH WILL KEEP RATHER
UNSETTLED CONDITIONS WITH ISOLATED TO SCATTERED RAIN AND MOUNTAIN
SNOW SHOWERS OVER THE FORECAST AREA TONIGHT AND SATURDAY...BUT
PRECIPITATION AMOUNTS ARE EXPECTED TO BE VERY LIGHT. 88

.LONG TERM...SATURDAY NIGHT THROUGH THURSDAY. THE EXTENDED MODELS
SEEM TO BE IN FAIR AGREEMENT. AN UPPER LEVEL RIDGE WILL BE OVER THE
AREA SATURDAY NIGHT THROUGH SUNDAY NIGHT. AN UPPER TROUGH MOVES
THROUGH MONDAY AND MONDAY NIGHT. THE GFS HAS A DECENT AMOUNT OF
PRECIPITATION WITH THIS SYSTEM SO HAVE INCREASED POPS SOME FOR THIS
PERIOD. THE UPPER RIDGE RETURNS TUESDAY THROUGH THURSDAY WITH A WARM
FRONT MOVING THROUGH ON FRIDAY. HIGH TEMPERATURES WILL BE MOSTLY IN
THE 30S TO MID 40S.

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